Coefficient Of Lateral Earth Pressure Research Articles

Effects of freezing and thawing on retaining wall with changes in groundwater level

Freezing and thawing of pore water within backfill can affect the stability of retaining wall as the phase change of pore water causes changes in the mechanical characteristics of backfill material. In this study, the effects of freezing and thawing on the mechanical performance of retaining wall with granular backfill were investigated for various temperature and groundwater level (GWL) conditions. The thermal and mechanical finite element analyses were performed by assigning the coefficient of lateral earth pressure according to phase change of soil for at-rest, active and passive stress states. For the at-rest condition, the mobilized lateral stress and overturning moment changed markedly during freezing and thawing. Active-state displacements for the thawed condition were larger than for the unfrozen condition whereas the effect of freezing and thawing was small for the passive condition. GWL affected significantly the lateral force and overturning moment (Mo) acting on the wall during freezing and thawing, indicating that the reduction of safety margin and wall collapse due to freezing and thawing can occur in sudden, unexpected patterns. The beneficial effect of an insulation layer between the retaining wall and the backfill in reducing the heat conduction from the wall face was also investigated and presented.

Study on In Situ Stress Distribution Law of the Deep Mine: Taking Linyi Mining Area as an Example

The variation of the in situ stress state is closely related to various factors. In situ stress state is also an important indicator to guide mining production. The study of in situ stress measurement and its distribution characteristics has always been a basic and very important work in mine production. In this study, the deep mines of Linyi Mining Area were considered as the research object. In this regard, the stress distribution law of each mine was studied. We found that the relationship between principal stresses was σH > σv > σh, which belongs to the strike‐slip stress regime. In this stress regime, the lateral Earth pressure coefficient was greater than one, and the magnitude of the three principal stresses all showed an increasing trend with the increase of depth. The maximum horizontal stress direction of the Gucheng Coal Mine, Guotun Coal Mine, and Pengzhuang Coal Mine was NW‐SE under the influence of regional geological structure, while the maximum horizontal stress direction of Wanglou Coal Mine was NE‐SW under the influence of local geological structure. Besides, the relationship between mine in situ stress and mine geological structure, the impact of original rock stress on stope stability, and the effect of original rock stress on floor water inrushing were also investigated. We believe that the research results are beneficial to mine disaster prevention and safety production.

Effects of Pore Water Volume on K0 for Sand Subject to Freezing and Thawing

AbstractIn this study, the coefficient of lateral earth pressure at rest (K0) for sand subject to freezing and thawing was investigated, focusing on the effect of pore water volume. Unfrozen (UF), ...

New analytical solutions for shallow cohesive soils overlying trench voids under various slip surfaces

This paper investigates the effects of cover ratio and soil strength parameters (cohesion and friction angle) on the failure mechanisms of cohesive soils overlying trench voids using trapdoor technique. Adaptive finite element limit analyses (AFELA) were conducted to study the failure mechanisms of trapdoors covered with soils of different thicknesses, cohesions and friction angles. It was found that slip surfaces in the cover soil could be in the shape of vertical, trapezoid, spiral or arching, depending on the combination of soil strength parameters and cover ratio. Analytical solutions under various slip surfaces, considering major principal stress trajectories to describe load transfer paths, were further proposed to study the load transfer mechanisms in shallowly embedded trapdoors. The solutions in terms of arching ratios and lateral earth pressure coefficients were validated against the results of previously reported laboratory tests and AFELA. The results show that the modified earth pressure coefficient is greater than 1.0 due to the consideration of the major principal stress trajectory. The vertical stresses acting on trapdoors are in an inverted parabolic distribution, which are lower in the middle. The arching ratio decreases with increasing soil cohesion, friction angle and cover ratio. For cohesionless soils, the arching ratio decreases as the surcharge loading ratio increases, but for cohesive soils, the arching ratio increases with increasing surcharge loading ratios.

