20 February 2018, Volume 31 Issue 2
    

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    China Journal of Highway and Transport. 2018, 31(2): 1-1.
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    China Journal of Highway and Transport. 2018, 31(2): 1-1.
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  • Key Issues and Research Progress of Shear Strength Theory of Unsaturated Soil
    FU Hong-yuan, MA Ji-qian, SHI Zhen-ning, ZENG Ling
    China Journal of Highway and Transport. 2018, 31(2): 1-14.
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    The shear strength of unsaturated soil was closely related to the mineral composition, mesoscopic structure and water content. Many scholars have proposed varieties of formation mechanism, calculation methods and testing methods of the shear strength of unsaturated soil. In order to summarize the existing research results and deepen the cognition of the shear strength theory of unsaturated soil, some key problems in the development of the shear strength theory of unsaturated soil were reviewed. First of all, the microstructure differences of different unsaturated soils were discussed and the micro mechanism of the shear strength of unsaturated soil was analyzed. The differences of changing laws of the unsaturated shear strength between sandy soil and silty soil were compared and analyzed. Then, several typical strength formulas of unsaturated soil shear strength were summarized, and the different unsaturated parameter selection methods were analyzed. Finally, many new instruments and methods for testing the shear strength of unsaturated soil were introduced, such as the unsaturated direct shear test, unsaturated triaxial test and unsaturated ring shear test. Some foreign research results were still in a blank state in China, which was worth using for reference for domestic scholar. The future research direction of shear strength theory of unsaturated soil is prospected according to the above analysis. First and foremost, the effect of soil particle interaction and soil water interaction on the macro shear strength of unsaturated soil should be further investigated from the microscopic perspective. Second, the calculation parameters of the unsaturated shear strength should be determined according to the comprehensive factors of soil type, water content state and stress state. The corresponding calculation method should be put forward, and unsaturated soil strength theory tends to be applied in the practical engineering. Last but not least, the existing shear strength testing methods of unsaturated soil should be further modified to control a variety of test variables. The test method should be optimized, and the efficiency and accuracy should be further improved.
  • Research Status of Instability Mechanism of Rainfall-induced Landslide and Stability Evaluation Methods
    WEN Hai-jia, ZHANG Yan-yan, FU Hong-mei, XIE Peng, HU Jing
    China Journal of Highway and Transport. 2018, 31(2): 15-29,96.
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    In order to deepen the understanding of rainfall-induced landslides, the research status of the instability mechanism and stability evaluation methods of rainfall-induced landslides was discussed. On this basis, the outlook of future research focuses was provided. The main types, characteristics and controlling factors of rainfall-induced landslides were first summarized, and then the instability mechanism of landslides of soil slide, namely, deep landslide controlled by matric suction and shallow landslide dominated by seepage force were mainly discussed. With regard to the stability analysis, introductions were conducted on infiltration concepts and infiltration models, whilst some improved infiltration models based on Green-Ampt model were presented. The stability analysis methods of rainfall-induced rock landslides were briefly presented, and emphasis was given to the stability analysis of landslides on the basis of unsaturated soil mechanics as well as limit equilibrium method. Some common stability analysis methods were chosen and put into the practice, and safety factors were compared to improve the mutual understanding of the essence. Finally, shortcomings of current researches on instability mechanism and stability evaluation methods were investigated from the perspective of research method, research object and application of research results. Meanwhile, effectiveness and suitability of related research methods, the importance of the research object and the prospective application of research results were discussed. On this basis, further researches should emphasize on the field investigation and application of monitoring technology, the combination of research methods, the interdisciplinary comprehensive analyses, the consideration of the uncertainty involved in rainfall infiltration and stability analysis, and high-tech application.
  • Improvement, Testing and Application on Goodman-Bray Method for Stability Analysis of Toppling Slope
    CHEN Zu-yu, CAI Yun-peng, WANG Yu-jie, SUN Ping, FENG Shang-xin, BAI Xing-ping
    China Journal of Highway and Transport. 2018, 31(2): 30-38.
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    In order to confirm the feasibility and applicability of the improved Goodman-Bray method for slope toppling analysis, the in-depth analyses, test and design of the improved method was conducted. The effects of different column width, ground water level and prestress reinforcement of anchors on the slope stability was discussed respectively, based on a number of engineering cases including slopes in the first district of Liushugou, intake high slopes of the release structure at the left bank of Longtan Hydropower Station, slopes in the south of Tianshengqiao No.2 Hydropower Station.The analyses were conducted on the stability of the topping slope of the release structure at Lianghekou Hydropower Station under construction. The results show that, firstly, the safety factor decreases with the decrease of the column width. Secondly, when water level of inside and outside slope tends to stabilize, the filling of reservoir water has no substantial influence on the stability of the slope. The safety factor of the topping slope dramatically decreases with the rapid drawdown of the outside slope. The application of anchors greatly contributes to the increase of factor of safety. The feasibility of the improved Goodman-Bray method can be further improved in the process of the future design.
  • Slope Stability Analysis Based on Morgenstern-Price Method and Improved Radial Movement Optimization Algorithm
    JIN Liang-xing, FENG Qi-xuan, PAN Zhuo-fu
    China Journal of Highway and Transport. 2018, 31(2): 39-47.
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    In order to accurately determine the critical non-circular slip surface location of slope and its corresponding safety factor, a new heuristic optimization algorithm, namely, radial movement optimization algorithm was used to analyze the stability of slope. By adjusting the data structure of the original algorithm and enhancing the self-feedback ability of particles, an improved radial movement algorithm (IRMO) was proposed. The safety factor was solved by dint of the strict Morgenstern-Price method. Newton-Raphson method was deployed to obtain the iterative calculation formula of the safety factor F and the parameter of the inter-slice force λ for Morgenstern-Price Method under the force balance and moment balance. Based on the Morgenstern-Price method, IRMO was used to analyze the slope stability. Through two typical slope examples and a complex example of seawall slope, IRMO was compared with the unmodified radial movement algorithm from the aspects of stability, accuracy and computational efficiency. At the same time, IRMO was compared with other algorithms such as particle swarm optimization, improved particle swarm optimization and so on. The results show that compared with the unmodified radial movement algorithm, results of critical slip surface based on IRMO by continuously searching for 20 times overlap in some degree. It proves that IRMO is more stable. The safety factor of IRMO converges faster with generation, which proves that the computational efficiency of IRMO is higher. Compared with particle swarm optimization and improved particle swarm optimization, the critical slip surface of IRMO is consistent with that of other algorithms. The result of safety factor is closer to the referee's answer, and the standard deviation reaches the smallest. The feasibility and superiority of IRMO in slope stability analysis are proved. Through the example of a complex seawall slope, the reasonable result of safety factor and the critical slip surface position of the slope are obtained by IRMO. It shows that this algorithm can correctly evaluate the slope stability, and can be applied in the actual project.
  • Research on Analysis Method for Stability of Perched Transient Saturated Slope（in English）
    JIANG Zhong-ming, LI Xiao-fan, WU Zhong-cai
    China Journal of Highway and Transport. 2018, 31(2): 48-56.
