Saturated Ground Research Articles

Numerical tests on dynamic response of pile-supported reclaimed embankment for high-speed railway in saturated soft ground using soil–water coupling elastoplastic FEM

High-speed train (HST) running in the saturated soft ground induces significant vibration that may threaten the running safety and serviceability of high-speed railway (HSR). Extensive studies have been conducted on the dynamic responses of HSR, yet, the soil–water coupling and plastic behavior in the saturated soft ground are rarely considered, and thus the build-up of excess pore water pressure (EPWP) and displacement cannot be accurately calculated. In this study, 2D soil–water coupling elastoplastic FEM was employed to investigate HST induced vibration in the pile-supported embankment using FE code called DBLEAVES. Dynamic soil stress, EPWP, acceleration and displacement under different cases were numerically analyzed in detail. Numerical tests confirm that liquid phase in soft ground plays important influence on the dynamic responses that vertical acceleration and displacement will be overestimated while the horizontal acceleration and displacement as well as EPWP will be underestimated if soil–water coupling is not considered. Single-phase analysis also exaggerates the acceleration attenuation and underestimate the vibration amplification in soft ground. The existence of piles can induce significant soil arching effect in the embankment, the distributions of vertical acceleration and EPWP are partitioned sharply by the piles while vertical displacement in soft ground becomes more uniform along the depth direction within the pile reinforced area. The existence of piles also induces stronger vibration beneath the pile end so that larger EPWP is generated below the pile end than around the pile body. The main influence area due to HST vibration for pile-supported embankment is overall 20 m away from the centerline of HSR track, therefore, it is reasonable to improve the ground by properly increasing the number of pile within this area. When the number of pile is determined, increasing the length of pile or reducing the pile spacing are two effective ways to mitigate the dynamic response.

Bearing characteristics of a model piled raft foundation in unsaturated soil subjected to variations in the groundwater level

The bearing characteristics of a piled raft foundation (PRF) in saturated or dry soil ground have been investigated in previous studies. However, soils near the ground surface are generally in an unsaturated state. Matric suction occurs in unsaturated soils and influences the mechanical properties of soil. For more reasonable designs of PRFs, it is undoubtedly necessary to study the bearing characteristics of PRFs in unsaturated soil. In this study, model tests were conducted to investigate the bearing characteristics of a PRF in unsaturated soil subjected to variations in the groundwater level. The experimental results showed that, when the groundwater level was increased and the suction decreased, the load carried by the raft increased under dead load, leading to a significant settlement of the model PRF.

A coupled MPM-FDM for seepage failure analysis of saturated ground

A coupled MPM-FDM for seepage failure analysis of saturated ground

Rheological consolidation analysis of saturated clay ground under cyclic loading based on the fractional order Kelvin model

AbstractBased on Biot porous medium theory, considering the coupled reaction of soil skeleton rheology and pore pressure dissipation, the present work investigates the dynamic consolidation characteristics of saturated clay ground under cyclic loading. First, the rheological behavior of the soil skeleton was described by the fractional order Kelvin model. The dynamic consolidation governing equations for the saturated clay were established theoretically in a three‐dimensional axisymmetric coordinate system. Second, the transform domain analytical solution of the dynamic consolidation of saturated clay was obtained using the Hankel–Laplace coupled transform method, and the solution in the time–space domain was further obtained through numerical inversion. Finally, the rheological consolidation behavior of saturated clay under cyclic loading and the influences of parameters were analyzed. The results show that the rheology of the soil skeleton had an inhibitory effect on pore water permeability; compared with elastic skeleton soil, the rheological clay had a slower settlement rate in the primary consolidation stage, a faster rate in the secondary consolidation stage, and greater long‐term settlement. In addition, under cyclic loading, the pore pressure response in saturated clay lags behind the effective stress, and a larger viscous order is associated with faster development of cumulative settlement.

Dynamic shakedown behaviors of flexible pavement overlying saturated ground under moving traffic load considering effect of pavement roughness

This paper presents a novel semi-analytical framework to dynamic shakedown behaviors of flexible pavement overlying saturated layered ground under moving traffic load. Distinctively, the framework accounts for the influence of dynamic component of vehicle load caused by pavement roughness on the dynamic responses and the shakedown limit analysis. By applying the Fourier transform technique and the robust global matrix method (GMM), the problem considered is formulated as a comprehensive matrix equation. This matrix equation integrates the boundary conditions, the continuity conditions at the interfaces, and the general solution to a single-layered saturated porous medium. By converting the solution to the real-time domain via the composite Gauss-Legendre integral method, the dynamic shakedown limit of pavement overlying layered half-space ground is determined using Melan’s lower-bound shakedown theorem. After verifying the present solution with two well-established solutions using other solution techniques, parametric analyses are performed to explore the dynamic responses of the layered ground at varying traffic load speeds. Special attention is paid to the effects the subsoil stiffness, traffic load moving speed, pavement friction coefficient, and pavement roughness on the dynamic shakedown limit. This newly proposed framework holds promise for designing layered road structures, factoring in dynamic responses and dynamic shakedown limits.

