Journal of Geotechnical and Geoenvironmental Engineering

When simulating the vertical drain method using a soil–water coupled finite-element analysis, we the macroelement method can be adopted to provide the water absorption function of drains to individual elements approximately. A previous study added the discharge function of vertical drains to the technique so that the occurrence of well resistance can be considered in accordance with its mechanism. This paper verified the approximation accuracy of this new macroelement method in quasi-static problems. The macroelement method was derived under the assumption that the axisymmetric pore water pressure distribution is equal Barron’s solution, but the first numerical example demonstrated that the technique has high approximation accuracy even for nonaxisymmetric problems by appropriately converting the permeability of a drain. The second calculation example included a number of drains and applied the vacuum consolidation method to clayey ground containing a middle sand layer. In this calculation, there was remarkable well resistance, and pore water flowed from the unimproved region to the improved region or between the effective areas of each drain. The calculation results indicated the superiority of the new macroelement method in terms of accurate approximations even for such a complex problem. Moreover, this study demonstrated the effectiveness of waterproof sealing, a countermeasure for sucking pore water from the middle sand layer, using the new macroelement method.

This paper provides insight into the behavior of a stiffened caisson anchor under inclined cyclic loading in calcareous silt. A series of tests was conducted in a beam centrifuge. A monotonic test was first performed, quantifying the pure monotonic capacity, and then four cyclic loading tests varying the mean load, amplitude, and number of cycles. Cyclic soil characterization T-bar tests and caisson tests were linked. Undrained cyclic T-bar tests led to generate excess pore pressure, resulting in degradation of soil strength and stiffness. For partially drained cyclic caisson tests, the excess pore pressure generated during initial undrained monotonic loading experienced partial dissipation. Healing due to consolidation outweighed the damage due to initial pore pressure generation. Postcyclic monotonic capacity was found to be up to 35% higher compared with the pure monotonic capacity unless the anchor failed during cyclic loading. Measured rotation indicated the evolution of anchor failure mechanism. Caisson capacity under inclined loading was presented as a failure envelope, with the effect of cyclic loading accentuated. The contribution of the soil–chain interaction on the caisson capacity was minimal. No trenching was apparent on the soil surface, and no gap was formed around the anchor in the considered centrifuge testing conditions.

Earthquake-induced soil liquefaction can cause settlement around piles, which can translate to negative skin friction and the development of drag load and settlement of the piles. A series of centrifuge model tests were performed to assess liquefaction-induced downdrag and understand the interplay and effects of (1) pile embedment and pile-head load, (2) excess pore pressure generation and dissipation, and (3) reconsolidation and ground settlement on pile response during and postshaking. The model included a layered soil profile (clay, liquefiable sand, and dense sand) with two 635-mm-diameter instrumented piles. One pile was placed with its tip at the bottom of the liquefiable deposit; the other pile was embedded five diameters into the dense sand layer. The model was shaken with multiple earthquake motions with their peak horizontal accelerations ranging from 0.025 to $0.4g$. For each shaking event, the drag load on the piles first decreased during shaking and then increased during reconsolidation, exceeding its preshaking value. With multiple shaking events, the net drag load on the piles increased. The maximum observed drag load was found equal to the drained interface shear strength calculated from the interface friction angle of $\delta =30°$ and a lateral stress coefficient of $K=1$. Larger drag loads and smaller settlements were observed for the pile embedded deep in the dense sand layer. Most of the pile settlements occurred during shaking; postshaking pile settlement was less than 2% of the pile’s diameter. The mechanisms behind the development of liquefaction-induced drag load on piles and settlements are described. Select ramifications concerning the design of piles in liquefiable soils are also described.

