The lateral pressure coefficient at rest of expansive soils in landfill at various vertical stresses and moisture contents

When expansive soils in the original location are artificially transferred to landfill in different seasons,and subject to engineering activities afterwards,the corresponding deformation and stability of retaining structures become unpredictable.This necessitates the determination of lateral pressure coefficient at rest(k_(0) value)for expansive soils in landfill.Considering compaction,excavation of expansive soils,as well as construction of landfill in different seasons,series of stepwise loading and unloading consolidation tests at various moisture contents were carried out in this work to explore the evolution characteristics of k_(0) value and assess the dependence of k_(0) value on vertical stress and moisture content.Besides,scanning electron microscope(SEM)was used to track the change in microstructural features with vertical stresses.The results indicated that the k_(0) value of expansive soil shows a pronounced nonlinearity and is inextricably linked with vertical stress and moisture content,based on which a prediction formula to estimate the variation in k_(0) value with vertical stress during loading stage was proposed;there is a significant exponential increase in k_(0) value with overconsolidation ratio(OCR)during unloading stage,and OCR dominates the release of horizontal stress of expansive soil;SEM results revealed that with an increase in vertical stress,the anisotropy of expansive soil microstructure increases dramatically,causing a significant directional readjustment,which is macroscopically manifested as an initially rapid increase in k_(0) value;but when vertical stress increases to a critical value,the anisotropy of microstructure increases marginally,indicating a stable orientation occurring in the soil microstructure,which causes the k_(0) value to maintain a relatively stable value.

At-rest lateral earth pressure of compacted expansive soils:Experimental investigations and prediction approach

This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between theσL and the vertical stressσV during soaking and consolidation,(ii)the influences of initial dry densityρd0 and moisture content w 0 on the vertical and lateral swelling pressures at no swelling strain(i.e.σV0 andσL0),and(iii)evolution of theσL during five long-term wetting-drying cycles.Experimental results demonstrated that the post-soakingσL-σV relationships are piecewise linear and their slopes in the passive state(σL>σV)and active state(σL<σV)are similar to that of the consolidationσL-σV relationships in the normal-and over-consolidated states,respectively.The soakingσL-σV relationships converge to the consolidationσL-σV relationships at a thresholdσV where the interparticle swelling is restrained.TheσL0 andσV0 increase monotonically withρd0;however,they show increasing-then-decreasing trends with the w 0.The extent of compaction-induced swelling anisotropy,which is evaluated byσL0/σV0,reduces with an increase in the compaction energy and molding water content.TheσL reduces over moisture cycles and the stress relaxation in theσL during soaking is observed.An approach was developed to predict the at-rest soakingσL-σV relationships,which requires conventional consolidation and shear strength properties and one measurement of theσL-σV relationships during soaking.The proposed approach was validated using the results of three different expansive soils available in the literature.

Prediction and safety analysis of additional vertical stress within a shaft wall in an extra-thick alluvium

An alluvium with a sandy aquifer at the bottom,but lacking an effective impermeable layer between the sandy aquifer and bedrock is referred to as a special alluvial stratum.Impacted by the drainage of the aquifer due to mining activities,a shaft wall in this special alluvial stratum will be subject to a downward load by an additional vertical force which must be taken into consideration in the design of the shaft wall.The complexity of interaction between shaft wall and the surrounding walls makes it extremely difficult to determine this additional vertical force.For a particular shaft wall in an extra-thick alluvium and assuming that the friction coefficient between shaft wall and stratum does not change with depth,an analysis of a numerical simulation of the stress within the shaft wall has been carried out.Growth and size of the additional vertical stress have been obtained,based on specific values of the friction coefficient,the modulus of elasticity of the drainage layer and the thickness of the drainage layer.Subsequently, the safety of shaft walls with different structural types was studied and a more suitable structural design,providing an important basis for the design of shaft walls,is promoted.

An Experimental Study on Distribution of Vertical Stress in a Silo with a Central Inner Downcomer

The distribution of vertical stress for both active and passive state in the silo with a central innerdowncomer is reported in this paper. Experimental measurement of the axial distribution of vertical stress for bothactive and passive state in the silo are in good agreement with that predicted by theoretical analysis. The meanaxial stress is reduced due to the presence of the inner downcomer in the silo.

