International Journal of Geomechanics

Fastest curve-fitting procedures are proposed for vertical and radial consolidations for rapid loading methods. In vertical consolidation, the next load increment can be applied at 50–60% consolidation (or even earlier if the compression index is known). In radial consolidation, the next load increment can be applied at just 10–15% consolidation. The effects of secondary consolidation on the coefficient of consolidation and ultimate settlement are minimized in both cases. A quick procedure is proposed in vertical consolidation that determines how far $c_v$ is calculated from the true $c_v$, where $c_v$ is coefficient of consolidation. In radial consolidation no such procedure is required because at 10–15% the consolidation effects of secondary consolidation are already less in most inorganic soils. The proposed rapid loading methods can be used when the settlement or time of load increment is not known. The characteristic features of vertical, radial, three-dimensional, and secondary consolidations are given in terms of the rate of settlement. A relationship is proposed between the coefficient of the vertical consolidation, load increment ratio, and compression index.

A set of analytical formulas for the estimation of foundation model parameters is presented by synthesizing mechanical models at three different levels with corresponding variants of a generalized continuum model presented recently. The generalized continuum model was derived using a unified approach on the basis of a subgrade idealized as an elastic layer of finite thickness overlying a rigid base without making prior simplifying assumptions. The spring stiffness in all variants is inversely proportional to the layer thickness, rendering the model sensitive to this parameter with the potential to yield excessively large deflections for thick formations. This problem is alleviated by eliminating the layer thickness through introduction of a calibration factor in the form of a ratio of the layer thickness to the foundation width. It has been demonstrated that the calibration factor for each model type can be established from comparative analytical-numerical studies. Values obtained in this manner are suggested for practical use. The proposed calibrated formulas have potential applications in routine analysis of beam-like and plate-like shallow foundations and rigid pavements.

This study explores the utility of a pressure-dependent empirical hardening parameter in estimating deformation of rock masses. The hardening parameter has drawn poor attention in classical rock mechanics. Review of previous literature and observation of test results show that hardening is highly dependent on confining pressures and the plasticity already experienced, which modify joint parameters by mutual interaction. This paper provides an insight into the published test data that reflects the dependencies of the in situ deformation modulus on incremental joint parameters and the isotropic pressure ratio. There exists an empirical relation between modulus ratio and modified joint factor derived from number of joints, roughness, joint inclination, and gouge parameters. The author has interpreted the modulus ratio of jointed rock based on the modified joint factor. The author applied a hardening parameter obtained from the initial condition of stresses and that of the joint on the modified joint factor to get a modulus ratio. Using a correlation of the modified joint factor and the rock quality designation (RQD), the model successfully shows that operating hardening parameter on RQD envelops the published data of modulus ratio versus RQD. The main aim of this paper is to show that the present model is valid for in situ deformation of the strain-hardening rock mass in structural foundation, mines, and excavation design.

Previous work indicated that rates of change of shear stress, effective normal stress, and void ratio of a sheared soil are proportional to applied values of shear and effective normal stress; initial proportionality values decay exponentially with strain to become zero at the steady-state condition. This paper proposes that the physical basis for this behavior is an underlying stochastic process in which particles move at random shear strains into the steady-state flow structure under the action of shear stress, countered by frictional resistance generated by the effective normal stress. The resulting dynamical systems model with physical properties closely fits 130 undrained and drained triaxial and true-triaxial shear tests, exhibiting strain softening or strain hardening, using various stress paths, conducted on uncemented, resedimented clays at various overconsolidation ratios (OCRs) and uncemented sands and silts at various relative densities. Parameters varied orderly with OCRs (clays) and confining pressure (silts and sands). The model’s value is that based on a simple hypothesis of particles moving into the steady state at random shear strains, it closely matches data from a variety of tests. Present limitations of the model are that it only applies to static loading and not yet to generalized stress paths found in field situations.

