Journal of Geotechnical and Geoenvironmental Engineering

Analytical solutions for axial displacement, strain, and stress in an end-bearing energy pile subjected to a thermal load and a combined thermal and mechanical load have been derived and validated against full-scale in situ pile tests. The pile is embedded into a single layered and multilayered soil underlain by stiff bedrock. The thermoelastic constitutive law has been used to describe pile behavior, while soil–pile interface has been characterized by a linear elastic load-transfer function. In the case of thermal load, the solutions for a single-layered soil show that both the absolute minimum magnitude of axial strain and the absolute maximum magnitude of axial stress develop at the pile tip. Thus, the maximum compressive and maximum tensile stress develops at the pile tip for net heating and cooling scenarios, respectively. When subjected to combined thermal and mechanical load, the shapes of the corresponding displacement and strain and stress response curves are dominated by either the response to thermal or the response to mechanical load, depending on the ratio of the magnitudes of the temperature change and the axial force applied at the pile head. The analytical solutions provide not only a quick quantitative assessment, but also an in-depth qualitative understanding of the thermomechanical soil structure interaction in energy piles.

Urban soft-ground tunneling projects involve significant risks related to the spatial variability and uncertainty in geotechnical parameters. However, standard practice typically does not incorporate spatial trends into risk assessment. Geostatistical methods provide a means not only for predicting geotechnical parameter values spatially, but also for modeling the heterogeneity and spatial uncertainty that play a key role in probabilistic risk assessment for tunnel construction. Before incorporating geostatistical analysis into the risk assessment for soft-ground tunneling works, it is necessary to identify best practices with respect to geostatistical methods. In this paper, two approaches were examined and compared for modeling the spatial variability and uncertainty of key geotechnical parameters relevant to shield tunneling in soils. The first approach consisted of the sequential Gaussian simulation of parameters using a single spatial variance model for each respective parameter, which is a common approach adopted in the literature but does not incorporate variability and uncertainty in geological units. The second approach considered the influence of geology by basing the sequential Gaussian simulation of geotechnical parameters on geological unit simulations using a transition probability-based stochastic model. In this approach, a unique spatial variance model of the geotechnical parameter for each geological unit was considered. The results from this analysis revealed that the influence of geology is critical to the spatial modeling of geotechnical parameters and their uncertainty, and, therefore, must be incorporated into the geostatistical analysis for the risk assessment of soft-ground tunneling works.

The dynamic behavior of a peat deposit in the north of the Netherlands is described. The organic content ranges from 70% to 95%, which is high compared to the organic content generally presented in publications on the dynamic behavior of peats. Shear wave velocities $v_s$ and correspondingly small-strain shear moduli $G_0$ closely match values stated in the literature. Correlations stated in the literature for predicting $G_0$ proved to be applicable. Resonant column and cyclic direct simple shear tests were performed to establish the shear modulus reduction curves and damping curves. Excess pore pressure development during testing indicates dilatant behavior. The general trend shows nearly flat shear modulus reduction and damping curves at small strains regardless of organic content. Cyclic direct simple shear tests on humified material showed a larger pore pressure buildup than found in tests on non-to-moderately humified material. Differences in degree of humification did not result in significant differences in the shear modulus reduction curve, including $G_0$ values. Large scatter was found in the damping curves. For the humified material, tested at low stress level, a discontinuity in the damping curve is found at shear strain of 3%, which corresponds to a rapid pore pressure buildup in the tests.

A new framework is developed to extend an existing small-strain shear modulus $(G_{\max })$ model to determine $G_{\max }$ of unsaturated silty soils along different paths of the soil water retention curve (SWRC) including the scanning loops. The suitability of the proposed framework is validated against experimental results of a series of bender-element tests performed in this study and data reported in literature. Measured values of $G_{\max }$ showed a slight hysteresis in the $G_{\max }$ measurements along the scanning curves of the SWRC, with lower values along the wetting scanning paths. However, results indicated that the value of $G_{\max }$ was recovered once the main drying path was reached. Results of this study also indicated that $G_{\max }$ behavior of the silty specimen along the scanning curves was stress dependent. The model was observed to follow the experimental data along different paths of the SWRC including scanning curves.