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    In order to analyze the stability of the transient saturated slope caused by rainfall infiltration, the un-stability mechanism of transient saturated slope under the condition of rainfall infiltration was analyzed by considering the influence of unit weight, matric suction and transient water pressure. The distribution law of transient water pressure in the transient saturated area was discovered, and the corresponding computing methods for transient water pressure were proposed. A modification on Janbu limited equilibrium method with the consideration of transient water pressure, matric suction and great changes was made by dint of the distribution condition whether the slope was situated at the perched transient saturated area. And a routine which could search the both circular and non-circular type slice surface was programmed for the analysis of transient saturated slope's stability. The variation law of stability factor and sliding mechanism of perched transient saturation slope was investigated. The results show that the stability is mainly influenced by matric suction in the beginning of rainfall period, as the depth of transient saturated area is shallow. With the increase of the depth of the transient saturated area, transient water pressure in the slope becomes the main factor controlling the slope stability, and the safety factor of the slope gradually decreases. The safety factor of non-circular type is smaller than that of circular type with the increase of the depth of the transient saturated area. Besides, the potential sliding surface of non-circular sliding mode becomes shallower with the decrease of the depth of the transient saturated area. It is also indicated that under the same condition, the depth of non-circular sliding surface is always smaller than that of circular sliding surface with the increase of the depth of the transient saturated area. The depth of the most dangerous mansard sliding surface decreases with the increase of the transient saturated area. The depth of the circular sliding surface decreases first and then increases. This variation trend is related with the transient water pressure on the bottom of the slice and the shear strength parameters. A shallow non-circular slice mode is easier generated in the perched transient saturated slope.
  • Three-dimensional Stability Analysis of Complex Gentle Incline Rock Slope
    WANG Lin-feng, TANG Hong-mei, TANG Fen, YE Si-qiao, WU Chuan-sheng, XIA Yu-chao
    China Journal of Highway and Transport. 2018, 31(2): 57-66.
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    In order to establish the three-dimensional stability analysis method of complex gentle incline rock slope,the gentle incline rock slope which includes stratum and multi-group structural plane was taken as the research object. Firstly, according to the survey data of field, the contact relationship of adjacent rock blocks of gentle incline rock slope was divided into detachment, surface contact and line contact. According to the contact method of each rock, the corresponding contact mechanics mode was constructed, and the load-bearing condition of the rock was also defined. Based on the material mechanics, the calculation method of interlayer load in three kinds of contact cases was established by regarding vertical displacement and the corner of rock as intermediate variables. Then, according to the load of each rock, the tensile stress, shear stress and torque at the rear structural plane of rock were calculated. The first, second and third type of stress intensity factors of the structural plane were obtained based on the fracture mechanics method, and further, the calculated expressions of the combined stress intensity factors of the structural plane were obtained. Finally, the ratio of the fracture toughness of the structural plane to the joint stress intensity factors was used as the stability coefficient of each rock. By comparing the relationship of size between the stability factor of the rock and 1, whether the blocks are stable could be judged. The method of this paper was applied to gentle incline rock slope of Yangcha River in Qijiang。The results show that the location of the top-slope failure calculated by the calculation method in this paper is basically consistent with the location where the on-site slope has been cracked, which means that the three dimension stability analysis method of complex gentle incline rock slope is reasonable. Therefore, the method constructed in this paper can provide primary theoretical support for the prevention and control of the gentle incline rock slope.
  • Analysis of Rainfall Infiltration Process and Stability of Soil Slope with Multilayer Structure（in English）
    HU Qing-guo, YUAN Ning, LIU Deng-sheng, HE Zhong-ming
    China Journal of Highway and Transport. 2018, 31(2): 67-74.
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    In order to analyze the infiltration process and stability variation of soil slope with multilayer structure under different rainfall conditions, a method for calculating the rainfall infiltration depth and stability of multilayer soil slope were proposed based on rainfall infiltration mechanism and theoretical calculation formula of rainfall infiltration depth of homogeneous soil. The proposed method and numerical analysis method were used to calculate the depth and stability of rainfall infiltration and stability of soil slope with multilayer structure. The results show that the formula for calculating the infiltration depth of multilayer slope under the influence of rainfall intensity and rainfall time duration is established. The results obtained from the formula are basically consistent agree with the numerical analysis results. That is to say, the formula can better reflect the rainfall infiltration process of the multilayer soil slope. In the process of rainfall infiltration, the volumetric water content and pore water pressure near the slope surface dramatically increase and change greatly at the interface of soil layer. Meanwhile, the slope surface reaches saturation firstly, and the volume water content of second layer soil reaches saturation subsequently. The safety factor of slope decreases with the increase of rainfall infiltration depth in the process of the rainfall infiltration. The safety factor changes suddenly when the wetting front reaches the soil interface. On account of the difference of permeability coefficients between different soil layers, it is easy to form seepage flow parallel to the slope surface at the interface of the soil layer, thus causing a wide range of fluctuation of the slope safety factor. The slope is prone to be failure this moment.
  • Analytical Study on Block-flexure Toppling Failure of Rock Slopes Subjected to Seismic Loads
    ZHANG Hai-na, CHEN Cong-xin, ZHENG Yun, ZHOU Yi-chao, DENG Yang-yang
    China Journal of Highway and Transport. 2018, 31(2): 75-85.
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    Due to the brittleness of rock and irregular joint, block-flexure was one of the most common type of toppling instability. Based on the limit equilibrium, a geomechanical model of block-flexure toppling failure subjected to seismic loads was established by the method of step-by-step analysis. The analytic formula of block-flexure toppling failure was deduced, and the effect on the stability and failure mode of toppling rock slope subjected to seismic loads was analyzed. Using the geomechanical parameters of the slope, the number of the potential failure to rock and seismic influence coefficient was considered as variables in the stability analysis, and calculation procedure of the safety factor and failure mode of slope under different variables was coded by adopting MATLAB. In addition, the analytical solution of this paper was compared with the method of transfer coefficient and numerical simulate. The results show that the stability of slope decreases gradually with the increase of seismic inertial force, and sliding failure and toppling failure crosswise appear due to the different potential failure modes of some adjacent rock.However, the whole failure mode gradually changes from toppling failure to slipping failure with the increase of k.The toppling failure mode is prone to occur with the increase of cutting slope angle and the decrease of the stability of slope. The influence of rock thickness on the slope is different under different seismic influence coefficients.
  • Three-dimensional Seismic Stability Limit Analysis of Two-stage Slope by Kinematical Approach
    ZHANG Biao, WANG Xuan, ZHANG Jia-sheng, ZHANG Jia-hua, HUANG Fu
    China Journal of Highway and Transport. 2018, 31(2): 86-96.
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    In order to provide a reference for the seismic design of the two-stage slope, the stability of two-stage slopes under the earthquake was investigated. Based on the three-dimensional failure model, the seismic force was introduced into the calculation models by the quasi-static method. On the basis of the upper bound theorem of limit analysis, the energy dissipation of the failure state of two-stage slopes was analyzed, whilst analytical solutions of the stability factor were deduced by the fictitious power principle. By virtue of the exhaust algorithm, the optimal upper bound solutions under constraint conditions were obtained. The validity of the proposed method was demonstrated by comparing the results with ones of existing researches. Parametric analysis was carried out to investigate the impact of diverse parameters on the stability of two-stage slopes, including depth-width ratio, the internal friction angle, the depth coefficient, slope angles and the seismic force. The results show the depth-width ratio affects the stability factor greatly. With the increase of the depth-width ratio, the three-dimensional effect of two-stage slopes gradually decreases, and the problem becomes a plain-strain problem in the end. The minimum depth-width ratio of the transformation from three-dimensional problem to a plain-strain problem is given at different computational accuracy. The internal friction angle, depth coefficient and slope angles have significant influences on the stability factor. In order to improve the stability of two-stage slopes, the slope angles should decrease and the height of upper-stage slope should increase. The horizontal and vertical seismic forces affect the stability of two-stage slopes evidently. Failing to take them into consideration will cause a difference as high as 40% and 15% respectively.
