Slope Stability and Earth Retaining Walls

Rainfall infiltration is an important factor affecting slope stability. To investigate the influence of rainfall on highway slope stability, a typical cut slope of highway in rainy region has been adopted for the study. Based on saturated - unsaturated seepage theory and coupled solid-liquid analysis, the features of seepage, pore-water pressure, stress and displacement of the highway slope are analyzed under two different rainfall intensity and duration conditions. At the same time, modified Mohr-Coulomb strength criteria and 2-D limit equilibrium method are used to calculate the safety factors of the slope. The results showed that the range of unsaturated zone decreased, while the transient saturated zone enlarged, the pore-water pressure, displacements and the negative shear stress on the surface of the slope rose with increasing rainfall intensity and duration. The safety factors of the slope also decreased with rising of the rainfall intensity and duration and were all lower than 1.0. To mitigate, anchor-shotcrete reinforcement with adhesive bolt suspended net was applied to the slope. The results from field monitoring showed that the reinforced slope is stable even after continuous heavy rain. Therefore, anchor-shotcrete reinforcement is a useful method for strengthening slopes in rainy regions.

The non-associated flow rule was introduced by means of modification shear strength parameters and a kinematically admissible velocity field was considered for slope stability analysis. The effectiveness and validity of the analysis method in this paper was illuminated through a case study. Comparative analysis has shown that the proposed method gives better calculation results. The results show that the consideration of parameters of non-associated flow rule plays a remarkable role on the slope stability. Therefore, the presumption that geomaterials subject to associated flow rule takes disadvantageous influence on evaluating the real stability characteristics of slope.

Stratified rock mass is often encountered in geotechnical engineering applications, and its compressive strength is the main parameter in engineering design. With obvious transversely isotropic characteristic, strength of stratified rock mass is not only related to strength of intact rock but also to the inclination and characteristic of bedding plane. Due to the complicated characteristic of stratified rock mass, the numerical method is used to simulate the uniaxial compressive test, to study the effect of the bedding plane of stratified rock mass to the stress-strain response and strength characteristic of stratified rock mass. The numerical analysis method is based on the analytical solutions, which can simulate geotechnical models with complicated geometry, to obtain stress-strain relationship and failure modes of stratified rock mass.

A typical channel crossing section of the South-North Water Diversion Project, in Shandong Province, China was chosen to carry out slope safety analysis using the finite element based strength reduction method. A revised anisotropic model was applied as a comparison to the original Duncan-Chang nonlinear constitutive models in the FEM analysis to simulate the stress and strain relationship of the soil. A displacement criterion was used to compute the factor of safety. The factor of safety calculated by the strength reduction method was verified by the Bishop method of slices which is one of the traditional limit equilibrium methods of slope stability analysis. The calculated displacements based on both models were compared with measured field displacements. It was found that although the factors of safety calculated through both models are the same, the displacement values calculated by the revised model and the Duncan-Chang models are different. It is suggested that the revised model should be applied in simulating the practical excavation stress path.

In the assessment of slopes, factor of safety (Fs) still remain the primary indexes for determining stability of slopes. Traditional limit-equilibrium techniques are the most commonly-used analysis methods, which consider slope material as rigid body. Recently, however, rapid advances in computer technology and sustained development have pushed the numerical analysis like the method of fast lagrangian analysis of continua three dimensions (FLAC3D) to the forefront of geotechnical practice. In numerical analysis, shear strength reduction method (SRM) is mainly adopted to calculate factor of safety for slopes based on Mohr-Coulomb model. A roadway slope is chosen as the study subject in the present paper. The calculation method of limit equilibrium method and shear strength reduction method are adopted to analyze the stability of the slope. Some useful conclusions are obtained to provide guidance for the real practice.