Recently, progress has been made toward understanding the seismic response of structures placed on unsaturated soil layers. A missing link, however, involves the influence and assessment of the underlying soil saturation conditions on the expected superstructure seismic demands. Simplified soil–structure interaction procedures that can be used to predict superstructure seismic demands have not been explicitly extended to incorporate the influence of unsaturated soil on the system response. In this paper, results from a series of six centrifuge tests are compared. In each test, an inelastic single-degree-of-freedom physical model was shallowly embedded in a sandy silt with a distinct water table elevation or a completely dry soil condition. The soil-structure system was subjected to a series of earthquake motions. The response of the system was evaluated to assess the influence of the soil saturation condition on the seismic response. Specifically, a conventional analytical procedure for predicting the influence of inertial interaction on the seismic response of the structure was extended to consider the water table elevation and underlying soil saturation condition and evaluated for its reliability. Analytical flexible-base modal parameters were compared with those determined from experimental results to judge the potential of the analytical procedure to be used in practice. Experimental results suggest that as the water table elevation was lowered from the fully saturated condition, both the flexible-base system period and damping ratio reduced. Therefore, the system behaved stiffer in the unsaturated soil compared with the dry and fully saturated conditions. The stiffer response reduced the seismically induced foundation settlements and rotations but amplified superstructure seismic demands in the form of accelerations, flexural drifts, and bending strains.

Microbial-induced calcium carbonate precipitation (MICP) is a nature-based and eco-friendly technique that has presented promising applications in various disciplines. Despite the extensive amounts of prior studies about this technique, the impact of environmental conditions on the mineral compositions and cementitious characteristics of calcium carbonate precipitations remains unclear. In this study, we focus on four primary factors including temperature (15°C, 25°C, and 35°C), pH of initial solution (7, 8, 9, and 10), bacteria solution (BS) concentration (${\mathrm{OD}}_{600}=0.24$, 0.47, 0.68, and 0.81), and cementation solution (CS) concentration (0.1, 0.25, 0.5, 0.75, 1.0, and 1.25 M). Under these varying conditions, 36 groups of MICP experiments are performed. Material characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and an ultrasonic oscillation test are applied to investigate the morphological features, mineral compositions, and cementitious characteristics of calcium carbonate precipitations, respectively. Experimental results highlight the strong dependence of calcium carbonate precipitations on these factors. The higher temperature contributes to the larger size of calcium carbonate crystal. As the pH of initial solution increases, there is a tendency for mineral composition to change from vaterite into calcite. The decreased BS concentration increases calcite contents and enhances the cementitious characteristics of the precipitation. The CS concentration level influences the size of the calcium carbonate crystal. Through a systematical analysis of how various factors jointly influence the crystal precipitations, this study is expected to improve the current understanding of the MICP process, and contribute to the future optimized design of biomediated soil improvement.

Recently, isolated foundations with cushions have gained more attention in bridge design, especially for cross-sea bridges in deep water 50 meters or more in depth. This foundation has become a good choice for bridges built in seismic active zones. Along with interactions within the cushion layer, interactions between the caisson foundation and composite cushion are crucial for isolated foundations. Unfortunately, the shear characteristics of the cushion–structure interface under monotonic and cyclic loading have not been well evaluated. In this study, a series of monotonic and cyclic large-scale shear tests were conducted to investigate the behavior of the cushion–structure interface using crushed aggregates and pebble gravel as the cushion, respectively. The tests showed that the particle morphology properties have significant correlations with the cushion–structure interface’s shear behavior. Some shear characteristics of the larger grain size’s cushion–structure interface, such as cushion clogging and the effect of particle breakage were analyzed based on the developed tests. The shear stress, isolation effect, shear modulus, and damping ratio of the composite cushion–structure interface were different from that of the single-layer cushion–structure interface, which was primarily due to the pebble gravel. The relative thickness of the pebble gravel layer also influenced the shear characteristics of the composite cushion–structure interface. As the relative thickness of the pebble gravel layer decreased, the isolation effect, shear stress, shear modulus, and damping ratio of the composite cushion–structure interface increase.

Estimation of nonlinear pile settlement can be simplified using one-dimensional “$t\text{-}z$” curves that conveniently divide the soil into multiple horizontal “slices.” This simplification reduces the continuum analysis to a two-point boundary-value problem of the Winkler type, which can be tackled by standard numerical procedures. Theoretical “$t\text{-}z$” curves can be established using the “shearing-of-concentric-cylinders” theory of Cooke and Randolph-Wroth, which involves two main elements: (1) a constitutive model cast in flexibility form, $\gamma =\gamma (\tau )$; and (2) an attenuation function of shear stress with radial distance from the pile, $\tau =\tau (r)$. Soil settlement can then be determined by integrating shear strains over the radial coordinate, which often leads to closed-form solutions. Despite the simplicity and physical appeal of the method, only a few theoretical “$t\text{-}z$” curves are available in the literature. This paper introduces three novel attenuation functions for shear stresses, inspired by continuum solutions, which are employed in conjunction with eight soil constitutive models leading to a set of 32 “$t\text{-}z$” curves. Illustrative examples of pile settlement calculation in two soil types are presented to demonstrate application of the method.