One-dimensional consolidation of double-layered soil with non-Darcian flow described by exponent and threshold gradient

Based on non-Darcian flow law described by exponent and threshold gradient within a double-layered soil, the classic theory of one-dimensional consolidation of double-layered soil was modified to consider the change of vertical total stress with depth and time together. Because of the complexity of governing equations, the numerical solutions were obtained in detail by finite difference method. Then, the numerical solutions were compared with the analytical solutions in condition that non-Darcian flow law was degenerated to Dary's law, and the comparison results show that numerical solutions are reliable. Finally, consolidation behavior of double-layered soil with different parameters was analyzed, and the results show that the consolidation rate of double-layered soil decreases with increasing the value of exponent and threshold of non-Darcian flow, and the exponent and threshold gradient of the first soil layer greatly influence the consolidation rate of double-layered soil. The larger the ratio of the equivalent water head of external load to the total thickness of double-layered soil, the larger the rate of the consolidation, and the similitude relationship in classical consolidation theory of double-layered soil is not satisfied. The other consolidation behavior of double-layered soil with non-Darcian flow is the same as that with Darcy's law.

Mechanical Properties of Asphalt Pavement Structure in Highway Tunnel

A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles.The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer,the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the as- phalt layer were calculated.The influencing factors such as double-wheel weight;asphalt layer thickness;base course stiffness modulus and thickness;and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.

Analysis of one-dimensional consolidation of soft soils with non-Darcian flow caused by non-Newtonian liquid

Based on non-Darcian flow caused by non-Newtonian liquid, the theory of one-dimensional (1D) consolidation was modified to consider variation in the total vertical stress with depth and time. The finite difference method (FDM) was adopted to obtain numerical solutions for excess pore water pressure and average degree of consolidation. When non-Darcian flow is degenerated into Darcian flow, a comparison between numerical solutions and analytical solutions was made to verify reliability of finite difference solutions. Finally, taking into account the ramp time-dependent loading, consolidation behaviors with non-Darcian flow under various parameters were analyzed. Thus, a comprehensive analysis of 1D consolidation combined with non-Darcian flow caused by non-Newtonian liquid was conducted in this paper.

Stress states of thawed soil subgrade

The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.

Hydraulic Fracturing Stress Measurements and Their Implication for the Design of the First Concrete Lined Pressure Shaft in Sri Lanka

The Urea Oya Multipurpose Development Project （UMDP） is a water transfer, hydropower and irrigation in the south-eastern part of the central highland region of Sri Lanka. During geotechnical site investigation program 42 hydraulic fracture tests and 42 impression packer tests were carried out in 3 boreholes to about 840 m depth. Based on the stress measurements the minimum and maximum horizontal stress ratios were calculated. In situ stress computations at all the tests were based on the assumption that the principal stress components were vertical （σv） and horizontal （σH and σh, the maximum and minimum, respectively）. The results of the measurements had a direct impact on the design of the major openings bearing a high overburden--the underground powerhouse and the transformer cavern--and revealed a significant optimization potential concerning the selection of the lining system of the pressure shaft.

Analysis of 1D consolidation with non-Darcian flow described by exponent and threshold gradient

Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on the non-Darcian flow described by exponent and threshold gradient, the theory of 1D consolidation is modified in this paper to consider a linear variation in the vertical total stress with depth and the effect of ramp loading. The numerical solutions were derived in detail by the finite difference method for excess pore water pressure and the average degree of consolidation. Finally, the influence of various parameters on consolidation behavior was investigated. The results show that the rate of consolidation is reduced when non-Darcian flow described by exponent and threshold gradient is adopted in the theory of 1D consolidation. As well the distribution of vertical total stress has a great influence on the dissipation of excess pore water pressure, either for pervious top and pervious bottom (PTPB) or for pervious top and impervious bottom (PTIB). For the case of PTIB, the distribution of vertical total stress in a foundation has a great influence on the rate of consolidation; however, for the case of PTPB, the rate of consolidation is independent of the distribution of vertical total stress. The rate of consolidation is dependent on the ratio of the thickness of a soil layer to the equivalent head of the final average vertical total stress; the greater the value of this ratio, the slower the rate of consolidation. Finally, an increase in construction time reduces the consolidation rate of a foundation. Thus, consolidation behavior of 1D consolidation with non-Darcian flow has been thoroughly acquainted in this paper.