There is an increasing tendency for buildings in urban areas to have basements. However, the coseismic behavior of these structures is not well understood. Dynamic centrifuge experiments were performed to investigate the behavior of structures with narrow basements located in liquefiable soils. The tests showed that basements can be used to reduce the liquefaction-induced settlement of structures. However, it may be misleading to model only a simplified geometry of the basement which ignores the realistic, postconstruction geometry. The inclusion of diaphragm walls extending below the bottom of the basement worsened the settlement for heavier structures and worsened the rotation for lighter structures. Digital image correlation provided novel insight into the soil–structure interaction for these scenarios. The inclusion of a continuous wider base slab was found to prevent rotation. The width of the widest section of the basement and the net weight of the structure during liquefaction were found to be the key design parameters to ensure that structures with basements in liquefiable soils accumulated minimal settlement and rotation.

The interaction between surface structures and buried pipes is unavoidable. For instance, placing the pipe at a shallow depth, near to the surface, attracts substantial additional earth pressures due to the external surface loading, causing overstressing or unacceptable deformations of the buried pipe. Several alternatives may be used to mitigate this situation, including using induced trench construction, using lightweight fill material to reduce imposed loads, and finally relocation of the pipe, which is the most expensive and least desirable alternative. The characteristics of the used backfill material control the pipe–soil interaction mechanism and thus the amount of exerted pressures. Using lightweight compressible materials, such as tire-derived aggregates (TDA), above buried pipes has long been investigated to reduce pipe stress. However, such materials may result in undesirable surface settlement that may compromise the pipe performance. In this paper, a coupled TDA–geocell stress-bridging system was developed utilizing six full-scale tests and a comprehensive three-dimensional (3D) finite-element modeling component. The developed system uses a geocell-reinforced top granular backfill layer over the TDA layer to induce a stress-arching mechanism capable of reducing the imposed stresses on the pipe below and control the surface settlement.

A three-dimensional (3D) incremental plasticity constitutive model is developed for simulating the strain softening behavior of soil materials. The constitutive model extends an existing multiyield surface (MYS) plasticity formulation with a new strain softening logic. Formulation of the model is presented, and calibration is undertaken to match an available data set. Implementing the model into OpenSees, finite element (FE) simulations are conducted to highlight the underlying response mechanisms. Strength and stiffness degradation due to the strain softening mechanism is shown to play a substantial role in terms of accumulated deformation and influence on the resulting ground accelerations. For that purpose, computed results with and without the strain softening effect are compared and discussed. As such, incorporation of strain softening is an important consideration for a wide range of scenarios involving sensitive clays, cemented, over-consolidated, very dense, or frozen soils among others. Overall, the derived insights are of significance for seismic loading in such soil formations.

This paper deals with the capacity of bridge abutments, which is an important element for the evaluation of the seismic performance of bridges with integral or semi-integral abutments and yet has received little attention in the scientific literature. We evaluate the capacity of the system formed by the abutment structure, the foundation soil, and the approach embankment under multiaxial loading conditions, based on a finite-element implementation of upper and lower bound theorems of plastic limit analysis. The ultimate conditions, including combined soil-structure failure mechanisms, are expressed by a capacity surface in a generalized force space that can be identified through a limited number of constitutive parameters. This ultimate limit state surface can be used for a direct verification of the abutment in force-based approaches, or it can be included in plasticity-based macroelements to provide a detailed description of the cyclic behavior of the soil-abutment system.

Foundation pinning is a critical consideration for design and analysis of bridge foundations subject to liquefaction-induced lateral spreading, particularly for bridges with a standard approach embankment of finite width. The simplified analysis procedure that has been generally adopted for this case makes consideration for foundation-pinning effects by considering the compatibility between the near-field soil and foundation displacements; however, there is a lack of guidance or evidence indicating the practical limitations of the simplified method. This paper discusses the results of a large parametric study carried out using three-dimensional (3D) finite-element models and simplified analysis models of corresponding site conditions. This study is designed to identify the range of conditions where the simplified method produces reasonable results and to determine the expected reduction in near-field displacements relative to those in the free field for different site geometries such that future applications of the simplified pile-pinning analysis procedure will have a benchmark for comparison.