Statistical models have been developed to correlate resilient modulus with routine properties of subgrade soils and state of stress for pavement design application. An information theory approach is taken as a method in ranking models. This approach is compared with the $R^2$ approach. A short overview of the information theory approach is introduced without the mathematical proof of the formulas. The notion of ranking stability is introduced and supports the use of the information theory approach. Results are presented comparing the information theory approach and the $R^2$ method for two different data sets.

This paper investigates the effect of a preexisting natural fracture on hydraulic fracture propagation. A fully coupled numerical poroelastic model, which includes the wellbore, the formation, a hydraulic fracture, and an arbitrarily oriented natural fracture, has been developed and used for this purpose. The possibility of fracture diversion, intersection, opening, and breakout for different angles of approach as well as natural fracture length are investigated. The fully coupled poroelastic model and the improved knowledge derived from this study have beneficial applications in the design and optimization of hydraulic fracture treatments in naturally fractured reservoirs, including tight gas, coal bed methane, and enhanced geothermal reservoirs. Results of this study have shown that the orientation of the natural fracture (penny-shaped, mineralized and/or closed natural fracture is used in this study) and fracture length can severely influence the propagation trajectory of a hydraulically induced fracture. An induced fracture is more likely to cross a natural fracture with a length equal to or less than 10 m if the angle of approach is sufficiently high; otherwise, it intersects and dilates the natural fracture (fracture arrest) and breaks out from one of the tips of the natural fracture. It is also shown that natural fracture length equal to or greater than 20 m is likely to arrest a hydraulically induced fracture.

Propagation of a Love wave in an initially stressed fluid-saturated anisotropic porous layer with an irregular boundary sandwiched between two isotropic half-spaces has been studied. The irregularity is assumed to be rectangular, and the perturbation method is used to obtain the displacement field in the porous layer. Finally, the dispersion relation for the assumed model is obtained, and the result is compared with those derived for the flat layer theory. The effect of porosity, initial stress, and irregularity of the porous layer in phase velocity is studied and shown graphically.

The seismic excitation experienced by structures is a function of the earthquake source, travel path effects, local site effects, and soil-structure interaction (SSI) influences. The result of the first three of these factors is referred to as free-field ground motion. The structural response to free-field motion is influenced by the SSI. In particular, accelerations within structures are affected by the flexibility of the foundation support and variations between the foundation and free-field motions. Consequently, an accurate assessment of inertial forces and displacements in structures can require a rational treatment of SSI effects. In the current study, to depict these effects on the seismic response of moment-resisting building frames, a 10-story moment-resisting building frame resting on a shallow foundation was selected in conjunction with three soil types with shear-wave velocities of less than 600 m/s, representing Soil Classes Ce, De, and Ee according to an existing Australian Standard. The structural sections were designed after applying dynamic nonlinear time-history analysis, based on both the elastic method, and inelastic procedure using the elastic-perfectly plastic behavior of the structural elements. The frame sections were modeled and analyzed using the finite-difference method andthe FLAC 2D software under two different boundary conditions: (1) fixed-base (no SSI) and (2) considering the SSI. Fully nonlinear dynamic analysis under the influence of various earthquake records was conducted and the results of the two different cases for elastic and inelastic behavior of the structural model were extracted, compared, and discussed. The results indicate that the performance level of the model resting on Soil Class Ce does not change substantially and remains in the life safe level while the performance level of the model resting on Soil Classes De and Ee substantially increase from the life safe level to near collapse for both elastic and inelastic cases. Thus, considering SSI effects in the elastic and inelastic seismic design of concrete moment-resisting building frames resting on Soil Classes De and Ee is essential. Generally, by decreasing the dynamic properties of the subsoil such as the shear-wave velocity and shear modulus, the base shear ratios decrease while interstory drifts of the moment-resisting building frames increase relatively. In brief, the conventional elastic and inelastic design procedure excluding the SSI is not adequate to guarantee structural safety for moment-resisting building frames resting on Soil Classes De and Ee.