Experimental investigations on reliquefication resistance of saturated ground reinforced with ordinary and encased stone columns

Experimental investigations on reliquefication resistance of saturated ground reinforced with ordinary and encased stone columns

Stability of tunnel face in unsaturated sand possessing apparent cohesion: A micro-macro analytical approach

Although the stability of tunnel face in the dry and saturated sandy ground is widely studied, the unsaturated sandy ground which possesses apparent cohesion is more common in engineering. For remedying this deficiency, the theoretical association between apparent cohesion and the saturation degree is firstly established in microscopic prospective. Then, the formation mechanism of the self-stabilized arch and the limit support pressure (LSP) of the tunnel face are derived by incorporating apparent cohesion into the macroscopic limit equilibrium analysis of the multi-arches model. Subsequently, the validities of the proposed approach in estimating apparent cohesion, loosening zone height and LSP are well confirmed (the average error rates of LSP are within 12 %) via comparisons with direct shear tests, model tests and other existing methods. Finally, as revealed by the parametric discussion, under the effect of apparent cohesion, LSP is negatively correlated with compactness, internal friction angle, and contact angle while decreases firstly (to a minimum value of 0.09γD ∼ 0.15γD) and then increase with the rise of saturation degree. Besides, the LSP has a parabolic distribution along the depth with its peak value emerges between 0.3D and 0.45D.

Investigation on the Damping Effect of FST System under Moving Load Using the Track–Tunnel-Layered Saturated Ground Model

In this paper, a single-tier beam-spring-damping system and a two-tier beam-spring-damping system are adopted to simulate the FT (fixed track) and FST (floating slab track) system, respectively. The tunnel is modeled as an infinitely long Euler—Bernoulli beam embedded in the layered saturated soil. By solving the governing equations of the saturated soil and employing the TRM (transmission and reflection matrices) method, the frequency response function of the tunnel-layered saturated soil model is obtained. Making use of the interaction between the tunnel and track systems, the track system is coupled with the tunnel-layered saturated ground model. The solutions for the dynamic response of the track system–tunnel-layered saturated ground model under moving loads in the time–space domain are obtained using the inverse Fourier integral transform. To evaluate the damping effect of the FST system on the vibration of tunnel and soil, four damping coefficients are defined and the vibration results of the FT system–tunnel-layered saturated soil model are compared with those of the FST system–tunnel-layered saturated soil under different moving loads and soil conditions. The numerical results show that both the vibration displacement and acceleration amplitude are attenuated after using the FST system, and the damping coefficient of acceleration is about 30% greater than that of the displacement. In addition, the damping effect of the FST system on the ground surface vibration is associated with the embedded depth of the tunnel and the soil stiffness.

Experimental studies on liquefaction and reliquefaction potential of saturated ground subjected to repeated incremental acceleration loading with varying shaking duration

Experimental studies on liquefaction and reliquefaction potential of saturated ground subjected to repeated incremental acceleration loading with varying shaking duration

Dynamic shakedown limits of the pavement on saturated subgrade subjected to traffic rolling-sliding loading

This paper establishes a semi-analytical lower-bound dynamic shakedown method to investigate the shakedown of the pavement on saturated subgrade based on dynamic Biot's consolidation theory, considering a rolling-sliding contact between vehicle tire and pavement. This analysis has demonstrated that properties of the saturated subgrade generally have negative effects on the shakedown limit of the pavement system under high-speed traffic loadings. In general, the classical single-phased shakedown theorem overestimates the shakedown limit of the pavement on the soft ground of low permeability, particularly under high-speed traffic loadings. The shakedown limit of the pavement on a saturated subgrade gradually reduces with decreasing permeability of the subgrade. The sliding-induced friction significantly affects the shakedown limit and the location of critical shakedown failure. The permeability of the saturated subgrade has considerable effects on the shakedown limit for the case of low tire-pavement friction. The shakedown limit of the pavement on a saturated subgrade and a single-phased subgrade shows a considerable difference at the optimum modulus ratio, at which the critical shakedown failure tends to shift from the saturated subgrade to the pavement layer. The proposed method will be more desirable to evaluate the performance of the pavement in the saturated soft ground.