Bolt is widely used in ground reinforcement engineering such as slope, tunnel or large caves engineering. The traditional steel bolt has some disadvantages, because it may be corroded by groundwater or chemical solutions, which cause the reductions of mechanical strength and service life. Glass fiber reinforced polymer (GFRP) bolt has the good characteristics of lighter weight, higher strength and corrosion-resistance. Those advantages make it a better alternative in some fields of engineering, and attract great attention of many scholars. Based on the Canadian Standards Association (CSA) criterion, pullout test is used to study the bond behaviors of GFRP bolt in cement mortar. Meanwhile, the bond stress of the GFRP bolt along the bolt longitudinal direction is analyzed in theory. The conclusions from the research may shed a light for a more rational design of GFRP anchors.

A three-dimensional finite element limit equilibrium method (3DFLEM) based on the concept of strength reduction and the unique sliding direction is presented. The definition and physical meaning of factor of safety (FOS) as well as the relationship of FOS and the unique sliding direction are clarified. On the basis of mean value theorem of integrals, the FOS corresponding to sliding body of an arbitrary shape is defined. The relationship of partial FOS and overall FOS can be demonstrated by the definition of factor of safety. The results of stability analysis obtained from the proposed approach, 3D rigid limit equilibrium method (3DLEM) and 3D shear strength reduction method (3DSSRM) are compared. It is shown that: 1) the factor of safety and critical sliding surface are generally in good agreement; 2) the element size of slope and sliding surface has certain effect on FOS by causing maximum difference of 2%. However, the effect of yield criterion used in the stress- strain analysis may be negligible.

Block theory regards rock mass structural face as a plane and cutting through whole rock-mass, i.e. joint trace length is infinite, but factually, it is finite revealed by engineering cases. This shows that block theory fails to give a full consideration to joint properties. In this paper, the author properly introduce joints random probability model into block theory to analyze key block slide probability. And make a comparison stability analysis by block theory and modified block theory in a case of rock mass slope. It is also testified that modified block theory is same effective with block theory, and more convenient for engineering application.

This paper presents a study on the influence of the probability distribution curve of shear strength parameters on the reliability analysis of a rock slope. The findings of this investigation is applied a rock slope in Luoyang, China. The probability distribution of shear strength parameters (c and φ) may not follow the normal distribution assumed in most reliability-based analyses. There is a negative correlation between c and φ, which will affect significantly the results of the reliability analyses. In order to study the influence of a probability distribution curve, four different types of distribution curves are used in this study. It is concluded that the failure probability of a rock slope is sensitive to the probability distribution of the shear strength parameters. Based on this study, the failure probability can vary about ten times between two extreme cases where two different distribution curves are used. It is also found that the failure probability increases while the correlation coefficient between c and φ decreases. A sensitivity analysis of the probability distribution curve is suggested for future reliability analyses.

Rainfall-induced fill slope failures have been observed around the world indicating evidences of inadequacy for present slope stability analysis for storm condition. This paper proposes a simple and practical method to evaluate the potential of hydraulic destruction of fill slopes upon wetting. The usefulness of this method was illustrated by comparing the results with an actual case of failure. It was found to give rational results that compare reasonably well with those observed in the field.

In order to guarantee tunnel construction safe, the stability of the front slope at the entrance of tunnel was improved by cutting slope with anchor, jet concrete and steel net. At first, the geological condition of front slope at the entrance of the tunnel was investigated. Then, the mechanism of cutting slope to improve the stability of front slope was analyzed. At last, the angle and configure of cutting slope with alluviation residual soil was simulated. The result was shown that when front slope angle was more than thirty degrees, it was obvious and feasible to improve its stability through cutting slope. When its angle was less than thirty degrees, cutting slope was not feasible. It was result that the safety factor of front slope was more than one point six and it was safe enough to meet the need of tunnel excavation.