A detailed study on the postliquefaction undrained shear behavior of sand-silt mixtures at constant void ratios is presented in this article. The influence of different parameters such as density, amplitude of cyclic shear stress, and drainage conditions on the postliquefaction undrained response of sand-silt mixtures has been investigated, in addition to the effect of fines content. The results showed that the limiting silt content plays a vital role in the strength of the soil under both cyclic and monotonic shear loading. Both the liquefaction resistance and postliquefaction shear strength of the soils are found to decrease with an increase in the fines content until the limiting silt content is reached. However, further increase in the silt content beyond the limiting silt content increases the liquefaction resistance as well as the postliquefaction shear strength of the soils. It is also observed that these variations on the liquefaction and postliquefaction resistance of soils are closely related to the variations in relative density.

A three-dimensional (3D) FEM for examining the soil-building interaction based on an input seismic wave field is proposed. A seismic wave field means seismic waves propagating in a 3D medium. An input seismic wave field is employed with the goal of adequately treating seismic surface waves trapped by a deep (several kilometers) underground structure in a soil-building interaction system. As the first stage of the proposed method, a simple linear method is constructed. The linear method was applied to estimate seismic responses of low- to high-rise RC model buildings during a large earthquake at a soft-soil site in Mexico City where surface waves are dominant. At the soft-soil site, all the buildings with and without piles vibrated together with the ground, probably suppressing the pile damage. The proposed method qualitatively provided us with more realistic building responses, compared with a conventional interaction analysis based on an input base motion. When a considerable amount of surface waves are present at a soft-soil site, the proposed method needs to be employed.

A series of stress-controlled and undrained cyclic triaxial tests were conducted on mine tailings to investigate their dynamic properties and the influence of clay mineral types on their cyclic strength. The tests were performed on specimens with a cyclic shear stress ratio ranging from 0.10 to 0.40 under the same confining pressure. It was observed that the axial strain, excess pore water pressure, and damping ratio increase with the number of loading cycles, whereas the effective stress and dynamic shear modulus decrease with increasing number of loading cycles. The effect of void ratio on shear modulus was significant in the small strain range, and thereafter, the effect was not significant among the tailings studied. It was also observed that the cyclic strength of the tailings varies with the type of dominant clay mineral present in them. Tailings containing montmorillonite showed higher resistance to cyclic loading than those containing kaolinite.

Analysis of pile foundations for earthquake loads requires the consideration of inertial loads that result from the soil-pile-superstructure interaction, as well as the evaluation of kinematic interactions that result from the movement of the surrounding soil and the pile. Such soil-pile interaction analyses must consider the stiffness degradation that results from earthquake loading. In the current study, the soil-pile interaction analysis considers stiffness degradation effects for a range of earthquakes with different amplitudes [maximum horizontal acceleration (MHA)], mean time periods, and different durations of earthquakes. Effects of both kinematic and inertial interactions are evaluated using a seismic-deformation method. A computer program was developed using MATLAB for the analysis. Results of a ground-response analysis obtained from a separate study were used for the soil-pile interaction analysis. Pile response for kinematic interactions were validated with the available theoretical solutions in the literature. In addition, kinematic pile response was compared with field observations for an actual earthquake, and the results are presented. Parametric studies were carried out to understand the effect of the presence of a liquefying soil layer, depth of the liquefying layer, etc., and the results are presented. The results indicate that the effect of the depth of the liquefying layer has a significant influence on the pile-bending response and that the peak bending moment occurs at the interface of the liquefying and nonliquefying layers.

Data imbalance causes learning bias in class identification techniques. A major cause for limited success in the prediction of liquefaction potential by various pattern recognition techniques is because of a liquefaction to nonliquefaction data class imbalance. It is suggested to use a support vector data description (SVDD) strategy to compensate the minority data. SVDD is used to generate virtual data points for the minority class bearing the same characteristics as the nonvirtual samples. Then an adaptive neuro-fuzzy inference system (ANFIS) classifier is employed to determine the liquefaction threshold. The ANFIS predictions are then examined by evaluating the coefficient of determination (COD) and comparing it with the Bayesian updating method. It is shown that for the liquefied data the approach is as efficient as the Bayesian method, but great improvement in the recognition rates of the nonliquefied data have been achieved.