Numerical Analyses of the Optimum Length for Stone Column Reinforced Foundation

The paper presents 3D numerical simulations that investigate the settlement performance for small groups of stone columns under a rigid circular footing. Particular consideration is given to the effects of stone column installation and load level on the optimum length of the stone columns. The results show that taking into account the installation effect by increasing the lateral earth pressure coefficient of the soil reduces the deformation of the columns and the surrounding soil. This leads not only to a reduction in the settlement of the footing but also to a reduction in the optimum length of the stone columns. This optimum length of columns is not constant, it increases with the increase in the load applied to the footing. However, overestimating the installation effect has a negligible consequence on the footing settlement and the optimum length of columns. In addition, the study shows that, for loads exceeding the working load levels of unreinforced soil, the optimum length of the columns is controlled by the extent of the total shear strains beneath the footing evolving with the applied load.

Rigorous lower and upper bounds for the 3D passive earth pressure problem

With the advent of advanced numerical methods, the three-dimensional (3D) passive earth pressure problem has received increasing attention within the last two decades. However, narrow brackets for the exact solution obtained via lower and upper bound simulations have not been presented. In this study, finite-element limit analysis is utilised to determine rigorous bounds for the 3D passive earth pressure problem. A parametric study accounting for different wall geometries, friction angles and wall friction ratios is performed and results are presented in terms of lateral earth pressure coefficient, Kpγh. The results of the lower and upper bound analyses show that in all analysed cases, the exact solution is bracketed within a very narrow range. Furthermore, comparison with existing approaches reveals that, in general, a good agreement is achieved between the current results with data from literature. Furthermore, both lower and upper bound have been improved, especially for narrow geometries, large friction angles and large wall friction ratios.

Active Earth Pressure of Limited C-φ Soil Based on Improved Soil Arching Effect

For c-φ soil formation (cohesive soil) of limited width with ground surface overload behind a deep retaining structure, a modified active earth pressure calculation model is established in this study. And three key issues are addressed through improved soil arching effect. First, the soil-wall interaction mechanism is determined by considering the soil arching effect. The slip surface of a limited soil is proved to be a double-fold line passing through the retaining wall toe and intersecting the side wall of the existing underground structure until it reaches the ground surface along the existing side wall. Second, the limited width boundary is explicated. And third, the variation in the active earth pressure from parameters of limited c-φ soil is determined. The lateral active earth pressure coefficient is nonlinear distributed based on the improved soil arching effect of the symmetric catenary curve. Furthermore, the active earth pressure distribution, the tension crack at the top of the retaining wall and the resultant force and its action point were obtained. By comparing with the existing analytical methods, such as the Rankine method, it demonstrates that the model proposed in this study is much closer to the measured and numerical results. Ignoring the influence of soil cohesion and the limited width will exponentially reduce the overall stability of the retaining structure and increase the risk of accidents.

Experimental modeling of strip footing adjacent to non-yielding retaining wall

A series of reduced-scale models were tested to assess the performance of non-yielding basement wall due to strip footing constructed adjacent to it. Construction design parameters such as strip footing width (B), its distance from non-yielding wall back (a), and footing embedment depth below the backfill surface (df) have been considered in this study. This paper presents results of five model tests that isolate effects of non-yielding wall on the strip ultimate footing bearing capacity. The opposite effect of the strip footing distance design parameters on the non-yielding wall responses is also investigated. Experimental results revealed that the strip footing load-carrying capacity increased, and the settlement decreased as its distance from the back of non-yielding wall increased. Furthermore, the vertically loaded strip footing imposed significant vertical and horizontal forces at the back of the non-yielding wall. Results also indicate that distance a > 4B between the footing and the back of the wall enabled the strip footing to mobilize ultimate load-carrying capacity comparable to both control strip footing test and value calculated with Terzaghi’s equation. Comparison of the measured and predicted lateral forces showed that using elastic theory method together with Jacky formula for at-rest lateral earth pressure coefficient led to about 23–35% underestimation of the measured lateral forces. However, including sand overconsolidation ratio, OCR = 2 resulted in an overestimation of the lateral forces by about 20–29% of the measured value. Finally, results of the experimental program are used to identify sources of conservativeness and non-conservativeness in the current design methodologies used to calculate lateral forces imposed on non-yielding walls due to adjacent strip footing and suggested necessary modifications.