  • Stability Analysis of Seismic Slope Considering Tenso-shear Coupling
    YIN Chao, LI Wei-hua, LI Jian, CAI Guo-qing, ZHAO Cheng-gang, CHI Ming-jie
    China Journal of Highway and Transport. 2018, 31(2): 97-105.
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    The Mohr-Coulomb strength criterion was modified based on the tenso-shear coupling. Three classical seismic waves were input on the bottom of slopes with different slope heights and different slope aspect ratios, whilst the dynamic stability analysis of the slope was carried out. First, an explicit iterative sub-increment method was used to formulate the subroutine of Mohr-Coulomb strength criterion in consideration of the tenso-shear coupling. Then in order to simulate the seismic action of the slope, the equivalent seismic load was input on the bottom of model, and the viscoelastic artificial boundaries were also added on the truncated boundary. To verify the correctness of subroutine, a unit subjected to compression and tension was taken as an example. Compared with the existing seismic slope analysis, the results would be dangerous if the tenso-shear coupling was not taken into consideration. Three seismic waves were vertically input on the bottom of slope. The difference of safety factors of slopes with different slope heights and different aspect-ratios were analyzed on the basis of two strength criteria. The results show that:slopes with different shapes (slope heights and slope aspect ratios) which under different seismic waves (El-Centro, Kobe and Northridge) have different safety factors. However, the slope safety factor decreases with the increase of slope heights and slope angles. Safety factors considering tenso-shear coupling are lower than that without considering tenso-shear coupling. And the variation of safety factors has its own characteristics. The slope response of seismic wave band is influenced by the change of heights and aspect ratios. Therefore, the tenso-shear coupling of geomaterials as well as changing laws of different slope heights and different slope aspect ratios should be considered when analyzing the stability of seismic slope.
  • Research on Susceptibility Mapping of Earthquake-induced Landslides Along Highway in Mountainous Region
    XIE Peng, WEN Hai-jia, HU Dong-ping
    China Journal of Highway and Transport. 2018, 31(2): 106-114.
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    Earthquake-triggered landslides was a key factor influencing highway capacity in mountainous area. An accurate susceptibility mapping along highway was necessary for the adoption of proper preventive measures and normal operation of highway. In this paper, on the basis of geographic system (GIS) technology, logistic regression (LR) model was established to investigate susceptibility in an area of 8km around highway in Wenchuan Country and Lushan Country. In the process of research, firstly, based on triggering mechanism of earthquake-induced landslides, the research achievements and results of site investigation, thirteen main factors that influence earthquake-induced landslides were identified, including elevation, slope gradient, slope position, slope aspect, curvity, micro-landform, lithology, distance from streams, distance from faults, normalized differential vegetation index (NDVI), peak ground acceleration (PGA), distance from highways, and mean annual rainfall. Then, based on the geospatial database of Wenchuan Country, 10 sets of samples were trained by R software, and the LR model was developed. Finally, a map of the earthquake-induced landslides susceptibility classes for Wenchuan Country was obtained by dint of the ARCGIS platform. The susceptibility values of earthquake-induced landslides were divided into five categories, from very low to very high. The application in Lushan Country tested the validity and stability of the LR model, a map of the earthquake-induced landslides susceptibility classes for Lushan Country was obtained. The AUC values of the ROC curve for the model were 0.921 and 0.783 respectively, corresponding to Wenchuan Country and Lushan Country. The results show that the susceptibility map generated by the LR model is identical with the true distribution of earthquake-induced landslides, and the LR model is with high stability. Therefore, the LR model can be applied to predict the earthquake-induced landslides along highways in other mountainous regions with similar geological environment conditions.
  • Method for Analysis of Micropile Ultimate Resistance in Soil Slope Stabilization
    SUN Shu-wei, ZHANG Kui, ZHU Ben-zhen
    China Journal of Highway and Transport. 2018, 31(2): 115-123.
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    To provide a reference for the design and safety evaluation of stability of micropile-reinforced soil slopes, test on the bearing characteristics of a micropile under the lateral sliding body deformation was carried out, in allusion to the loess, glacial till, and weathered shale widely adopted in the practical engineering. Using the numerical simulation method, considering the pile-soil interaction and nonlinear characteristics of soil, a model for analyzing the ultimate resistance of the micropile for soil slope reinforcement was established. Taking the ultimate bending moment of micropile cross section and maximum horizontal displacement of micropile head as controlling conditions, the analytical method for determining the ultimate resistance of the micropile was proposed. The analysis results and test results were compared. The deformation mechanism, failure mode and the ultimate resistance of the micropile for reinforcing the loess, glacial till, and weathered shale were analyzed. The results show that the constructed model can well predict the ultimate resistance of the micropile for soil slope reinforcement. The ultimate resistance of the micropile with diameter 115 mm under the lateral deformation of sliding body with thickness of 60 cm is about 10-20 kN. The ultimate resistance of a micropile varies with the types of slope materials, and it will provide the greater ultimate resistance for a higher-strength slope. The failure mode of the micropile for soil slope reinforcement is bending failure due to the exceeding moment capacity of section cross, and the damage appears at the place 4 times the micropile diameter below the sliding surface. The horizontal displacement of micropile head increases linearly with the lateral sliding body deformation at the beginning. And then, with the increase of the lateral sliding body deformation,there exists a clear gap between the micropile head and ground.
  • Upper Bound Analysis of Stability of Three-dimensional Reinforced Slopes Based on Nonlinear Failure Criterion（in English）
    HOU Chao-qun, DENG Xin, SUN Zhi-bin, DIAS D, XU Jing-shu
    China Journal of Highway and Transport. 2018, 31(2): 124-132.
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    In order to investigate the stability of three-dimensional reinforced slopes under two kinds of reinforcement models, namely, uniform reinforcement and triangular reinforcement on the basis of nonlinear Mohr-Coulomb failure criterion, three-dimensional failure mechanism was constructed by dint of upper bound theory in limit analysis. And the internal energy dissipation equations of reinforcement in different reinforced modes were derived. Then the stability problem of three-dimensional reinforced slopes could be transferred into an explicit optimization process, and the formulas of stability coefficient were obtained. The results were calculated by MATLAB software and compared with the previous achievement for validation. Further calculation and discussion were conducted to investigate the effects of nonlinear parameters m, the ratio of slope width to height (B/H), different reinforcement modes and strength (k0) on three-dimensional stability. The results show that the stability coefficient Ns decreases with the increase of m, and with small slope angle (no more than 60°), m has a great impact on Ns. The nonlinear characteristics of the slope are relatively significant. The stability coefficient Ns decreases with the B/H and decreases rapidly when B/H<5, especially when B/H<2. Besides, the coefficient Ns becomes stable when B/H approaching 10. Furthermore, the triangular reinforcement is better than uniform reinforcement. The stability coefficient Ns increases linearly with the reinforced strength k0, but the changing rate is not significant. Some project proposals will be provided for the practical use. The three-dimensional analyses are required for reinforced slopes when B/H is small, in order to be consistent with the actual engineering. To avoid unsafe design, the nonlinear characteristic of criterion should be considered when the slope angle is small. The priority goes to the triangular reinforcement if the engineering condition allows.