The complicated geological structure can be accurately described by using a 3D geological model. If a 3D geological model can be applied to calculate the safety factor of slope through the integration, then the goal to transfer "visualization" to "calculation" can be realized. Through it, the advantages of GIS could be exerted and the purpose that analyzing slope's stability based on the mechanics of the professional analysis could be achieved. The main contents in this paper include: (1) The database of the three-dimensional geological model, and the methods and process of interpolations are introduced. By using the three-dimensional solid model, even profiles of the drilling wells were generated. (2) Considering the drawbacks of the 3D Sarma method, two aspects were modified. First, though the interface of every column satisfies the Mohr-Coulomb's Law, the parameters between the bottom surface and the lateral surface are different. Second, the probability of the lateral and bottom surface are subjected to damage simultaneously is low. (3) The database of 3D geological model was applied to three-dimensional limit equilibrium successfully by programming. (4) Finally, using the GOCAD a three-dimensional geological model of an engineering slope was built as part of the work presented in this paper. Afterward, the safety factor of slopes, by using of the three-dimensional limit equilibrium method in different conditions, such as water loading, earthquake loading, were solved. The calculation results can help us to better understand the slope's stable state.

Applicability of Imbalanced Thrust Force Method (ITFM) is investigated for shear strength parameter back-calculation of red clay slope. Equations are established for "similar" profiles, which possess similar geological conditions and similar sliding status or stage. Combined with the multidimensional chart of cohesion and friction angle, shear strength parameters are finally determined through trial calculation, interpolation and curve fitting. Moreover, research on back-analysis of compound sliding, including integral and sectional back-calculation, was proposed.

Numerical simulation was performed with Flac^3D to study on spatial factors of anchors. For the studied case, factors affecting slope stability with reducing effect are: length of middle level anchors, length of lower level anchors, length of upper level anchors, average elevation of anchors, vertical spacing and inclination of anchors. Displacement mainly occurs in middle-upper part of slope. Maximum tension of anchors appears on the middle level anchors. For the given slope, the best inclination of anchors is suggested to be 17° from horizontal; optimized uniform length of anchors should be 8m. Optimal horizontal spacing of anchors is determined to be 3m. Diamond-shaped layout has better reinforcing effect than rectangular layout. Anchors should be installed without overlap of adjacent reinforcing areas. Unreinforced soil mass should be separated into small blocks by adjusting spacing between anchors so as to achieve the best reinforcing effect.

To select proper strength parameters for slope stability analysis of red clay, study on the influence of dry-wet cycling and water content variation was performed based on direct shear tests. It is found that: (1) shear strength parameters are greatly affected by water content instead of cycling; (2) with the decrease of water content, shear strength increases, especially, relationship curve between cohesion and water content is concluded to be logarithmic; (3) under the same experimental conditions, cohesion and friction angle of hard plastic clay are generally larger than those of soft plastic clay. Dry-wet cycling leads to cracks which are harmful to slope integrity. Slope failure of red clay under dry-wet cycling, appearing to be shallow sliding, is resulted from cracks and water infiltration. Consequently, it can be analyzed with (c_u, φ_u) or (c_cu, φ_cu) of saturated upper layer, as well as taking cracks on potential sliding surfaces into consideration.

Slope stability has been an important issue in geotechnical engineering area. Monitoring of slope movement is the main method for information-based construction. It plays a very important role in slope protection and stability assessment. This paper presented a case study of monitoring of deformation at a slope cut section on the Yu Xiang Expressway. The earth deformation measurement, deep displacement deformation monitoring, geological inspection and other means were used to carry out comprehensive monitoring of the cut slope. Based on monitoring results, the slope was considered stable.

Early detection of areas prone to landslides is a necessary safeguard in order to ensure the safety of people, business and facilities within these regions. This paper focuses on the feasibility of using a Global Positioning System Global (GPS) with a system for Mobile Communication (GSM) to relay land movement to remotely located monitoring modules. The system utilized Simple Messaging Services (SMS protocols) in concordance with postprocessing software to gather and evaluated land movement. Several tests were conducted in Taiwan's Wu Fong Chi district of Ilan. This area is known for landslides. The tests included static and localized simulations along with landslide simulating experiments. Two different distances from the monitoring area to the reference site were assessed. These distances, also known as baselines were evaluated and the differences of accuracy were recorded. Through the usage of Global Systems for Mobile Communication (GSM), the data was successfully conveyed through wireless communication. According to the experiments, the usage of short baseline length promoted both the precision surveying and calculation of the information. Additionally, a Global Positioning Monitoring Systems (GPS) was able to render results for both short and long distance baselines that were within centimeters of accuracy.