The rheological behavior of soil–water mixtures can affect the flow dynamics of natural processes such as flow-type landslides and sediment transport. In this study, an experimental investigation was carried out on soil–water mixtures containing particles up to 0.425 mm with volumetric solid concentrations of $0.05\le C_V\le 0.35$ using a wide-gap rotational viscometer, and the contributions of particle–fluid, collisional, and colloidal interactions to their rheological behavior were evaluated thoroughly. The torque-scaling method was applied to identify the flow regime and extract the effective rheological parameters from turbulent flows. A transition between dilute and concentrated mixtures can be identified based on their sediment type, $C_V$, and the predominance of particle–fluid and interparticle interactions. For dilute mixtures ($C_V<0.25–0.28$) the particle-fluid interaction is dominant. The colloidal interactions induce another force scale that is independent of the shear rate. Thus, the Bingham model can be applied to such mixtures (debris or mud flood). For concentrated mixtures ($C_V>0.25–0.28$), the shear-thickening rheology can be applied for granular mixtures (debris flows), because the collisional interactions are dominant, whereas shear-thinning rheology can be applied for fine-grained mixtures (mudflows), because colloidal interactions are dominant.

The design of on-bottom pipelines regarding thermally induced lateral buckling requires a comprehensive understanding of large deformation lateral pipe–soil interactions to ensure that lateral buckles form as planned. This paper presents a numerical investigation into the lateral loading behavior of a pipe on undrained clay using sequential limit analysis. The lateral displacement experienced by the pipe is up to eight pipe diameters to capture the residual behavior. Validation against published centrifuge tests in terms of pipe invert trajectory and lateral soil resistance is achieved before a detailed parametric study is presented. Lower and upper bound estimates of the critical pipe weight that differentiates light from heavy pipe behavior are derived. Analytical equations are then developed to predict the lateral residual resistances, accounting for the influence of pipe weight, initial embedment, strength gradient, unit weight, and strain softening effect, and the predictions compare very well with a number of model test results.

The kinematic bending and filtering potential of a fixed-head pile are explored when large shear strains are generated in the surrounding soil during the passage of seismic waves. The problem is treated numerically by employing a freely available 1D code to derive soil response at free-field conditions and an advanced 3D finite-difference (FD) model of the soil-pile system. Three idealized soil profiles with varying stiffness and strength and a real layered site are considered under earthquake excitations of increasing intensity, allowing investigation of the pile’s non-linear kinematic response under shear strains exceeding the threshold of an equivalent-linear approximation. Simple analytical solutions are revisited in the context of soil response close to failure, by means of the FD solution, and an equivalent linear approach is proposed for assessing kinematic pile-head bending and filtering action in the presence of large earthquake-induced shear strains in the soil and non-linear pile behavior. A practice-oriented procedure requiring only a pertinent 1D soil response analysis is proposed to address kinematic effects in seismic design of piles.

This paper proposes a new approach for incorporating the positive attributes of the small-strain shear wave velocity ($V_S$), stress-based simplified procedure and the cyclic strain procedure into penetration test, stress-based simplified liquefaction triggering models, with the objective of more fully accounting for the influence of intrinsic soil properties and soil state variables on liquefaction triggering. Current simplified liquefaction procedures are limited in their ability to capture the effects of intrinsic properties (grain size, mineralogy, grain shape, etc.) and the state properties (stress state, void ratio, fabric, etc.). To overcome these limitations, a new mechanistically based $K_{\gamma }$ factor is proposed that can be incorporated in penetration test, stress-based simplified liquefaction triggering models in place of the currently used $K_{\sigma }$ factor. However, $K_{\gamma }$ is conceptually very different from $K_{\sigma }$. While most $K_{\sigma }$ relationships have largely been empirically based and relate to the soil’s cyclic resistance to liquefaction, $K_{\gamma }$ is more mechanistically based and relates to the loading imposed on the soil. Specifically, $K_{\gamma }$ is based on equating the shear strain induced in a given soil at given initial stress state and subjected to a given shear stress to the induced shear strain when the soil is confined at a reference initial stress state, all else being equal. Analyses show that $K_{\gamma }$ is able to capture the liquefaction triggering behavior in both lab and field data in a wide range of soils and stress states. Numerically, $K_{\gamma }$ and $K_{\sigma }$ are similar for young, normally consolidated sandy soils when the factor of safety ($FS$) against liquefaction triggering is close to one, but may differ significantly for other scenarios and/or conditions. This has important implications for probabilistic-based analyses which consider a range of shaking intensities imposed on the soil, not just the case where $FS=1$.