  • Analysis on Coupling Model of Permafrost Slope Reinforced by Frame Structure with Anchors（in English）
    DONG Jian-hua, DAI Tao, DONG Xu-guang, SUN Guo-dong
    China Journal of Highway and Transport. 2018, 31(2): 133-143.
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    In order to clarify the working mechanism of frame supporting structure with anchors in the cold region, a coupled mathematical calculation model of heat-moisture-stress was established. The coupled model was analyzed by the finite element method, and a calculation program was written based on the MATLAB software.Besides, the program was verified by the existing experimental research. Through the examples, the distribution laws of the temperature field, moisture field and stress field of the slope and the freeze-thaw reaction of the supporting structure were obtained.The results show that the upper part of slope is greatly influenced by temperature, and the active layer is nearly saturated when it melts.And there exists the supersaturated "bubble" at the bottom of slope. In addition, the shear stress in the process of the freezing whose maximum value is twice as large as that in the process of thawing is evenly distributed. The slope is stable during this process. While there appears a shear stress mutation at the interface between active layer and stable frozen soil layer during the thawing. The slope is unstable, and the interface is the potential slip surface.In a freeze-thaw cycle, the axial force of anchor bolt, the internal force of column and the horizontal displacement increase first and then decrease, and all of them increase with the increase of the slope height. The laws of structural internal force and horizontal displacement under the three conditions from the largest to the smallest are freezing stage, thawing stage and the initial stage.The axial force at the anchor head in each soil layer dramatically increases during the frost heaving process, while the increase amplitude gradually decreases in the axial direction. In the process of thawing, the anchor force and the internal force of column decrease significantly, with a residual deformation produced.Therefore, when the permafrost slope is supported by frame anchor, the supporting structure is supposed to be designed and calculated under the frost heaving condition.
  • Research on Sliding Failure Mechanism of Gently Inclined Bedding Compound Rock Mass Slope Under Hydraulic Drive
    YANG Kuo-yu, CHEN Cong-xin, XIA Kai-zong, SONG Xu-gen, ZHANG Hai-na, LU Zu-de
    China Journal of Highway and Transport. 2018, 31(2): 144-153.
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    In order to conduct a quantitative research on the stability of gently inclined compound rockmass slope under the hydraulic drive, taking a similar slope in Pengjiawan of Shanghai-Chengdu Expressway as an example, a targeted calculation model of simplified mechanics was established on the basis of the upper bound method of limit analysis. In this calculation model, firstly, a strain velocity field allowed in institution was constructed according to the displacement coordination conditions and the plastic mechanics associated with the law of flow. Secondly, according to the principles of fluid mechanics, the hydraulic pressure distribution model suitable to the gently inclined bedding compound rockmass slope was established on the basis of E. Hoek and J. W. Bray's assumptions. Through the analysis of the features of hydraulic pressure distribution inside the slope, the hydraulics including the uplift pressure of potential sliding surfaces, the dynamic pressure of potential sliding surfaces and the fissured hydraulic pressure at the back edge, were directly related to the water filling height of the fissure at the back edge. On this basis, the criterion of sliding instability of slope expressed by the critical water filling height and the critical rainfall intensity was developed respectively. According to the criterion, it was clear that the slide failure of slope might occur along the potential sliding surface with the smallest stability coefficient when the water level at the back edge reaches the critical value or the rainfall intensity reached the critical value. Based on the mechanical model, the value of critical water filling height of the fissure at the back edge and the critical rainfall intensity at the slope landslide in the project case were calculated, and the specific position of sliding surface in sliding instability of slope was discussed. Meanwhile, the sensitive factors of slope stability were also carried out. The results show that the thickness of the bottom rock mass only affects its own stability, and when the dip angle of rock mass is less than 15°, the stability of each potential sliding surface is greatly affected by the dip angle. Under the hydraulic drive, the decline of slope stability is mainly caused by uplift pressure of the potential sliding surfaces and fissured hydraulic pressure, and the hydrodynamic pressure has almost no effect.
  • Active Earth Pressure Calculation of Rigid Retaining Walls with Limited Granular Backfill Space
    LIU Zhong-yu
    China Journal of Highway and Transport. 2018, 31(2): 154-164.
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    The classical Rankine or Coulomb earth pressure theories were established on the basis of the infinite soil behind the retaining walls, so they are inappropriate in estimating the active earth pressure on retaining walls with limited backfill space built in mountainous regions or retaining structures for foundation pit built close to the existing basement. Taking a rigid retaining wall with the granular backfill built adjacent to a stable rock face as a research object, it was assumed that the outward horizontal translation of the wall made the backfill in the limit equilibrium state, the slip surface with the linear type or the mansard appeared through the wall heel. And the soil arch in the backfill took the form of a circle under the plane strain condition. Considering the mean shear stress between level soil layers in the failure wedge, the differential level layer method was introduced to obtain a new formulation for estimating the active earth pressure. In order to verify the accuracy and rationality of the proposed formulation, the predictions from the equation were compared with the centrifuge model test results in the literature. On this basis, taking these retaining walls with triangular-section or rectangular-section backfill as examples, the influences of the inclination angle of wall back, the slope angle, the interface friction angle between the wall and the backfill, the interface friction angle between the rock face and the backfill, the internal friction angle of backfill and the width of backfill on the active earth pressure distribution were investigated. The results show that:for the wall with limited backfill space, the distribution of active earth pressure along the depth is generally nonlinear, and the location of its resultant is possibly higher or lower than one third of the wall height. For the wall with wide backfill, the value of the resultant of active earth pressure is possibly greater than the solution based on the Coulomb theory. In addition, the inclination angle of the slip surface is less than that based on the Coulomb theory for the wall with rectangular-section backfill space.
  • Stability Assessment Method for Subgrade with Underlying Rectangular Cavity
    ZHAO Heng, XIAO Yao, ZHAO Ming-hua, YANG Chao-wei
    China Journal of Highway and Transport. 2018, 31(2): 165-170,180.
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    In order to present a stability assessment method for subgrade with underlying cavity, a simplified mechanical analysis model was established based on the bearing capacity of subgrade in Karst areas, and equivalent calculation model was further obtained. By dint of the complex variable function, the mapping function identification of arbitrary cross sections of the rectangular cavity was proposed. Meanwhile, the specific expressions of mapping functions for common rectangular sections were also presented. The geostatic stress field influenced by a combination factors between the gravity and subgrade loads was obtained in semi-finite space. On this basis, the major and minor principal stresses were obtained, and the stability of the cavity was evaluated based on Griffith failure criterion. In addition, the theoretical result was validated by case records and the numerical method. The results show that the errors between the predictions and the numerical results are less than 5% for the horizontal stress as well as the shear stress, and 8% for the vertical stress.Besides, the proposed results are in good agreement with the observations in engineering practices, and the proposed method has a reference for the preliminary design. It is worth noting that the lager horizontal and vertical stresses appear at the four corners. The stress variation ranges are significant due to stress concentrations. In particular, the four corners are easy to be failed in the actual engineering, and the checking computations should be paid special attention.
  • Lateral Swelling Pressure of Expansive Soil and Its Effect on Gravity Retaining Wall（in English）
    ZHANG Rui, LIU Zheng-nan, ZHENG Jian-long, ZHANG Bo-ya
    China Journal of Highway and Transport. 2018, 31(2): 171-180.
