International Journal of Geomechanics

This paper presents modification of the derivation of a previously proposed constitutive model for the prediction of stress-strain behavior of municipal solid waste (MSW) incorporating different mechanisms, such as immediate compression under loading, mechanical creep, and time-dependent biodegradation effect. The model is based on critical state soil mechanics incorporating increments in volumetric strains because of elastic, plastic, creep, and biodegradation effects. The improvement introduced in this paper is the modified critical state surface and considers five variable parameters for the estimation of stress-strain behavior of MSW under different loading conditions. In addition, an expression for the strain hardening rule is derived, with considerations of time-dependent mechanical creep and biodegradation effects. The model is validated using results from experimental studies and data from published literature. The results are also compared with the predictions of the stress-strain response obtained from a well-established hyperbolic model.

This paper introduces an equivalent stress for elastoplastic modeling of unsaturated soils. This equivalent stress unifies various models for unsaturated soils with regard to the stress variables used and allows for a simple separation of the saturated and unsaturated phases of behavior. Moreover, the equivalent stress computed for a given model for unsaturated soil can be used in an existing model for saturated soil so it will gain the ability to model the former. The unsaturated plastic volumetric behavior of the new model is inherited mostly from the parent model for unsaturated soil. The behavior upon shearing depends on both models: the shape of the yield locus is inherited from the original model and the increase of the elastic zone (and possible shift of the elastic zone) from unsaturation depends on the model for the unsaturated soil from which the equivalent stress was taken.

In this work, a series of fully coupled three-dimensional thermomechanical finite-element analyses has been carried out to investigate the mechanical and thermal interaction effects induced in a small piled raft equipped with energy piles during the operation of an air-conditioning system based on ground source heat pumps (GSHPs). In particular, attention has focused on (1) the axial-load redistribution among the various piles of the raft as a result of differential thermal dilations occurring in the pile and the soil during the transient heat conduction process and (2) the thermal interaction effects that may affect the heat exchange process when multiple energy piles are placed at short distances within the same piled raft. The results of the numerical simulations, which are in qualitative agreement with the limited experimental observations from full-scale tests on energy piles currently available in the literature, show that significant (positive and negative) axial-load changes can be experienced by both thermally active and nonactive piles of the raft. The load redistribution effects among the piles of the raft reach their peak at a very early stage of the thermal conduction process, when the differences in temperature among active and nonactive piles are largest, and then reduce steadily with time up to steady-state conditions. For the thermal properties of the soils and the raft geometries considered in this study, the peaks in axial-load variations are observed within about 30 days after the beginning of the thermal stage. This time span is well inside the normal operation times of GSHP systems, of the order of a few months. As for the thermal efficiency of the system, the numerical results show that in the same time span the thermal interaction effects between the various heat exchangers in the raft are negligible; however, significant reduction in the specific heat flux to and from the soil can be observed for larger operation times.

Installation of stone column is a viable, cost effective, and environmentally friendly ground-improvement technique. Columns are made of compacted aggregate and are installed in weak soil as reinforcements to increase the shear resistance of the soil mass and, accordingly, its bearing capacity. While a single stone column mostly fails by bulging, a group of stone columns together with the surrounding soil may fail by general, local, or punching shear mechanism, depending on the soil/columns/geometry of the system. The mode of failure of the reinforced ground could be identified based on the ground geometry and strength parameters of both stone column and soft soil. This paper presents an analytical model to predict the bearing capacity of soft soil reinforced with stone columns under rigid raft foundation subject to general shear-failure mechanism. The model utilizes limit-equilibrium method and the concept of composite properties of reinforced soil. The proposed theory was validated for the case of bearing capacity of footings on homogenous soil and via the laboratory and numerical results available in the literature for this case. Design procedure and charts are presented for practicing purposes.

