Journal of Geotechnical and Geoenvironmental Engineering

A series of cyclic triaxial tests are performed on a number of intact soils sampled from various sites to examine their liquefaction behavior in terms of energy. Although several laboratory tests on reconstituted specimens carried out in cyclic simple shear tests have already shown that liquefaction behavior is uniquely determined by cumulative dissipated energy during cyclic loading irrespective of stress-time histories, it is found here that the energy capacity for liquefaction tends to vary depending on the cyclic stress ratio (CSR) or number of cycles for liquefaction ($N_L$) in triaxial tests on intact soils of higher cyclic resistance ratio (CRR) in particular. This is found to be specific to cyclic triaxial tests wherein axial strains tend to grow larger on the extension side than on the compression side. In overcoming this unfavorable trend in view of in situ simple shear stress condition, a unique correlation between the energy capacity and CRR for $N_L=15$ or 20 is developed by utilizing the test results, so that the liquefaction energy capacity to be used in the energy-based method (EBM) can be readily evaluated from CRR irrespective of soil types.

Cohesion between grains in a geological system is perhaps the simplest and ideal representation of a range of material systems including soft rocks, structured soils, mudstones, cemented sands, powder compacts, and carbonate sands. This presence of inter granular cohesion is known to alter the ensemble mechanical response when subjected to varied boundary conditions. In this study, a hollow cylinder apparatus is used to investigate the mechanical behavior of weakly cemented sand ensembles by mapping the state boundary surfaces including the failure surface (locus of peak stress state) and the state of plastic flow (locus of final stress state). When these materials are sheared, the plastic deformation accumulates due to breakdown of cohesion between the grains, which introduces a lag in occurrence of peak stress ratio and maximum dilatancy, unlike a typical frictional granular material. This breakdown of cementation is affected by changes in the initial mean effective stress, initial reconstitution density, and intermediate principal stress ratio (stress path on the octahedral plane). The final state locus, emergent at large strains, was found to depend on the initial reconstitution density. Further, the parameters are extracted for calibration and prediction exercise using an elastic plastic constitutive model. In this and several other models, the effect of cementation is considered as an additional confinement to the ensemble. Such an approach predicts the stress state precisely but does not predict the volumetric response accurately, especially at large strains.

This paper investigates the structural behavior and soil–structure interaction mechanism of a three-sided culvert (TSC) at service and ultimate load levels. Field measurements were used to verify a two-dimensional (2D) finite-element model (FEM) and evaluate the backfill height at which the TSC would fail. In addition, experimental data available in the literature of an arched TSC segment loaded to failure was adopted to verify a three-dimensional (3D) FEM for the analysis at the ultimate limit state (ULS). The results demonstrated that the Canadian Highway Bridge Design Code overestimates the earth pressures on the top slab. It was also found that the connection at the sidewall base does not behave as a perfect hinge. Finally, the nonlinearity of the reinforced concrete (RC) was evaluated throughout the loading spectrum and it was concluded that simplifying the behavior of RC using a linear-elastic model is only adequate at the service load levels.

Two-dimensional, nonlinear, finite-difference analyses were used to investigate the stability of an embankment supported by spatially variable soil–cement columns. This study evaluated the improvement/merit of employing stochastic modeling approaches, such as spatially correlated random fields, relative to deterministic analysis, which commonly neglects spatial variability. The spatial variability, which is specified by mean, coefficient of variation (COV) and autocorrelation distance ($R$), can significantly influence the performance of the treated in situ soils and the overlying structure. Reliability analyses with three types of spatial variable soil–cement columns were conducted using a COV value of 0.6 for the soil–cement strength, and the effects of the autocorrelation distance were evaluated. Gaussian spatially correlated random field models (stochastic models) with 100 realizations for each case were used in a strength-reduction analysis to determine the failure surface and safety factor. Results of the models with uniform material properties were compared with each of the stochastic model realizations. ANOVA was used to analyze the statistical difference between the means of safety factors. The stochastic distributions of safety factors and consequences of spatial variability on the failure mode of columns and embankment, and implications for engineering practice were discussed.