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    In order to investigate lateral swelling pressure (LSP) of expansive soil under the various vertical load and its effect on gravity retaining wall stability, the test apparatus and method for measuring LSP were designed based on the conventional oedometer. The variation law of LSP of expansive soil from Guangxi Baise with different vertical loads was obtained. A numerical simulation for the development of water content was carried out on an expansive soil embankment, under a long-term effect of specific wet and hot climate condition. Combined with the results of laboratory LSP tests, variations of LSP along the back of wall at rest with the depth and time were analyzed.According to the relationship between LSP and lateral swelling ratio obtained by laboratory tests, the variation of LSP with lateral swelling of expansive soil on back of wall was analyzed. Besides, the impact on the stability against sliding and overturning of retaining wall was also discussed.The results show that the expansive soil can still produce amount of LSP after soaking under the lateral confining and zero upper load condition. The LSP increases significantly with the increase of vertical load ranging from 0 to 50 kPa, and is greater than the corresponding the vertical load.When the value of vertical load is greater than 100 kPa, LSP increases very small and remains stable. When the vertical load increases to the vertical swelling pressure of the specimen in the constant volume condition, the LSP reaches to the maximum.Under the long-term effect of hot and wet climate, soil water content and lateral swelling force along the back of retaining wall gradually increases, and the action point of the force moves down gradually. After 5 years, the variation of water content becomes stable, and the distribution of LSP along the back of retaining wall is the parabola.The lateral swelling force can increase to 3 times of earth pressure at rest, and its action point locates in the middle of the wall.The retaining wall will horizontally move in 2.0 cm under the effect of LSP. The LSP can be extremely reduced, and the stability coefficient against sliding and overturning of the wall will meet the requirement of specifications if a lateral swelling of 2.6 cm of expansive soil is allowable behind the wall.
  • Relation of Wall Displacement-earth Pressure from Active to Passive State
    XIE Tao, LUO Qiang, ZHANG Liang, LIAN Ji-feng, JIANG Liang-wei
    China Journal of Highway and Transport. 2018, 31(2): 181-190.
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    The amplitude of earth pressure either from the initial to active state or to passive state was closely linked with the amount of wall displacement and earth pressure. Based on Mohr circle of stress, the expression between earth pressure from active to passive state and mobilized angle of shearing resistance was derived. According to the established geometric equation of soil shear strain and wall displacement, and the corresponding nonlinear elastic-perfect plastic model between soil shear strain and shear stress under the equal ultimate strain, the equation of the wall displacement and lateral earth pressure was established considering the influence of soil stress-strain behaviors and initial stress state of the backfill. Besides, the equation was also revised to reflect the influence of interface friction between the wall and backfill based on Coulomb earth pressure model. The results show that the major factors affecting wall displacement-earth pressure relation are the initial stress state of the backfill, the slip region, and the soil stress-strain behavior. The required wall displacement increases for reaching active state, and decreases for reaching passive state, with the increase of the initial lateral earth pressure coefficient, making the wall displacement-earth pressure curve move horizontally. The soil's internal friction angle and interface angle between the wall have a significant influence on wall displacement-earth pressure curve by changing the active and the passive failure zone behind the wall. The soil stress-strain behavior is microscopic embodiment of the relationship between wall movement and earth pressure, whilst the shape of wall displacement-earth pressure curve and abscissa interval range of wall displacement in the ultimate state are controlled by the soil modulus index and the ultimate shear strain.
  • Experiment on Seepage Characteristics of Unsaturated Soil Under Rainfall Infiltration
    ZENG Ling, LI Guang-yu, SHI Zhen-ning, LIU Deng-sheng, LIU Jie, LI Dong-ke
    China Journal of Highway and Transport. 2018, 31(2): 191-199.
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    A experimental apparatus which was used to measure rainfall infiltration, the matric suction and volumetric water content of the soil under the condition of drainage from the bottom was designed. Indoor model test of rainfall infiltration and drainage on sand and silty clay under different rainfall intensity was carried out. The change law of volumetric water content and the matric suction of the different soil texture under different rainfall intensities were obtained. The results show that, firstly, variation of volumetric water content can be divided into three stages under the condition of rainfall infiltration.The water content at the soil surface increases first and remain unchanged with the infiltration of rainwater, and the water content inside the soil increases from the top to the bottom. When the phreatic line reaches the bottom of model, the water content of the soil begins to increase gradually and transforms from unsaturated state to saturated state. After the soil at the bottom reaches saturated, the water line rises up gradually and each measuring point becomes saturated from the bottom to the top under the action of rainfall. Secondly, volumetric water content of soil surface is proportional to the rainfall intensities. The volumetric water content at the silty clay surface is larger than that of the sandy soil under the same rainfall intensity. The decline rate of the wetting front has a logarithmic function to the rainfall intensity under the condition of rainfall. In specific, the decline rate of the wetting front of sandy soil is larger than that of silty clay under the same rainfall intensity. Thirdly, matric suction decreases gradually from top to bottom with the rainfall infiltration, but the variation of matric suction is not obvious in the process of underground water level rising. Last but not least, volumetric water content of each characteristic point of sandy soil can be fitted by power function, and the silty clay can be fitted by exponential function in the drainage process. The decrease rates of water content in a higher position is faster than that of a lower position.
  • Shaking Table Tests on Dynamic Characteristics of Two-stage Reinforced Soil-retaining Wall（in English）
    CAI Xiao-guang, LI Si-han, HUANG Xin
    China Journal of Highway and Transport. 2018, 31(2): 200-207.
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    In allusion to inadequate researches on multistage reinforced soil-retaining wall, the earthquake performance of two-stage geogrid reinforced soil-retaining wall was investigated by dint of large-scale shaking table tests. The geometric similarity ratios of two-stage geogrid reinforced soil-retaining wall were deduced by Bockingham π theorem. The standard soil was taken as the backfill. The concrete blocks were selected as retaining walls, and the geogrid were regarded as the test model of reinforcements. The characteristics of the wall and the backfill were measured, and earth pressures, displacements of the wall and accelerations of the soil were obtained. The results show that, soil-retaining wall under the action of the earthquake is slanted with the deformation pattern of the buckling and outward bulge. The lateral displacement, the settlements of the top and layered settlements increase with the increase of earthquake peak accelerations. The acceleration of the top of the retaining wall reaches the maximum. With the increase of the input earthquake load, sand flows out from the crevice of the bricks. Subsequently, the top model brick falls down, and the retaining wall is destroyed. The acceleration has amplification effect along the wall height, and the amplification factor of earthquake peak accelerations decrease with the increase of peak acceleration motion. For the lower stage retaining wall, the distribution of horizontal peak dynamic earth pressure along the height is with a large value at the middle and a small value at both ends. For the upper stage retaining wall, with the small earthquake motion input, the distribution of horizontal peak dynamic earth pressure along the height is with a large value at the middle and a small value at both ends. With the large earthquake motions input, the distribution of horizontal peak dynamic earth pressure along height is with a small value at the middle and a large value at both ends. The horizontal peak dynamic earth pressure and horizontal displacement at the top of the lower retaining wall are larger than those at the bottom of the upper retaining wall. The result provides theoretical support for seismic design of two-stage geogrid reinforced soil retaining wall.
  • Observation on Depth and Spatial Effects of Deep Excavation in Soft Clay
    LI Jing-pei, CHEN Hao-hua, LI Lin, MA Ji-shou
    China Journal of Highway and Transport. 2018, 31(2): 208-217.