The performance evaluation of buried extensible plastic pipelines, such as polyethylene pipes in the gas distribution industry, in areas prone to ground movement is a key consideration for many utility owners. Considering the relatively smaller deformation stiffness and nonlinear stress-strain response of these pipes compared with those of steel pipes, a good understanding of the basic soil–pipe interaction mechanisms forms a critical part in these evaluations. The increase in soil normal stress on the pipe attributable to soil dilation and gradual degradation of interface friction with axial pipe displacement was investigated. An analytical method was developed to estimate the pipe response when subject to axial frictional loads arising from soil movements, which accounts for these factors and the nonlinear stress-strain response of the pipe material. For a known relative axial soil displacement, the approach provides a convenient way to determine the axial force, strain, and length along which the friction is mobilized. The proposed analytical solution was used to model the response of five large-scale field pipe pullout tests. It is shown that the analytical solution is capable of effectively forming a framework to relate pipe displacement, pullout resistance, strain, and mobilized length. The findings also highlight the significance and need to account for soil dilation effects in describing the soil–pipe interaction in extensible plastic pipes.

The oedometers used for one-dimensional consolidation tests are proportioned such that their height-to-diameter ratio lies in the range 0.17–0.40. Sometimes, it is desirable to test a soil specimen that has a significantly larger height-to-diameter ratio, where the wall friction must be considered in the analysis. Such tall oedometers can become useful tools in consolidation tests, if the wall friction can be accounted for rationally. The objective of this paper is to develop some theoretical basis for analyzing consolidation test data from tests carried out in tall oedometers. It is shown that the same average degree of consolidation versus time factor charts can be used for height-to-diameter ratios as much as 3, provided the specimen is doubly drained. Consolidation tests carried out in the standard oedometer and tall oedometer in the laboratory gave very similar values of coefficients of consolidation.

The present research intends to study the effects of the seismic soil-pile-structure interaction (SSPSI) on the dynamic response of buildings with various heights by conducting a series of shaking table tests on 5-, 10-story, and 15-story model structures. Two types of foundations for each case are investigated, including (1) a fixed-base structure, representing the situation excluding the soil-structure interaction; and (2) a structure supported by an end-bearing pile foundation in soft soil. An advanced laminar soil container has been designed that uses three-dimensional numerical modeling to minimize the boundary effects and to simulate free-field motion during the shaking table tests. Four real earthquake events, including Kobe 1995, Northridge 1994, El Centro 1940, and Hachinohe 1968, are imposed to each model. According to the experimental measurements, it is observed that the SSPSI amplifies the maximum lateral deflections and in turn interstory drifts of the structures supported by end-bearing pile foundations in comparison with the fixed-base structures. The rocking component plays an important role in increasing the lateral deflection of the superstructures, which can shift the performance level of the structures to near collapse or even collapse levels and as a result should be assessed precisely in the seismic design of buildings resting on soft soils.

Geotextile-reinforced embankments over deep cement mixed (DCM) columns are widely used for the construction of highway embankments over soft clay with low shear strength and high compressibility. Numerical modeling based on the FEM is widely used to investigate the behavior of these embankments during construction and serviceability, incorporating consolidation of the foundation soil over time. However, not much attention has been paid to the strain-softening behavior of DCM columns beyond yield, which is essential in ultimate limit-state computations to determine the stability of embankments during the failure of columns. This paper presents a constitutive model, which is an extension of the Mohr-Coulomb model, for the simulations of strain-softening behavior of cement admixed clays. The model is validated using triaxial test data found in the literature for cement admixed Singapore and Hong Kong marine clays and Ariake clay. A two-dimensional (2D) coupled mechanical and hydraulic numerical implementation of a geotextile-reinforced DCM column-supported (GRCS) embankment constructed over a very soft soil in Finland is carried out incorporating strain-softening behavior of DCM columns. Even though the isolated columns and overlapped column walls used in this embankment do not yield significantly under the service loads, the model simulations show good agreement with field data, confirming the capability of the 2D plane strain finite-element model in predicting the GRCS embankment behavior. Finally, the finite-element model with strain-softening DCM columns is used to investigate the progressive failure of a typical hypothetical GRCS embankment with isolated columns in a square pattern. Results clearly illustrate the bending failure mode caused by progressive softening of the DCM columns, including the plastic hinge development within the columns.

This paper studies the propagation of horizontally polarized shear waves (SH-waves) in a heterogeneous fiber-reinforced medium over a heterogeneous half-space under gravity. The inhomogeneity of the layer and half-space is caused by the exponential variations of elastic parameters. Dispersion relation is obtained in a closed form, which is in agreement with the classical Love wave equation. The effect of heterogeneity, reinforcement, and gravity is studied and is represented by a graph. It is observed that inhomogeneity, reinforcement, and gravity have a significant effect on the velocity profile of SH-waves.