A DRM-SMM Framework for Wave Propagation in Layered Saturated Ground under Inclined P1-SV Waves

This paper provides a numerical framework for seismic analyses for layered saturated ground under inclined plane P1-SV waves. A unified stiffness matrix method (SMM) formula for both u-w-p and u-p formulations is first derived to obtain the dynamic response of saturated fields. Then, the domain reduction method (DRM) is extended to two-phase media to reproduce the target wavefield within the numerical models. The accuracy of the proposed SMM-DRM framework is verified by comparisons with analytical solutions and other numerical methods. Its applicability in complex boundary value problems is also proven by solving a typical SSI problem. The numerical framework is especially advantageous in the analyses of complex subdomains under obliquely incident seismic waves. With the procedure given in the paper, the framework can be implemented into existing finite element models straightforwardly.

ANALISIS DEFORMASI DAN STABILITAS LERENG DENGAN VARIASI GEOMETRI DAN PERKUATAN GEOTEKSTIL PADA PROYEK GEDUNG FAKULTAS HUKUM UII

Indonesian Islamic University (UII) is a private university located in Sleman, Special Region of Yogyakarta. As an educational institution, UII must be able to fulfill the infrastructure to carry out the teaching and learning process for its students, namely the lecture building. At present UII has campuses spread across Kaliurang (integrated campus), Condongcatur (Faculty of Economics), and student parks (Faculty of Law). The process of building a law faculty building UII is on the road Kaliurang km14.5 which is just below the foot of Mount Merapi and has contours of mountainous land. The contours of mountainous land have different levels of land up and down. In mountainous areas can cause problems, namely landslides. In the construction of the UII law faculties building, a suitable slope design is needed, so to solve the problem, slope stability analysis is used. This method is carried out by analyzing the deformation and slope stability by strengthening the geotextiles using the Plaxis 8.2 program. Slope modeling is designed with variations in geometry and variations in water level. Geometry variations used are geometry 70 °, 60 °, and 50 ° while variations in water level with dry water conditions, depth of water conditions 3.8 m, and saturated water conditions. In carrying out the analysis using structural loads and earthquake loads. Deformation analysis is seen from horizontal point X deformation, vertical point X deformation and horizontal deformation of Y-Y pieces. The results of this study are that slope with geotextile reinforcement have large safety factor and small deformations. A more slope geometry variation (50°) result in a larger safety factor and has a small deformation than steep geometry (70°). Groundwater variation have an influence on the results of the safety factor and deformation. The face of saturated ground water has a low safe value and large deformation due to having more water content.

Modelling of critical speed of railway tracks on a multi-layered transversely isotropic saturated ground

The responses of railway tracks are significantly amplified when the high-speed train travels around the speed of waves propagating in underlying soils. The dynamic amplification phenomenon corresponding to the issue of the critical speed may compromise the stability and safety of operation and increase track damage. This paper proposes an analytical model to analyze the effect of the transverse isotropy of ground on the critical speed of railway tracks on stratified saturated soils. By using the Biot's theory, the general solutions of the transversely isotropic saturated porous medium are derived by employing the potential decomposition and Fourier transform. The transmission and reflection matrix method is extended to derive the three-dimensional fundamental solution for moving point loads acting on a multi-layered transversely isotropic saturated half-space. The models for railway tracks and wheel-axle loads are subsequently coupled to the ground. The proposed model is validated through a comparison with two existing models. Numerical studies demonstrate that the material anisotropy changes the critical speed and the corresponding dynamic amplification coefficient by up to 20%. The anisotropy in the shear modulus has the most significant influence on the critical speed, followed by Young's modulus and the permeability coefficient. The material anisotropy and soil layering cannot be ignored for the assessment of the critical speed of a track-ground system.

Soil arching evolution caused by shield tunneling in deep saturated ground

Shield tunneling is accompanied by variations of stress and displacement in soil, which could induce the soil arching effect. Although there have been many studies on the soil arching effect caused by shield tunneling, the research on deep-buried and saturated conditions is still lacking. In this study, a finite element model was firstly built and verified by field data. Then, two hypothetical finite element models were established with two different strata to investigate the stress transfer mechanisms, the development law of excess pore water pressure, and the soil arching evolution of deep-buried tunnel. The methods to determine the arch zone and loosened zone were proposed and verified, which were adopted to compare the differences of soil arching effect between saturated sandy and clayey soil layers. The results show that the heights of the arch zone and loosened zone in the saturated sandy soil layer are both higher than those in the saturated clayey soil layer after the shield tunneling. The subsequent strata consolidation resulted in a 36% reduction in the arch zone height in clayey soil, which means that time effect for the soil arching is significant. Compared with Terzaghi's loosening earth pressure theory, in deep ground, the theoretical overburden pressure is only 5.0% larger than the numerical results for sandy soil but 18.3% less than that for clayey soil. The numerical results can bring new sights about the soil arching evolution caused by shield tunneling and the corresponding tunnel overburden pressure in deep saturated ground.