Results from full-scale physical experiments are reported to quantify the column forces that develop in a modular, polymer stormwater collection structure when buried at its minimum soil cover and subjected to design-truck loads. Columns located directly beneath the load pad experienced the largest increments in force from surface load. Load was also transferred through the soil and the structure to nearby columns. The four central columns carried on average 31% of the applied nominal design-truck load. Column forces from backfilling were found to be only 10% of the response from surface load. Factored column demand at the service design load (107 kN) was equal to 0.45 and 0.64 times the buckling resistance of the 0.6-m and 0.9-m-long columns tested. For the conditions tested, the columns satisfy AASHTO load and resistance factor design requirements against individual column buckling with a resistance factor of 0.7.

A significant challenge for engineers working with peat is the estimation of the undrained shear strength (${\mathrm{s}}_{\mathrm{u}}$). This is particularly the case for shallow, slightly overconsolidated peats found on natural hillsides and at the toe of embankments. Existing laboratory and in situ techniques may not be suitable due to issues such as access to remote areas, the resolution and accuracy of measuring equipment, sampling disturbance effects, and the influence of fibers on the measured results. It is logical to attempt to correlate $s_u$ with shear-wave velocity ($V_s$) because both parameters depend on the same set of fundamental factors. A lightweight portable probe has been developed that can be used to resolve the low $V_s$ values in peat reliably and repeatably. It was not possible to determine $s_u$ directly from the $V_s$ measurements. However, a strong correlation was found between normalized $V_s$ (by water content, $w$) and $s_u$ (derived from direct simple shear tests). A single operator can collect a continuous profile of $V_s$ and $w$ simultaneously and therefore derive a one-dimensional (1D) $s_u$ profile for the full peat thickness. Some limitations in the use of the derived empirical equations are outlined.

The influence of particle shape was evaluated under drained and undrained (constant volume) condition using three-dimensional (3D) cubical assemblies of spheres, ellipsoids, and cluster of spheres (a combination of seven spheres with two different degrees of overlap) with same particle size distribution. It was found that the peak deviatoric stress, the minimum dilatancy ($d={\mathrm{d}\epsilon }_v^p/{\mathrm{d}\epsilon }_q^p$), corresponding stress ratio (${\eta }_{\mathrm{dmin}}$), the bounding surface dilatancy model, and the location of the critical state line (CSL) both in the $e\text{-}\log (p^{\prime })$ and the $q\text{-}{p}^{\prime }$ space were influenced by particle shape. Therefore, four corresponding sets of constitutive parameters for four different particle shapes were implemented in a bounding surface model to predict both drained and undrained (constant volume) discrete element method (DEM) simulation. Good prediction, irrespective of particle shape, indicates that the observed DEM behavior can be adequately captured by the theories of continuum mechanics. Importantly, the majority of the constitutive parameters were influenced by particle shape and can be correlated with simple shape descriptor of sphericity.

A grouting technique is introduced as a measure to protect tunnels adjacent to a large-scale excavation. Field measurements indicated that this grouting technique reduced the maximum horizontal displacement in the tunnel from 9.2 to 4.6 mm. Based on this application and two field tests, the following recommendations are proposed: (1) the upper boundary of the grouted zone should be set at or below the tunnel; (2) grouting holes should be installed 3–4 m from the tunnel and at an interval of the length of a tunnel ring along the tunnel axis; (3) in a row of grouting holes, grouting should be conducted at an interval of six to eight holes in a day, and the grout volume per hole should be small, such as $0.5{\mathrm{m}}^3$; and (4) when using multiple rows of grouting holes, a far-row-first grouting scheme, in which the grouting sequence progresses toward the tunnel, should be adopted.