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    To provide a reference for design and construction of excavation in soft clay, in allusion to the widely existing depth and spatial effects of deep excavation, considering the influence of zoned excavation and diaphragm walls enhancement, the dynamic response of excavation and adjacent environment was investigation the basis of a comprehensive instrumentation program of the third stage excavation engineering at Wufangyuan in Shanghai. The displacement of retaining walls, the axial forces of concrete bracing, the deformation of vertical columns, and the settlements of surrounding pipelines were monitored in site and compared with similar excavation cases. Through the comparison and analysis, the deformation characteristics of excavation, adjacent structures and the effects of excavation depth and construction sequence on excavation in different positions were also discussed. The results show that the excavation exhibit highly spatial and depth effects on diaphragm wall and surroundings. The spatial distribution of excavation during the process of excavation of the shallow soil layer (0~2 m below the ground surface) are mainly affected by the excavation sequence, the soil properties and the concave angle. Deep excavation may cause irreversible wall deflections, where corner effects are significant. The effect of soil creep on the axial force of the first strut is significant, so the axial force keeps continually increasing when the second strut was removed. Since the base slab may help the second strut to resist the pressure of the wall, the axial force of the second strut firstly increase and then decrease when the baseboard is casting. The displacement of diaphragm walls and vertical columns is produced by excavation load. Furthermore, the heaves of vertical columns are greater than those of walls during the excavation because of the smaller distance from the center of the excavation. The settlement rates of the pipelines increase with the increase of the excavation depth.
  • Cyclic Simple Shear Tests on Saturated Soft Clay Subjected to Ellipse Stress Path
    LIU Fei-yu, CHEN Lin, HU Xiu-qing, WANG Jun, CAI Ying
    China Journal of Highway and Transport. 2018, 31(2): 218-225.
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    In order to investigate the influence of horizontal stress on dynamic properties of soft clay, a set of undrained tests with the multi-directional cyclic simple shear apparatus on saturated soft clay were conducted to simulate the horizontal shear stress of soil under the earthquake. Then the influences of phase differences and cyclic shear stress ratios on soil dynamic strain, dynamic pore pressure, dynamic shear strength, deformation characteristics of reconsolidation after shear were analyzed when two-way stress amplitude was 1:2 and phase differences along X,Y direction were 0°, 30°, 60° and 90° respectively, with cyclic stress ration of 0.14, 0.20, 0.25, respectively. The results show that when the cyclic shear stress ratio is small, the shear strain and pore pressure ratios develop slowly and the reconsolidation subsidence is small. When the cyclic shear stress ratio is 0.20, the shear strain and pore pressure ratios increase with the increase of the phase difference. The development of shear strain in Y direction influences the strain in X direction, and the cyclic number of failure decreases with the increase of the phase difference. When the cyclic shear stress ratio is 0.25, the phase difference has little influence on the shear strain, pore pressure and strength. At the same cycle number, the development rate of strain and pore pressure increases with the increase of cyclic stress ratio. Under a certain cyclic stress ratio, the larger the phase difference is, the larger the strain will be. In the meanwhile, the development of the strain along X direction is affected by the strain along Y direction. When the cyclic shear stress ratio is 0.14, the axial deformation is small after the reconsolidation. When the cyclic shear stress ratio is 0.20, the axial deformation increases with the increase of phase difference. When the cyclic shear stress ratio is 0.25, the influence of the phase difference on the axial deformation under reconsolidation can be ignored.
  • Experimental Research on Strength Degradation of Red Sandstone Under Dry-wet Cycle Conditions
    XU Zhi-hua, ZHANG Guo-dong, SUN Qian-cheng, WU Hao, TAN Tai-xi
    China Journal of Highway and Transport. 2018, 31(2): 226-233.
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    The purpose of this paper was to explore the strength degradation properties and damage evolution law of the rock mass in the bank slope drawdown areas under the condition of the reservoir water level fluctuation in cycles. A series of uniaxial and trixial compression tests on red sandstone under dry-wet cycles simulating the actual environment of the water back slope rock mass was carried out. The evolution law of physical properties, especially ultrasonic velocity of red sandstone in dry-wet cycles was analyzed. The influence of the dry-wet cycle on mechanical parameters of red sandstone strength was investigated quantitatively. The damage variable on the basis of cohesion was proposed. The results show that the ultrasonic velocity decreases and the porosity increases with the increasing dry-wet cycles. The trend of variation obviously presents three-stage characteristics. The uniaxial strength of red sandstone decreases with the increase of dry-wet cycles, and the corresponding peak value increases gradually, with the form of brittle failure. The damage variable calculated by ultrasonic velocity show that the damage variable of red sandstone increases nonlinearly with the increase of dry-wet cycles. The power function fitting is applicable to analyze the trend. The cohesion decreases obviously but the friction angle remains steady relatively with increasing dry-wet cycles. The dry-wet cycles reduce the uniaxial strength by weakening the cohesive force of red sandstone. The decreasing percent of uniaxial strength η1N and the decreasing percent of cohesion η2N have high nonlinear relations. The comparison between test and calculated value indicates the rationality of the proposed damage variable based on cohesion.
  • Experiment on Effect of Grass Root System on Slope Soil Strength and Disintegration Characteristics
    WANG Gui-yao, ZHOU Huan, XIA Yi-qi, SHA Lin-chuan, ZHOU Hong-gui
    China Journal of Highway and Transport. 2018, 31(2): 234-241.
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    The erosion resistance of slope plants and slope soil reinforcement usually depended on the enhancement of slope soil strength and its anti-disintegration properties caused by root-soil composites. In order to investigate the influence of grass roots on the strength and anti-disintegration properties of slope soil, ryegrass root growth and its vertical distribution were firstly investigated by dint of the cultivation test and observation. With the direct shear test, the relationship of the strength of root-soil composites, different root content and growth depth for planted roots was obtained. The strength test on root-soil composites with different root content was carried out to compare the strength characteristics of planted and grafted grass roots. In the meantime, disintegration tests on remolded grass-root soil samples and planted grass-root soil samples collected from the highway slope were conducted,and the effect of soil structure and root content on the disintegration characteristics of soil mass was analyzed.The results show that the reinforcement effect of crisscrossing and winding grass roots has significant impact on the enhancement of the strength of root-soil composites. As the capillary root and biological activity exist in the planted grass roots, the reinforcement effect of planted root is far superior to that of grafted root, and the soil strength shows a linear dependence on root content. On account of the reinforcement effect of crisscrossing and winding grass roots, the strength of soil is enhanced, and the pore pressure and closed gas during rainwater infiltration can be reduced by the grass roots in the soil pore penetration.Hence, the grass roots can significantly increase the anti-disintegration properties of the root-soil composites.Due to the structural nature of the cutting slope and a large number of capillary roots derived from the planted main roots, the anti-disintegration properties of original constructional soil are stronger than those of the remolded soil with grafted roots. By replacing grass roots with rice straw in the remolded soil, the strength of root-soil composites and their anti-disintegration properties can be remarkably improved.
  • Experiment on Reinforcement of Jointed Rock Mass by Carbon Fiber Cement-based Composite Material（in English）
    DENG Hua-feng, XIAO Yao, XU Tao, ZHI Yong-yan, DUAN Ling-ling, PAN Deng
    China Journal of Highway and Transport. 2018, 31(2): 242-251.