Traditional instruments which monitor the slope stability are often installed underground or buried in the ground. Survey of the monitoring points in a slope is normally done using GPS or a level. GPS surveying is efficient, can be used on most of the year except under snow storms and been used worldwide. Comparing with dual-frequency geodetic receivers, the single-frequency receivers are cheaper. If working with single-frequency receivers can maintain reliable readings, the cost will be reduced. In this paper, the ability of single-frequency GPS receivers was checked. First, in the experiments of GPS static surveying, the precision with single-frequency and dual-frequency in a slope survey was compared. It showed that we can achieve reliable reading in a slope area using single-frequency receivers. Finally, the reliability of low-cost receivers with single-frequency was tested in the case of short baseline (less than 5 km). An efficient approach by single-frequency GPS receiver was also suggested in the paper.

The pile and abutment stability introduce a design challenge when highway or railway bridge is constructed within a landslide in mountainous regions or hilly land. Aiming at the deformation of bridge foundation caused by the movement of the landslide, the displacement feature of the pile and the abutment were tracked and measured by setting measuring spots at the bridge pier. Based on the analysis of observed data and theoretical analysis, the paper proposes a combination treatment using prestressed anchor cable and prestressed slide resistant pile, and the method for calculating anchoring force is given. Length of anchor cable and prestress force value are designed base on the results of field testing. Practical application shows that the method is effective and can be referenced in engineering practice.

Based on friction law of single state variable, this paper establishes a nonlinear synergy-bifurcation model to forecast the sliding time of land slope. Then, by using of this model, combining with the displacements in-situ of slope, the sliding time of the slope can be calculated. Especially, the GA improved BP Neural Network is used firstly to forecast part of the future displacement series which can be got a more accurate result being improved by GA, then, using the more accurate future displacement series into the nonlinear synergy-bifurcation model, the sliding time of the slope can be deserved. This nonlinear synergy-bifurcation model belongs to a kind of scroll forecasting method which can avoid the continuing accumulation of forecasting displacement error that leads the forecasting data departing away from the true ones. At last, validated by a real case of slope sliding, the GA improved ANN-synergy-bifurcation model forecasting method can tell a more exact displacements of sliding, as well as work out the sliding time of slope. It can be used to forecast, prevent and rehabilitate the corresponding geo-disasters.

The landslide geohazard frequently occurs in the loess region in Northwestern China. Long distance transportation line project covers through varied Loess plateau geology elements. It endurs landslide infringement. Taking a key locality of the long transportation line project in loess regions as study object in this paper, the research work focuses on regional and monomer landslide forecasting warning models and the landslide monitoring and warning system based on GIS. The emphasis falls on the designing and development of the landslide geological hazard monitoring and warning system in study area. On the basis of prolific geological statistics, the basic spatial data, geohazard thematic data, project data and monitoring data of study area can be impact into the landslide geohazard monitoring and warning system with GIS. The structure and composition of forecasting and warning GIS system are analysized by combining with the study on warning models.

With upgrading Hangzhou-Shanghai Waterway of Beijing-Hangzhou Grand Canal as the background, it is difficult and highly costly to upgrade waterways with traditional shoring methods according to the shortage of land for the Yangtze River Delta region. The feasibility of concrete sheet pile as vertical shoring is studied by finite difference analysis method. Earth pressure, settlement, horizontal displacement of shoring structure and the pile's stress and strain variation are obtained by simulating the design conditions and checking conditions before and after dredging of river channel. A comparative analysis is carried out between field test results and the simulations, which indicates that the medium-or-short thin concrete sheet-pile structure can be used as the shoring structure to upgrade waterways without increasing the width of water surface for its anti-overturning and sliding characters.