In this paper, the stress–strain state and the effectiveness of shear resistance of a glass fiber-reinforced polymer (GFRP) bar soil nail in a pullout test was studied in laboratory using fiber Bragg grating (FBG) sensing measurement. Both experimental study and numerical simulation were carried out and results are compared in this paper. In the pullout test, cement slurry was grouted into one predrilled borehole with a GFRP bar in a completely decomposed granite (CDG) soil mass, forming a cement-grouted GFRP bar soil nail. This GFRP bar soil nail was pulled out from the CDG soil mass in laboratory to investigate the performance of the GFRP bar soil nail during the pullout test process. Three loading cycles were applied to pull the GFRP bar soil nail out. Compared with traditional electricity-based strain gauges, FBG sensing technique is a relative novel technology to geotechnical structures health monitoring and has a number of advantages including high accuracy, multiplexing, electromagnetic interference resistance, and good repeatability. In the current study, one fiber line had a series of FBG strain sensors with a sequence of initial wavelengths. This fiber line with five FBG strain sensors was adhered on the pregrooved GFRP bar before grouting and was used to measure the strain distribution along this GFRP bar with cement grout during a pullout test. The mechanical behavior of the GFRP bar soil nail is evaluated by using the measured strain results in the paper. It is found that the pullout results of the GFRP bar soil nail are in good agreement with numerical calculation results. Test results also show that the FBG sensors are reliable for measuring the strain variation at all measured points under different loading stages. Furthermore, a simplified pullout resistance model originally proposed for GFRP pipe soil nails was employed to examine the laboratory pullout results of a GFRP bar soil nail. It is found that the simplified pullout resistance model is also applicable for the GFRP bar soil nail.

The light weight deflectometer (LWD) is a portable, nondestructive testing device that can estimate pavement layer parameters, namely moduli. Conventional backcalculation of layer parameters from LWD deflections is formulated as an inverse problem where predicted vertical deflections are matched to observed vertical deflections using a gradient search algorithm. In this paper, we present an LWD backcalculation scheme to recover layer parameters, including top-layer thickness, of a two-layer earthwork system. Our approach resolves the problem using a dynamic finite-element (FE) model for the forward calculation of LWD deflection data and implements a genetic algorithm (GA) as the inverse solver. The objective function we minimize is formulated as a measure of the data misfit between predicted and observed data, normalized by the peak deflections, and it includes 180 data points from the dynamic deflection time history. The objective function contains multiple local minima that can potentially trap gradient search algorithms, thus validating application of GA as a global search technique for this problem. The GA is applied to both synthetic and experimental data, and we demonstrate that the recovered top-layer thickness, top-layer modulus, and underlying modulus for the experimental data compare favorably with expected values.

This paper presents the load-settlement response of a surface footing placed over buried flexible pipe through model plate load tests. Experiments are conducted in a rectangular box after placing a model footing on the surface of sand placed at two different relative densities. Combination of tests were performed, such as, (1) model footing placed over sand compacted at low relative density ($\text{RD}=50\%$) and model buried flexible pipe (PVC pipe) placed at 0.5 B and 1.0 B depth, and (2) model footing placed over sand compacted at high relative density ($\text{RD}=88\%$) and model buried flexible pipe (PVC pipe) placed at 0.5 B & 1.0 B depth; where B = diameter of the model footing. The results of the model plate load test provide useful interpretation about the combined behavior of buried flexible pipe–soil system in terms of load-settlement response. The influence on the bearing capacity of sand in different relative densities and that caused by the presence of a buried flexible pipe beneath the footing is also discussed. Experimental results are also verified numerically using the two-dimensional finite-element tool PLAXIS, and results are discussed in light of the experimental findings. Furthermore, a soil nailing technique is also explored experimentally and numerically to establish its usefulness in terms of improving the bearing capacity of the buried flexible pipe soil system in a given sand medium.