Mudflows from the ongoing eruption of a mud volcano near Sidoarjo (East Java, Indonesia) have continued for more than 15 years and now cover an area of $8.2{\mathrm{km}}^2$ to a depth of more than 15 m. The mudflows are contained within a system of perimeter earthen levees/dykes that were constructed as a series of temporary defenses. The levees have marginal stability and limited freeboard due to the low shear strength and high compressibility of the 25-m-deep soft clay foundations, which have already resulted in ground deformations exceeding 7 m. In this paper, we analyze the deformations and stability of the downstream staged construction at a critical reach in order to (1) understand causes of a recent failure (2018); and (2) assess the current state of the levee following completion of a fifth construction stage (2019) that included a 35-m-wide, 4-m-high stabilization berm with an array of prefabricated vertical drains (PVDs) to accelerate consolidation. Our analyses used large-deformation elastoplastic finite-element analyses to simulate consolidation and lateral spreading of the foundation soils due to levee construction and mudflow loads. Levee stability was evaluated using numerical limit analyses for the deformed geometry and simulating changes in undrained strength with the consolidation state and direction of shearing at each stage of construction. The results were consistent with the magnitudes of the observed levee settlements and mechanism of failure; they also show the potential for an additional $>2\mathrm{m}$ settlement over the next 5 years, even without considering creep of the clay or larger-scale processes controlling subsidence around the volcanic caldera. Future construction stages to contain the expected mudflow will require improvement of the mechanical properties of the alluvial clay to ensure adequate long-term freeboard.

Thermomechanical behavior of soils has attracted great attention in recent years because of its great importance in some emerging geotechnical applications such as energy piles. So far, the thermoplasticity (e.g., the influence of temperature on the yield surface) has been well understood, but the thermoelasticity has not been purposely studied. In this study, a temperature-controlled oedometer equipped with bender elements was developed and then used to mainly investigate effects of temperature and thermal cycles on the elastic shear modulus ($G_0$) of a saturated lateritic clay. In addition, one test was performed on kaolin clay to investigate the influence of thermal cycles on $G_0$. Two types of thermomechanical paths were considered at different temperatures and stresses, including constant-temperature loading–unloading and constant-stress cyclic heating–cooling. Results from these tests consistently reveal that at a given stress, $G_0$ is smaller at a higher temperature. This can be attributed to the reduction of interparticle force during the heating of saturated clay, according to the double layer theories. Furthermore, $G_0$ of the lateritic clay increases by about 12% and 16% after four thermal cycles for overconsolidated and normally consolidated specimens, respectively. This can be due to soil densification and particle rearrangement during the heating–cooling cycles. These results are useful for improving the modeling of thermoelasticity and also for the analysis of thermally active structures such as energy piles.

Adding fiber to reinforce soil is a technique widely used at geotechnical works due to the possibility of a considerable increase in soil’s mechanical properties. One way to evaluate such improvement is to compare the features before and after the addition, utilizing the unconfined compressive strength (UCS) test. However, the results of this test can be biased by soil variability, fibers characteristics, and test errors. The objective of the present work is to analyze which variable most influences the results of UCS tests and evaluate the relationship between the soil strain and its strength alterations due to fiber. In this way, the extended chi-square automatic interaction detector (CHAID) method was adopted on UCS samples obtained from a database established from papers, theses, and dissertations. This process concluded that the type of fiber used is the variable with the highest significance among the studied ones. Furthermore, the regression of the polypropylene (PP) demonstrated a linear tendency and a strong correlation coefficient, validating the hypothesis that the sample’s strength has an immediate relation with its strain.