Collapsible unsaturated soils experience large volumetric compressive deformations upon wetting. Soil collapse is a geotechnical problem that occurs in different regions of the world and profoundly impacts buildings and civil infrastructure constructed on this type of soil, with the associated impact on safety and economy. Compaction is a simple, relatively cheap, and yet effective soil improvement technique that could significantly reduce soil collapsibility. This paper combines laboratory tests, in-situ investigations, and numerical modeling to gain a better understanding of the effect of soil compaction on collapsible-soil settlements upon wetting under field conditions. The finite elements program CODE_BRIGHT was adopted for the numerical simulations of the field tests using model parameters that were previously obtained from independent laboratory experiments. The laboratory campaign comprised suction-controlled oedometer and triaxial tests of the natural and compacted soils considered in this study, as well as permeability and water retention experiments. The numerical simulations show that the proposed approach can model the behavior observed in the in-situ tests involving footing prototypes on collapsible soils subjected to soaking. These analyses also demonstrate that soil compaction is a viable technique to reduce collapsibility in order to meet predefined maximum allowable settlements. Additional analyses were carried out to extend the main findings to other soils and loading conditions. Based on stress-bulb concepts, a method is proposed to reduce settlements in collapsible soils for typical footing operational conditions.

In recent years, there has been a significant push to develop optimized pile designs in the offshore industry, driven by the growth of offshore wind. One of the largest remaining uncertainties governing axial pile design in sands is the influence of ageing effects and how an aged pile responds under axial cyclic loading. This paper presents results from a long-term campaign of field tests on pile ageing and axial cyclic loading in sands, undertaken at the Blessington geotechnical test site in Ireland. Five open-ended driven steel piles were subjected to a total of 33 static and cyclic tension pile load tests undertaken over a 3-year period. The tests were planned and coordinated in order to accurately quantify the effects of ageing and cyclic loading on the pile shaft capacity over time. The tests showed that significant gains in pile shaft capacity occurred over time as a result of pile ageing, in line with results presented by other researchers. Piles subjected to cyclic tension loading remained stable under cyclic loading at load levels much larger than their 1-day capacity. The 1-day capacity appears to offer a lower bound for the degraded pile capacity following tension cyclic loading to failure. The reduction in capacity caused by cyclic loading to failure was related to the pretest increase in capacity caused by ageing. The findings from these field tests in addition to reinterpretation of previous testing indicated that previously published cyclic interaction boundaries may be overly conservative.

Excavation induces stress changes and soil movement on existing floating piled rafts and elevated pile groups. Limited investigation of the effects of deep excavations has resulted in an incomplete understanding of pile foundation performance at the serviceability state. A series of three-dimensional (3D) centrifuge model tests and numerical simulations are conducted in this study to investigate the influence of raft contact on the response of an existing $2\times 2$ piled raft in comparison to that of an elevated pile group when subjected to an adjacent multipropped deep excavation in dry sand. After rising $g$, an applied axial load was supported by 18% by the raft and 82% by the piles in the piled raft foundation prior to excavation. Owing to stress release and soil movement caused by the 8-m-deep excavation, the pile head load increased by 21% and 3% for the pile closer to the excavation for the piled raft and pile group foundations, respectively. Analysis of pile–soil relative settlement and raft contact pressure shows that a gap formed between the raft and ground surface in the piled raft, resulting in a load transfer from the raft to the embedded piles. A 20% larger settlement was seen in the piled raft foundation than in the pile group, to further mobilize shaft and end bearing resistances for the maintenance of vertical equilibrium. Moreover, 30% additional pile bending moment was induced due to excavation.

Three different batches of “standard” Ottawa 20-30 sand were biocemented using enzyme-induced carbonate precipitation (EICP). The specimens from each batch were treated using the same biocementation procedure. The unconfined compressive strength (UCS) of the treated specimens varied from 0.22 to 1.6 MPa depending on the batch of sand used to prepare the specimens. These results show that sand of the same predominant mineral composition (e.g., $>98\%$ silica), of the same grain size distribution, and from the same geological formation but from different quarries within the formation do not necessarily respond in the same manner to biocementation. Hence, standard sands for mechanical geotechnical testing should not be considered a priori to be a standard sand for biogeotechnical testing.