The prestressed-dispersed anchor cantilever retaining wall is a novel combined retaining structure. In this paper, the earth pressure distribution, the displacement of retaining wall, force of anchor cable, and the stress of anchor plates were analyzed with finite element method. The analysis results show that, the earth pressure increases linearly along the wall height from top to bottom approximately. The total earth pressure value is between the values of active earth pressure and at-rest earth pressure. The wall displacement of the wall can be reduced effectively with prestressed anchor cable and plate. The structural stability of the retaining wall is also improved. The conclusions in this paper can provide a base for the design and calculation of this kind of retaining wall.

For studying effects of reinforcement distribution modes and distribution density on the stability of the road embankment, the upper-bound method of the limit analysis was employed to compute the critical height of the reinforced soil slope. In analysis, the rigid body rotational failure mechanism was adopted and the failure mode of the reinforcement was assumed to be its own tensile failure. Three types of reinforcement distribution modes, i.e., uniform mode, linearly increasing density mode and linearly decreasing density mode, were considered. With the same average reinforcement density, the critical height of the slope is the maximum for the linearly increasing density mode of reinforcement, and it is the minimum for the linearly decreasing density mode. So it's suggested that reinforcement distribution density in the lower position of the slope should be increased appropriately. For the three types of reinforcement distribution modes, the critical heights all increase obviously with the increase of average reinforcement distribution density. By comparison, the critical heights from upper-bound method were found to be in good agreement with the results of centrifuge model tests.

This paper report a study of the stress and deformation characteristic of a Mechanically Stabilized Earth (MSE) retaining wall constructed on a loess plateau and the development of empirical relationships for the geotechnical parameters required for the design of structures such as earth retaining walls and slopes. Data for this study was acquired during the construction of an instrumented tiered MSE retaining wall in northern Shaanxi province, P. R. China. The data acquired includes the vertical pressure of backfilled soil, the horizontal earth pressure and the strain in the reinforcement strips. Based on the analysis of the acquired data, the following conclusions are made. The value of measured vertical earth pressure increases with the height of the backfill, but the measured values in most cases were smaller than the theoretical values; the distributions of horizontal earth pressure are affected by the location of earth pressure cells and soil properties; measured horizontal earth pressure increases with the height of backfill but are clearly smaller than the Rankine active earth pressure; the horizontal tensile strains on the reinforcement strips come larger with the backfill height; and the distribution rules of strains in the two retaining wall tiers are different. Strain curve on the upper setback shows a single peak distribution , while it on the lower portion of retaining wall shows double-peak distribution. Measured failure surface is similar with Rankine failure surface but comparatively different with "0.3 H Approach" line in the Code for design on retaining engineering structures of railway subgrade of China.

In the paper, through finite element three-dimensional numerical simulation, deformation and internal force variation of double-row piles composite gravity arch supporting system has been analyzed with changing key design parameters such as double-row pile diameter, distance between rows, arch height and arch thickness. Optimization design analysis has also been carried out for this new supporting system. Results show that appropriate increasing pile distance can be used to decrease lateral displacement of supporting system, but it should not be increased blindly for supporting effect. Otherwise the determination method of optimal arch height and thickness values are also put forward in the paper.

A multi-shear mechanism plasticity model is defined in strain space to simulate pore pressure generation and development in sand under cyclic loading and undrained conditions in the paper. The seismic horizontal deformation of typical caisson quay are analyzed in detail by the plasticity model under different engineering situations. An index of liquefaction extent is applied to describe the pattern of residual horizontal deformation of quay top under different engineering situations. Some prediction equations are derived from the F-E analysis results between residual horizontal deformation and extent of liquefaction in the relative safe soil site. Then, the reasonableness and the reliability of the derived prediction equations are validated by a 1g shaking table test results.The comparison results show when the unit weight of quay is relatively lower, the predicted value is better by the application of high liquefaction extent and even regressive equation, and when the unit weight of quay is relatively higher, the predicted value is better by the application of high liquefaction extent and broad band regressive equation of lower curve.