Influence of mechanical properties on the coefficient of lateral earth pressure at rest of frozen soils

In this paper, a theoretical expression of the coefficient of lateral earth pressure at rest (K0) for frozen soils is deduced based on a rate dependent model considering the time related parabolic strength envelope. The deduced expression is then verified with the test results of a fine-grained frozen soil. Comparison of calculated and testing results indicated that the characteristics of strength envelope is crucially important for the accuracy in K0 calculation; while it has little influence on the nonlinear increase tendency of K0 with axial stress. Further analysis shows that, with changes of parameters other than the strength envelope characteristics, the elastic solution of K0 is a limit of K0 calculated from the model. It is also found that the generally accepted empirical relationship between effective angle of internal friction and K0 for unfrozen soil is not applicable for the investigated frozen soil.

Evaluating the overconsolidation ratios and peak friction angles of granular soil deposits using noninvasive seismic surveying

The main objective of this study was to propose an approach to estimate the peak friction angles of over-consolidated granular soil deposits by using the P-wave velocity and the SV- and SH-wave velocities. To this end, seventeen pairs of P- and S-wave seismic refraction profiles were carried out at three different granular sites in Iran using noninvasive seismic wave methods. To estimate the overconsolidation ratio (OCR) in granular geomaterials in terms of SH/SV velocity ratios, a general regression analysis was performed on the obtained data from this study combined with those reported in the literature. In addition, by assuming cross-anisotropy of the soils, the P- and S-wave velocities were utilized to develop an equation for calculating the coefficient of lateral earth pressure at rest (K0). The Mayne and Kulhawy formula was finally employed to evaluate $$\varphi^{\prime}$$ in granular soil deposits by combining the calculated K0 values and the estimated OCR values. The findings of this study may be used as the appropriate approaches for economic and noninvasive determination of in-situ peak friction angle in granular soil deposits using the surface seismic surveying.

Compressibility behavior and lateral earth pressure of a marine soil mixed with tire crumbs

The reuse of scrap and by-product materials in civil engineering applications has increased in recent years due to environmental considerations. Soil-tire mixtures can be used in land reclamation in marine areas. The effects of tire crumbs on the compressibility behavior of a calcareous soil are evaluated in this study. Calcareous soils are generally located in tropical and semi-tropical areas near important strategic industries such as the Persian Gulf. In this study, the modification of effective stress theory for Qeshm calcareous soil-tire crumbs mixtures is investigated by using a tall oedometer apparatus. The effects of the compressible material on the lateral earth pressure coefficient of the mixtures are also studied. The results show that the tire crumbs have an influence on the overall compressibility of the mixtures. Increasing TC content results in decreasing the lateral earth pressure. In mixtures with 30% of tire crumbs K0 is reduced by approximately 110% and 66% in loose and dense samples, respectively. The increase in vertical stress reduces the effects of tire crumbs on soil-tire mixtures. The particle breakage of the mixtures is also decreased at a rate of about 0.06% per 10% of tire crumbs.

ВЛИЯНИЕ ГЕОМЕТРИЧЕСКИХ ПАРАМЕТРОВ ОТКОСОВ И УСТУПОВ ГРУНТОВЫХ ВЫЕМОК НА ИХ УСТОЙЧИВОСТЬ

The paper presents the results of studying the influence of the slope angles of ledges and slopes on their mutual stability. The values of the slope stability coefficients are determined depending on the slope angle of the ledges, as well as the values of the stability coefficients of each ledge depending on the slope angle and the location of the ledge on it. Evaluation of stress-strain state of the soil and determination of the coefficients of stability (definition of the forms and provisions, the most probable sliding surfaces) are carried out by computer simulation using the finite element method and taking into account the value of the coefficient of lateral earth pressure. Various combinations of ledge heights and slope angles are considered, and it is found that the maximum difference between the stability coefficients of straight and two-stage slopes is observed in the case when the lower ledge has the highest height and slope angle. The upper ledge can be considered isolated. The stability of the lower ledge for each of the considered options depends on its angle of inclination and the angle of inclination of the upper ledge. Thus, it is found that it is possible to choose such combinations of values of the slope angles of their ledges and heights, when designing slopes, with which their stability will be the maximum one. When designing various structures on the slopes, the selection of these geometric parameters helps to correctly plan the work on leveling the shape of natural slopes or creating embankments in such a way that it will have a significant impact on improving their operational reliability.