The growth of precision autoguidance systems on construction equipment suggests that nonplanar slopes and landforms now can be constructed readily. Slopes with concave cross sections not only appear more like natural slopes, but can also have superior stability and erosion resistance. Thus, it is desirable to have the description of concave slopes that provide mechanical stability for a given set of soil properties. In this paper, an approximate solution that defines the geometry of critical concave slopes (factor of safety $\text{≈}1$) in a frictional medium is developed, based on the slip-line field method. The approximate solution is compared with previous numerical results and validated via limit-equilibrium method and FEM analyses. The proposed solution is simple in form, and, when implemented with precision construction equipment, will allow the construction of embankments and reclaimed mine lands that appear more like those in nature and yet are more resistant to erosion.

Piles have been widely used to resist lateral loads in geotechnical engineering. In reality, piles are always embedded in layered soils; however, theoretical solutions for laterally loaded piles in multilayered soil system are limited in the literature. Based on the basic concept of the subgrade reaction theory, semianalytical solutions using the power series method were proposed to assess the behavior of a vertical pile with variable cross sections and embedded in a multilayered soil system to support lateral loads at its head. For the present method, the moduli of the lateral subgrade reaction were assumed to be of constant depth for clay soil and of linearly increasing depth for sandy soil. By considering the deflection and force continuum conditions along the pile length, a matrix form of pile response at any depth was expressed through the deflections and lateral forces at the pile head. The validity of the presented solution was verified by back-predicting behaviors of laterally loaded piles in two existing cases. Moreover, four hypothetical cases related to laterally loaded piles in uniform and layered soil systems were set up to discuss the response of the laterally loaded pile in layered soils. The comparison results indicate that the pile behavior is controlled by the subgrade soil stiffness at shallow depth (up to 3–4 times the pile diameter). It also indicates that the interlayer with a higher stiffness embedded near the ground surface, such as a sand layer presented within clay deposit, has a reduction effect on the maximum pile lateral deflection, but has a slight effect on the maximum bending moment of the pile.

The role of statistical tools in the modeling of slope stability has been increasingly studied in the last decades. Mainly, this growth can be related to the availability of fast computational routines that enable massive-repetition numerical algorithms such as Monte Carlo simulations. On the other hand, analytical approaches to this problem, in the majority of cases, rely on considering the random variables of interest being normally distributed. This latter assumption tends to provide incorrect results when dealing with skewed data because normal distribution is symmetric about its mean value. To address this issue, a complete statistical study of a set of porosities data is undertaken. A total of seven well-known statistical distributions are adjusted to such data, showing that normal distribution is the worst possible fit for the considered data set. By means of an empirical correlation between strength properties and porosity, the probability-density function of the factor of safety of a hypothetical slope is analytically derived based on a Mohr-Coulomb failure criterion. This way, it is shown that the probability of failure can be explicitly obtained by means of solely the distribution of a primary property of the material in study, namely, its porosity. Also, the results obtained by considering the porosity data normally distributed are compared with the ones hereby developed, showing considerable differences.

Scouring is a significant problem on river bank and coastal protection systems. Severe scouring can cause damaging consequences to geotextile tube embankment structures. In this study, five case scenarios of an embankment system supported by stacked geotextile tubes were analyzed using a commercially available finite-element analysis software. These case scenarios include (1) conventional geotextile tube stacking on ground base foundation; (2) geotextile tube stacking on gravel bedding foundation; (3) geotextile tube stacking on excavated foundation; (4) geotextile tube stacking on excavated foundation with gravel bedding; and (5) fortification of stacked geotextile tubes by riprap protection. Each case scenario is simulated under normal loading and critical loading conditions with and without scouring at the base toe of the embankment system. Results suggest that the potential problems that occur during scouring and critical states of the embankment system instigate failures that could destabilize the geotextile tube retaining structure. Among all the case scenarios considered, additional fortification by riprap increases the performance and global stability of the geotextile tube embankment system.