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    In order to investigate the reinforcement effect, mechanism and the optimum carbon fiber content of carbon fiber cement-based composite material, taking 0, 0.25%, 0.50%, 0.75%, 1.00% as five different kinds of carbon fiber content into consideration, the direct shear test was conducted on the rock specimens before and after reinforcement by dint of the ultrafine cement, fly ash, mineral powder, silica fume and other repair materials. The results show that:the shear stress-shear displacement curves of the jointed rock specimens before and after reinforcement are obviously changed, which are transformed from the absence of peak intensity to peak intensity curves. And there are significant strain softening stages and residual strength stages. With the carbon fiber content increases from 0 to 1.00%, the peak shear strength and residual shear strength of jointed rock specimens under five kinds of normal stress cases increase by 13.0%-54.1% and 0.61%-44.7% respectively. The shear stiffness increases from 32.4% to 216.8%. The cohesion and friction angle of the shear strength parameters increase by 3.4%-20.4% and 127.3%-266.5%, respectively. In comparison, when the carbon fiber content is 0.75%, the comprehensive enhancement effect of the shear resistance after reinforcement is obvious. According to the morphological features of joints and shear failure characteristics after reinforcement, it is found that the cement composite has a good filling and cementation effect on the jointed surfaces. When the carbon fibers are incorporated into the cement matrix, on the one hand, it is similar to "stiffened" material, and the strength and integrity of the slurry can be further enhanced on the basis of pure water slurry to limit the development of micro-cracks during the shear process of the jointed surface. On the other hand, carbon fiber provides a good "anchorage" effect on the sheared slurry, which can further increases the bonding performance of the slurry and the jointed surfaces to significantly increase the shear resistance of the slurry itself and the cementing surface of slurry and jointed surface. Hence, after consolidation, the comprehensive shear resistance of the jointed rock mass can be improved significantly.
  • Model Test on Deformation and Failure of Landslide in Water-level-fluctuating Zone of Three Gorges Reservoir Region（in English）
    ZHOU Chang, HU Xin-li, XU Chu, TAN Fu-lin, WANG Qiang, XU Ying
    China Journal of Highway and Transport. 2018, 31(2): 252-260.
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    In order to clarify the mechanism of deformation and failure in the landslide fluctuation zone, by dint of the physical model test, test models of landslide fluctuation zone based on the geological characteristics of the landslide in the Three Gorges reservoir area was established. The model test material development and the scientific control of the reservoir water level fluctuation made it possible to simulate the whole process of instability of the reservoir landslide fluctuation zone, and the deformation characteristics and mechanical mechanism of the reservoir landslide were discussed from the perspective of the experimentation. The results showed that during the first impounding, the intersecting-angle of cracks is negatively correlated with the inclination of the bedrock. The intersecting-angle determines the direction of the crack propagation and affects the deformation development. The smaller the intersecting-angle is, the longer the crack will be, and the greater the deformation will be.Besides, the hysteretic nature of the water pressure is obvious, and gradually decreases with the increase of the cycle. The fluctuation rate of the water level will shorten the groundwater response time. Furthermore,the greater the water level rate is, the greater the change rate of water pressure in the slope will be.The water level rate has the greatest influence on the underwater slope, which affects the stability of the landslide.Meanwhile,the soil structure deterioration and water floatability is the key factor of the decline of the leading edge of the landslide model.The small landslide is destroyed from the local to the whole under the action of the hydrodynamic pressure and reduced effective stress, showing a typical multi-slip progressive retrogressive mode. The results are helpful in clarifying the mechanism of landslides in water-level-fluctuating zone, and provide the reference for the evolution model and mechanical mechanism of retrogressive landslide triggered by water level fluctuation.
  • Experiment on Spatial and Temporal Evolution of Transient Saturated Zone of Coarse Soil High Embankment Slope Under Rainfall Condition
    HE Zhong-ming, DENG Xi, TANG Hao-long, DUAN Xu-long, BIAN Han-bing
    China Journal of Highway and Transport. 2018, 31(2): 261-269.
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    Based on the similarity theory and the laboratory model test, moisture testers, tensiometers, and earth pressure cells were used to monitor the distribution of volumetric water content, matric suction and forward thrust under the effect of long time heavy rainfall and short time rainstorm. The spatial and temporal evolution law of transient saturated zone of coarse soil high embankment slope under the conditions of long time heavy rainfall and short time rainstorm was investigated. The damage mechanism of coarse soil high embankment slope at the transit saturated zone was revealed. The results show that, at the beginning of rainfall, transient saturated zone mainly appears on slope surface. Volumetric water content increases layer by layer and matric suction dissipates accordingly. With the rainfall going on, affected by long time heavy rainfall, transient saturated zone mainly presents the form of "S". The volumetric water content at the foot of embankment increases and matric suction dissipates firstly. The forward thrust mainly distributes in the depths of the embankment slope. Meanwhile, the shear strength at the foot of embankment slope is more likely to be weakened, and the trend gradually develops into the deep embankment slope. Affected by short time rainstorm, the transient saturated zone mainly presents the form of "J" and distributes near the lower foot of embankment. The volumetric water content near the lower foot of embankment increases and matric suction dissipates firstly. The forward thrust locates on the surface, and then develop into the deep embankment. The weakened area of soil shear strength is distributed on the slope surface and in the lower foot of embankment slope.
  • Model Test of Rainfall-induced Residual Soil Slope Failure
    XU Xu-tang, JIAN Wen-bin, WU Neng-sen, XU Xiang
    China Journal of Highway and Transport. 2018, 31(2): 270-279.
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    In order to investigate the influences of rainfall on deformation characteristics and slope instability mechanism of the residual soil slope, a real-time monitoring system, artificial rainfall system and digital photogrammetry technology were used to conduct a geo-mechanical modeling test under the different location, different slope angles, different density and different rainfall conditions. Then the influence of rainfall infiltration on body displacement and matric suction was observed. Instability risk factor should be considered from the perspective of instability mechanism of landslide induced by rainfall. The variation of the physical quantity of slope should be paid much attention. Three development phases of slope deformation were proposed on the basis of slope deformation and the changing law of matric suction with time. Meanwhile, by dint of instability failure processes under the different conditions, the rainfall-induced residual soil slope failure mode was revealed. The results show that matric suction and body deformation of slope upper part change greatly, and the speed is fast. However, slope lower part soil change slightly with low speed. Compared with the gentle slope with low density, the anti-deformability of the rainfall infiltration in the steep slope with high density is stronger. As the energy required for the small pore structure destruction is much larger than that of the large pore structure, the deformation in the middle part of the gentle slope with low density is larger than that of the upper part of the slope. Considering the law of soil suction, time variation and body deformation, three stages of slope deformation development are put forward, namely, the initial creep stage, accelerated development stage and sliding failure stage. Meanwhile, the slope instability warning factor should be selected from the instability mechanism of rainfall-induced landslides. Besides, the matric suction of slope key position could be selected as the slope instability warning factor for unsupported slope, whilst the change characteristics of matric suction and supporting structure stresses (deformation) should be considered together as the instability warning factor selection for supported slope. Based on the failure process of the soil slope subjected to rainfall infiltration, the failure mode is observed. It starts from slope surface scouring, and gradually develops into gully erosion. Subsequently, the local failure at the slope toe occurs, and the damage scope extends vertically and horizontally and finishes with a global shallow landslide. The depth of slip surface is 1 to 3m, and this kind of landslide should focus on the slope protection to reduce possibility of slope progressive failure as much as possible. The results provide the reference for constructing a prediction model of landslides induced by rainfall in the southeast coastal areas.