Measurement and Correlations of K0 and Vs Anisotropy of Granular Soils

The coefficient of lateral earth pressure at rest (K0) and stress-dependent shear wave velocity (Vs) of granular soils under one-dimensional compression loading were measured using a modified float...

Seismic loading on cantilever retaining walls: Full-scale dynamic analysis

The assessment of realistic seismic loading on cantilever retaining wall requires modeling of actual seismic events to act on an integral cantilever wall. In this sense, an analysis is carried out to simulate eight candidate earthquake time histories. Scaling effect on seismic motions is taken into consideration through a one-dimensional numerical calculation using SHAKE2000 software. Two-dimensional PLAXIS finite element analysis is carried out through a full-scale seismic analysis of a typical cantilever retaining wall. Results of the analysis quantified seismic earth pressure in terms of magnitude and point of application. These results are presented in a non-dimensional chart to be compared with up-to-date seismic loading propositions. In conclusion, a relationship is proposed to relate the horizontal seismic inertial coefficient with a representative lateral seismic active earth pressure coefficient.

Behavior and Design of Back-to-Back Walls Considering Compaction and Surcharge Loads

Back-to-back geosynthetic-reinforced retaining walls are commonly used as approach embankments for bridges and flyovers. Compaction and surcharge loads should be incorporated in the model to understand the realistic behavior of mechanically stabilized earth (MSE) retaining walls through numerical modeling. In this study, a finite-difference method-based numerical model, Fast Lagrangian Analysis of Continua (FLAC 2D, Version 7.0), is used to study the effects of surcharge and compaction stresses on lateral pressures and lateral displacements of back-to-back MSE walls. The ratio of the distance between walls to the height of the wall (W/H) in back-to-back walls is varied from 1.4 through 2.0, and the stiffness of reinforcement from 500 to 50,000 kN/m to cover the entire range of stiffness values of extensible to inextensible reinforcements. The coefficient of lateral pressure, Kr, at the end of the reinforcement zone for W/H = 1.4 is found to be 50% less than that for W/H = 2.0. Plots showing the variation of lateral earth pressure coefficients and lateral deformations versus normalized depth of wall are presented. Maximum tensile forces in the reinforcements along the depth of wall are also analyzed. The lateral pressures at the facing appear to be unaffected with W/H ratio. Finally, a design example showing the external stability analysis of reinforced back-to-back walls is illustrated incorporating the lateral pressures obtained from the study.

On evolving size and shape of gas bubble in marine clay under multi-stage loadings: microcomputed tomography (μCT) characterization and cavity contraction analysis

Discrete bio-gas bubbles commonly form in fine-grained marine sediments and have modified many aspects of the behavior of these sediments, including strength, stiffness, and permeability. Although the level of such modifications is known to govern by bubble shape and size, limited studies have been undertaken, mainly due to difficulty in nondestructively characterizing bubbles within a soil under in situ stresses. In this study, a mini-loading device was developed to perform one-dimensional loading tests on gassy marine clay and gassy silt in a microcomputed tomography (μCT). The evolving bubble shape, size, and pressure during loading were quantified, and the resulting stress fields around the bubble cavities were evaluated via elliptical cavity contraction analysis considering stress anisotropy. As the vertical load increased, bubble cavities were found to compress predominantly along the vertical loading direction, with little horizontal compression, because localized soil failure (LSF) and thus cavity collapse occurred mainly near the roof of the at-rest lateral earth pressure coefficient (K0)-stressed elliptical bubble cavities. The evolution of bubble shape and size under loading is significantly affected by stress anisotropy, which governs the extent and location of the LSF. A Gaussian mixture model is adopted to quantify the evolving distributions of bubble structure parameters, which are essential for developing more physically rigorous gassy soil models.