To date, why a 13-story building in Shanghai fell abruptly to the ground in 2009 remains uncertain. By review of physical evidence, limit-equilibrium analyses, extensive calculations, and three-dimensional numerical simulations, this study reveals that the failure arose from a rainfall-triggered undrained general shear failure of the subgrade underneath the adjacent stockpile rather than previously identified lateral ground movement shearing off piles below the building or failure of piles along the excavation side incurring progressive tilting failure of the building. Deep-seated slip failure of the stockpile applied an impact load on the building and immediately produced an unallowable overturning moment around the south building edge; consequently, the building suddenly fell over southward. Furthermore, the following vital phenomena, which received no attention in the previous investigations, are also explored: (1) how this building fell over but an adjacent building subjected to similar conditions did not; (2) how this building supported by piles fell over but a flood wall supported by shallow foundation remained intact, although both were near a 10-m-high stockpile; and (3) how the flood wall near the 10-m-high stockpile remained intact but the flood wall near a 6-m-high stockpile underwent catastrophic failure. Finally, some design and construction issues involved in this failure case are discussed.

This study presents an application of horizontal spoil discharge jet-grouting (SDJG) columns in soil improvement between the new undercrossing tunnels and the existing tunnels in Changsha, China. To investigate the impact of SDJG construction on the ground and the existing tunnels, the ground pore-water pressure, induced hoop strain, vertical displacement, and rotation of the existing tunnel were monitored. The results indicate that SDJG columns were generally well constructed with an average unconfined compressive strength exceeding 3.50 MPa. Because of the quick discharge of spoils, there was only a slight increase in ground pressure and deformation of existing tunnels during the installation of SDJG columns. The influential range of the SDJG method is much smaller than that caused by pile driving and horizontal twin-jet grouting, and it is similar to that caused by wet deep mixing. SDJG is recommended to improve the area in which adjacent sensitive structures and infrastructures exist because of its reliable effect and minor disturbance to the surrounding ground.

Recent research showed that fracture of sand particles plays a significant role in determining the plastic bulk volumetric changes of granular materials under different loading conditions. One of the major tools used to better understand the influence of particle fracture on the behavior of granular materials is discrete-element modeling (DEM). This paper employed the bonded block model (BBM) to simulate the fracture behavior of sand. Each sand particle is modeled as an agglomerate of rigid blocks bonded at their contacts using the linear-parallel contact model, which can transmit both moment and force. DEM simulated particles closely matched the actual three-dimensional (3D) shape of sand particles acquired using high-resolution 3D synchrotron microcomputed tomography (SMT). Results from unconfined one-dimensional (1D) compression of a single synthetic silica cube were used to calibrate the model parameters. Particle fracture was investigated for specimens composed of three sand particles that were loaded under confined 1D compression. Breakage energy measured from DEM models matched well with that measured experimentally. The paper studied the effects of contact loading condition and particle interaction on the fracture mode of particles using BBM that can closely capture the 3D shape of real sand particles.

Ettringite usually is formed in lime- and cement-stabilized gypseous soils, resulting in significant swelling upon wetting and thereby causing damage to pavements and foundation systems. To reduce the ettringite formation and the associated swelling, magnesia (MgO)-activated ground granulated blast-furnace slag (GGBS) was investigated for stabilizing gypseous soil. Experimental tests, including swelling, unconfined compression strength, X-ray diffraction (XRD), and scanning electron microscopy (SEM) studies, were conducted to examine properties of MgO-GGBS-treated gypseous soil. Test results illustrated that the swelling of MgO-GGBS-stabilized soils (0.4%–2%) was much lower than that of cement-stabilized soil (6.1%), whereas the strength of MgO-GGBS-stabilized soils after soaking (1.2–2.8 MPa) was significantly higher than that of cement-stabilized soil (0.3 MPa). XRD and SEM results showed that no ettringite was formed in MgO-GGBS-stabilized soils, which primarily was responsible for the lesser swelling and higher strength compared with that of the cement-stabilized soil after soaking. Overall, test results indicated the potential of MgO-GGBS for effective stabilization of gypseous soils.