  • Research on Nonlinear Creep Damage Model of High Stress Argillaceous Siltstone
    LIU Xin-xi, TONG Qing-chuang, HOU Yong, LIU Yu-cheng
    China Journal of Highway and Transport. 2018, 31(2): 280-288.
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    In order to investigate creep damage characteristics of argillaceous siltstone under the high stress, aiming at the creep effect of the surrounding rock of the deep weak roadway and high-steep slope Long-term subjected to high tress, the argillaceous siltstone was graded and incrementally loaded by using the triaxial rheological tester.Based on the results of creep tests, the different damage evolution of high stress argillaceous siltstone in the stages of hardening and softening were analyzed.The hardening stage took the comprehensive creep damage effect influenced by elastic modulus, stress level and stress acting time into consideration.In the softening stage, the creep damage evolution characteristics of muddy siltstone under high stress were analyzed based on the principle of damage mechanics.The damage evolution equation of high stress and argillaceous siltstone under the influence of different factors was established, and finally the nonlinear creep damage constitutive model was established according to its creep characteristics.Then improved creep model parameters were identified and retrieved.The results show that the creep of high stress muddy siltstone reflects obviously nonlinear characteristics,and the creep hardening and softening characteristics are also obvious.The creep damage variable in the hardening stage increases with the increase of the stress level, and tends to be stable with the increase of time.The creep damage factor increases with the stress level and time in the softening stage.Thus, the creep of high stress and argillaceous siltstone at different stages shows a significant positive correlation with the impact of stress level and stress time.It is shown that the model can better reflect the influence of stress level and time effect on the creep damage characteristics of high stress argillaceous siltstone.The test curves are in good agreement with the theoretical model,and provide theoretical guidance for the support of deep stress chamber and roadway surrounding rock of high stress muddy siltstone.
  • Equivalent-time-line Model of One-dimensional Shear Rheology for Caly(in English）
    HU Ya-yuan, XIE Jia-qi
    China Journal of Highway and Transport. 2018, 31(2): 289-297,318.
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    In order to reveal the rheological characteristics for clay under variable shear stress, an elastic viscoplastic model of one-dimensional shear rheology was established. The shear strain rate was divided into elastic shear strain rate and viscoplastic shear strain rate by dint of the modeling ideas of equivalent time rheological model proposed by Yin and Graham. The elastic shear strain rate had no relation with loading path and was simulated by a non-linear function. As to the viscoplastic shear strain rate, the fundamental equation of viscoplastic shear strain, equivalent time and shear stress was deduced on the basis of Singh-Mitchell empirical formula of the creep rate under the action of constant shear stress. In terms of equivalent time method proposed by Yin, et al, the relational expression was put into the empirical formula of the creep rate. Subsequently, the viscoplastic shear strain rate was obtained, taking shear stress and shear strain as variables. The sum of elastic shear strain rate and viscoplastic shear strain rate formulated the equivalent time lines constitutive relation of one-dimensional shear rheology. The comparison was drawn among the multi-stage loading test of silt clay, the loading-unloading test of loess and the shear strain expressions of this constitutive relationship correspondingly to verify the applicability of this model under variable shear stress. The research results show that the prediction curves obtained by this model are in good agreement with the test curves of the multi-stage loading test and loading-unloading test, which indicate that the model has good applicability under variable shear stress loading. The good predictability of the model also shows that the equivalent time method used in this model is not only suitable for one-dimensional compressional rheology, but also applicable to one-dimensional shear rheology, which expands applied range of the equivalent time method.
  • Influence of Freeze-thaw Cycling on Mechanical Properties of Silty Clay and Ducan-Chang Constitutive Model(in English)
    HU Tian-fei, LIU Jian-kun, CHANG Dan, FANG Jian-hong, XU An-hua
    China Journal of Highway and Transport. 2018, 31(2): 298-307.
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    In order to describe the change rule of the undrained shear behavior of compacted clay under the freeze-thaw cycling, an improved constitutive model which reflected the influence of the freeze-thaw cycling based on the traditional Duncan-Chang model was put forward. A set of freeze-thaw cycling tests were conducted on samples which were made of silty clay from the Qinghai-Tibet Plateau, and unconsolidated undrained triaxial tests were subsequently carried out on the freeze-thaw expansive samples. Besides, the change rule of the parameters of Duncan-Chang constitutive model with the number of freeze-thaw cycles and its corresponding regression relation were determined by stress-strain relations. The stress-strain relations were obtained by dint of triaxial compression tests, on the basis of Duncan-Chang hyperbolic model. Finally, based on the functions of model parameters, the improved Duncan-Chang constitutive model taking the number of freeze-thaw cycles as influence factors was established, whilst a corresponding calculation program for the improved Duncan-Chang constitutive model was drawn up. The results show that the stress-strain curves of samples with silty clay are curves of strain hardening type. The failure strength decreases with the increases of the number of freeze-thaw cycles, and the deterioration effect of the freeze-thaw cycling gradually decreases with the increase of the confining pressure. Among the Duncan-Chang model parameters, the shear strength index, initial tangent modulus, ultimate deviatoric stress, and K all keep decreasing by the increasing number of freeze-thaw cycles, and all parameters can be fitted by the Logistic function. The failure ratio keeps increasing with the increasing number of freeze-thaw cycles, and can be fitted by the ExpAssoc function. The n decreases at first and then increases with the increase of freeze-thaw cycles, and it can be fitted by cubic polynomial function. The calculated stress-strain curves are identical with measured ones, so this improved model is appropriate to describe the variation characteristics of silty clay deformation and mechanical properties under different number of freeze-thaw cycles.
  • K-G Model of Bioenzyme-treated Expansive Soil Based on Disturbed State Theory
    WEN Chang-ping
    China Journal of Highway and Transport. 2018, 31(2): 308-318.
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    A modified K-G model based on disturbed state theory (DST) was proposed to investigate the nonlinear elastic constitutive relation of bioenzyme-treated expansive soil. The isotropic consolidation drainage tests and triaxial consolidated drained shear tests with constant p of remolded expansive soil samples under different ratios of bioenzyme were conducted, and the stress-strain relationship of bioenzyme-treated expansive soil was investigated. The influence mechanism of the ratio of bioenzyme on the tangent bulk modulus Kt and tangent shear modulus Gt of expansive soil was analyzed based on nonlinear K-G model. In order to accord with the actual deformation process, and describe the nonlinear stress-strain relationship of bioenzyme-treated expansive soil more reasonably, based on tests and DST, the disturbance function was defined by taking the ratio of bioenzyme as a disturbance parameter, and a modified K-G model based on DST was put forward to reflect the disturbed effects of the ratio of bioenzyme on the stress-strain relationship of bioenzyme-treated expansive soil. The results show that, according to the comparison among experimental curves, K-G model curves and modified K-G model curves of εv-p and εs-q, the predicted value of bulk strain εv by K-G model is smaller than the test value, whilst the predicted value of shear strain εs is larger than the test value. Both the predicted values of bulk strain εv and the shear strain εs by modified K-G model agree well with the test values respectively. The physical meaning of all kinds of parameters of the modified K-G models clear, and the test methods for determining the parameters in the modified K-G model are the same as that in the K-G model. The deformation characteristics of expansive soil under the different ratio of bioenzyme-based soil stabilizer can be reasonably described by the modified K-G model.
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