A spectral multidomain penalty method solver for the numerical simulation of granular avalanches

This work presents a high-order element-based numerical simulation of an experimental granular avalanche, in order to assess the potential of these spectral techniques to handle conservation laws in geophysics. The spatial discretization of these equations was developed via the spectral multidomain penalty method (SMPM). The temporal terms were discretized using a strong-stability preserving Runge-Kutta method. Stability of the numerical scheme is ensured with the use of a spectral filter and a constant or regularized lateral earth pressure coefficient. The test case is a granular avalanche that is generated in a small-scale rectangular flume with topographical gradient. A grid independence test was performed to clarify the order of the error in the mass conservation produced by the treatments here implemented. The numerical predictions of the granular avalanches are compared with experimental measurements performed by Denlinger & Iverson (2001). Furthermore, the boundary conditions and parameters such as lateral earth pressure coefficients and the momentum correction factor were analyzed to observe the incidence of these features when solving the granular flow equations. This work identifies the benefits and weaknesses of the SMPM to solve this set of equations and, it is possible to conclude that the SMPM provides an appropriate solution of the granular flow equations proposed by Iverson & Denlinger (2001). Besides, it produces comparable predictions to experimental data and numerical results given by other schemes.

Lining performance optimization of sub-rectangular tunnels using the Hyperstatic Reaction Method

Sub-rectangular tunnel cross-sections are commonly used in underground engineering projects. However, very limited studies have dealt with the design of this kind of non-circular tunnels. In this paper, taking a twin-lane metro tunnel as an example, the optimization process of sub-rectangular tunnels in terms of tunnel lining forces is presented using the Hyperstatic Reaction Method (HRM). A series of mathematical functions considering the tunnel shape are used and the optimization of sub-rectangular tunnels shape is deduced. The effect of different parameters, such as the coefficient of lateral earth pressure at rest K0, Young’s modulus Es of soil, tunnel depth C, surface loads P0 on the internal forces and shape of sub-rectangular tunnel is then investigated.

Three-dimensional stress-transfer mechanism and soil arching evolution induced by shield tunneling in sandy ground

Tunnel excavation inevitably causes variations in stress and displacement fields in soil, which could affect the serviceability and safety of the adjacent underground structures. Change of the earth pressure acting on the existing structures is closely related to soil arching effect caused by a new tunnel excavation, but it is still lack of full understanding. In this study, a finite element method (FEM) model was first verified by field measurements based on a case history of Metro Line 2 construction in Changsha, China. Then, a series of simplified three-dimensional (3D) FEM models were established to investigate the stress redistribution and the soil arching evolution induced by earth pressure balance shield (EPBS) tunneling. The changes of the earth pressure, the coefficient of lateral earth pressure, and the settlement of soil mass above the tunnel during tunneling were analyzed and the soil arching zone was determined. 3D stress-transfer mechanism in soil arching zone during tunneling was revealed. In addition, the influences of shield-driving parameters (i.e. support pressure, grouting pressure) on soil arching evolution were also investigated. The results show that the loosened zone extends to nearly 0.73D (D = tunnel diameter) above the tunnel crown in vertical direction. The height of the arch zone above the loosened zone is about 1.27D. The horizontal soil arching in front of EPBS occurs near the ground surface. With EPBS advancing, the horizontal soil arching gradually transforms into the vertical soil arching. After the installation of lining, the earth pressure is finally mainly transferred by vertical soil arching in the transverse section. The proper combination of shield-driving parameters for controlling the expansion of the loosened zone is support pressure of 0.6P1 − 2.2P1 and grouting pressure of 1.0P2 − 1.8P2, where P1 is initial horizontal stress at the tunnel axis and P2 = 1.2P1.

Model Studies of Lateral Soil Pressure on Drilling Piles in Dry and Saturated Sands

The results of a model study of single piles shaft bearing capacity in dry and saturated sandy soils are presented. The effect of loading rate on pile shaft capacity was investigated. The shaft bearing capacities of the piles were determined by pile load tests and compared with theoretical results. Generally, pile shaft capacities are greater than the theoretical values. The lateral earth pressure coefficient K depends on the internal friction angle of the soil, the pile diameter, the effective stress, and the saturation degree of the soil. It is shown that K decreases as the pile length/ diameter ratio increases.