Optimization of construction parameters of large rectangular pipe jacking in saturated soft ground

Optimization of construction parameters of large rectangular pipe jacking in saturated soft ground

Shear and compression waves screening in 2D for dry or saturated ground using periodic infinite and finite soil-foam barriers

Shear and compression waves screening in 2D for dry or saturated ground using periodic infinite and finite soil-foam barriers

Simplified mathematical modeling to plane strain consolidation considering unsaturated and saturated conditions for ground with anisotropic permeability

Road embankment where the unsaturated soil layer lies above the saturated soil layer is often encountered in geotechnical engineering, but the analytical models for evaluating the plane stain consolidation characteristics of an unsaturated–saturated ground are limited. With a combination of the consolidation theories for saturated and unsaturated soils, this paper thus develops a plane strain consolidation model for exploring the transient behavior of unsaturated–saturated soils subjected to instantaneous loading. A semi-analytical solution, which is a simple tool for assessing unsaturated–saturated soil consolidation, is proposed by making use of decoupling strategy, Fourier expansion as well as Laplace transformation. Further, the proposed solution in this paper is validated by the published analytical or semi-analytical solutions in some specific cases. By implementing the proposed solution into a computation, the consolidation behavior of an unsaturated–saturated subgrade is presented, and the effects of important factors, including the anisotropic permeability ratio and interlayer permeability ratio, are studied. The anisotropic permeability ratio and interlayer permeability ratio are significant indexes to change the consolidation rate of lower soils so that the prefabrication of lateral drainage boundary on both sides of the unsaturated–saturated subgrade would accelerate its consolidation.

Theoretical investigation on characteristics of field reactions of saturated ground subjected to vibrations of inclined pile groups

Inclined pile groups have been adopted in engineering practice (e.g. offshore wind turbines) to withstand strong horizontal environmental loads that are repetitive in nature. Field reactions including the additional stresses and excess pore water pressures are responsible for the cyclic degradation of foundation soil, which may induce the accumulative deformation and fundamental frequency shifting of the marine structure. In this study, a theoretical model incorporating an inclined pile group and a saturated half-space was established, wherein the pile and saturated soil were described by the E–B beam and Biot poroelasticity theories, respectively. The pile and soil were coupled through the receptance matrix, which was established at the pile–soil interaction points in the transform domain. The dynamic impedances of the inclined pile group are first obtained, and then the field responses, including stresses and excess pore water pressure in the saturated ground, are evaluated for different types of loads applied to the pile cap. The frequency response function and spatial distributions of the field responses were obtained for varying rake angle of pile and permeability of soil. It was found that the horizontal force induces the largest responses in the ground when compared to the vertical force and the overturning moment applied to the inclined pile group. It is beneficial to employ an inclined pile group to withstand the horizontal force and overturning moment because the foundation stiffness increases, and the additional stresses in the ground decrease with increasing rake angle.

Analysis of face stability for tunnels under seepage flow in the saturated ground

Based on the three-dimensional hydraulic head distribution model and the upper bound theorem of the limit analysis, a new model was established to calculate the limit support pressure in shield tunnel faces. A series of numerical simulations were conducted to evaluate the accuracy of the proposed model and the obtained results were compared with those of other classical analytical methods. It is found that the obtained analytical solutions are in good agreement with the numerical simulations and the proposed method outperforms other methods in terms of accuracy. In the present study, the influence of the water level, internal friction angle, burial depth, and water pressure on the stability of the tunnel face is analyzed. The performed analyses reveal that the limit support pressure is negatively correlated with the internal friction angle, while the burial depth does not affect the limit support pressure of the shield tunnel face in subsea tunnels (C/D ≥ 1). Meanwhile, it is found that as the water level and the water pressure on the tunnel face increase, the limit support pressure increases linearly, and the failure area extends to the front of the tunnel face and decreases in height.

One-dimensional consolidation of unsaturated–saturated soil system considering pervious or impervious drainage condition induced by time-dependent loading

Since the ground with unsaturated soil layer and saturated soil layer is very common in most areas, a more comprehensive analytical solution is essential for the accurate prediction of ground consolidation behavior. In this paper, the one-dimensional consolidation theories for unsaturated and saturated soils are introduced to simulate the consolidation characteristics of the different soil layers, and the hypothetical soil interface of two layers that only allows pore water to flow is supposed in this model. After using the decoupling and Laplace transformation techniques to the coupled governing equations, the general Laplace-domain solutions are proposed under the permeable or impermeable surface for ground consolidation that an unsaturated–saturated ground with finite thickness subject to arbitrary time-dependent loading. The results in the temporal domain for the excess pore pressures and soil settlement are numerically obtained by Crump’s algorithm. The methodology and proposed solution are validated by some published solutions in the literature. Based on the proposed solutions under the three representative boundary conditions, the temporal behavior of ground subjected to ramp loading is explored. The results show that boundary condition would significantly affect the evolutions of excess pore pressures and further change the ground settlement.