Journal of Geotechnical and Geoenvironmental Engineering

The factor of safety (FS) of levees and floodwalls with relief wells to underseepage is predicated on the blanket thickness and relief well performance. In urban environments with limited right of way, relief wells are an option for addressing underseepage and sand boil development. Instead of adding more wells if problems persist, this study investigates the potential of active pumping at relief wells as an alternative to increase levee and floodwall factor of safety against underseepage. Optimization of relief well operations is achieved by a multiobjective mixed-integer nonlinear programming (MOMINLP) approach. The relief well operations optimization is demonstrated at the Inner Harbor Navigation Canal (IHNC), New Orleans, Louisiana, near the Seabrook Bridge at Lake Pontchartrain. Relief well evaluation at the water level corresponding to the 500-year return storm shows high total head at most IHNC West relief well sites. Relief well operations optimization provides decision makers useful tradeoffs between averaged FS deficit, total pumping rate, and the number of pumping wells for making pumping decisions. This study found that the Pareto-optimal solutions provide reasonable pumping rates, where all of the midway between relief wells in the IHNC West may meet the requirement $\mathrm{FS}>1.5$. The study also found that minimizing the number of pumping wells and minimizing the total pumping rate are influential objectives for deriving efficient pumping strategies. Sensitivity analysis on IHNC water stage found that FS improvement becomes marginal after total pumping rate reaches a threshold, especially at low IHNC water stages.

Adding fiber reinforcement to a loose sand alters the effective stress of the sand skeleton. The rate of pore water pressure build-up when undrained is reduced, and liquefaction may be delayed or prevented. Here the results of cyclic triaxial tests are presented that show this benefit. They are interpretated so the load carried by the fibers is separated from that carried by the pore water and sand skeleton. A newly defined pore pressure ratio demonstrates when the pore water pressure build-up is insufficient for liquefaction to occur. The rule of mixtures is used, along with separate constitutive laws for the sand skeleton and fibers. Account is given to the anisotropic fiber orientation distribution, by which the fibers affect the sand skeleton differently during compression and extension cycles. It is found that the stress state of the sand skeleton remains bounded by critical state strengths after many cycles, as is the case for unreinforced sands. Not correctly determining the load carried by the sand skeleton and adopting the conventional rather than a new pore pressure ratio makes the fiber reinforcement technology appear less effective at suppressing liquefaction than it actually is. This may, unfairly, hinder its uptake in industry.

Vibratory sheet pile driving is a widely used foundation method. In order to investigate the effect of different operational parameters, such as vibration frequency and eccentric moment on sheet pile to ground interaction, carefully monitored and documented field tests were performed. A single sheet pile was vibrated into a sandy soil deposit (esker) and different operational parameters were varied. The interaction between the vertically oscillating sheet pile and the surrounding ground was studied, using sensors on the vibrator and on the ground in the vicinity of the sheet pile. The effect of vibration frequency and eccentric moment on sheet pile penetration speed and emitted ground vibrations is presented. When the sheet pile is vibrated at the resonance frequency of the vibrator–sheet pile–soil system (system resonance), ground vibrations increase significantly and sheet pile penetration speed decreases. It is concluded that the vibration frequency is an important parameter for the efficient and environmentally safe installation of sheet piles. These tests provide insight into the interaction of a vibrated sheet pile and the surrounding ground. Based on these results, guidelines for the efficient and environmentally friendly installation of piles and sheet piles are proposed.

During winter, energy piles are subjected to cooling cycles due to the cyclic operation of the ground source heat pump (GSHP). The cyclic operation of the heat pump causes the energy pile to contract and expand axially and radially, affecting the soil–pile interaction. The effects of cooling cycles on the thermomechanical behavior of energy piles have not been fully investigated. A fully instrumented model concrete energy pile was installed in dry sand and subjected to cooling cycles. Cooling was achieved by circulating a heat exchange fluid with a target inlet temperature of 20°C lower than the initial temperature of the soil ($\mathrm{\Delta }T=-20°\mathrm{C}$). Following the application of thermal loading, pull-out axial load tests were performed to evaluate the effects of cooling cycles on the load–displacement response of the energy pile. Baseline (room temperature), 5-cooling-cycle (5CC), and 100-cooling-cycle (100CC) tests were performed and summarized in this paper. During the thermal and mechanical load applications, temperature in the soil and the pile, axial strains, radial strains, and radial pressures at the soil–pile interface were measured. For the $1g$ scaled energy pile and test conditions (pile in dry sand subjected to cooling cycles with $\mathrm{\Delta }T=-20°\mathrm{C}$), the peak pull-out loads decreased by 32% and 38% for the 5CC and 100CC tests, respectively.

Old Bay Clays are silty clays of Pleistocene age encountered along the margins of San Francisco Bay, beneath various sand formations, Holocene Bay Muds, and surficial fills. These materials are overconsolidated in their natural state. A recent project, Millennium Tower, produced intervals of loading in the Old Bay Clays that induced primary consolidation followed by secondary compression. A testing program was undertaken to characterize secondary compression characteristics of these materials for two conditions: (1) following primary consolidation in the virgin compression range, and (2) following unloading to modest overconsolidation ratios (associated with groundwater rebound and potential foundation modification). Following post-unloading swell of the soil, the rate of secondary compression slows relative to the initial (i.e., subsequent to primary consolidation) condition. We observed three approximately linear intervals of progressively faster compression rates in log time space, with the reset (or zero) time taken upon load application causing the preceding virgin compression. Two models of secondary compression response from the literature are unable to capture this general pattern of response. In one case, the model takes secondary compression rate with respect to log time as invariant; in the other case, the time variations of this rate do not match the data. This work presents a framework that captures this behavior.

Current engineering practice employs clean sand–based procedures to evaluate liquefaction triggering in nonplastic, coarse-grained soils and low-plasticity, fine-grained soils below level or mildly-sloping ground. Furthermore, existing empirical liquefaction triggering procedures treat all clean sands (fines content $<5\%$) as identical (i.e., employing a single liquefaction resistance boundary). To improve these practices, this paper presents a new ${\mathrm{\Delta }}_Q$ common-origin method to assess level-ground liquefaction susceptibility and triggering for cone penetration test (CPT)–compatible soils ranging from nonsensitive clays to clean sands using the soil classification index ${\mathrm{\Delta }}_Q$ (described elsewhere). This procedure was developed using 401 documented case records of liquefaction and nonliquefaction in clean sands, silty sands, sandy silts, and low-plasticity fine-grained soils combined into a single data set. Importantly, the proposed procedure implicitly couples the evaluation of liquefaction susceptibility and triggering and does not require estimating fines content or converting measured CPT tip resistance to an equivalent clean-sand value. Rather, the proposed procedure yields unique estimates of liquefaction resistance for soils based on compressibility (as reflected in ${\mathrm{\Delta }}_Q$) such that factors that affect penetration resistance (e.g., mineralogy, grain shape, density, overconsolidation) are incorporated. The new deterministic and probabilistic procedures are illustrated using examples of liquefaction and no liquefaction in clean sands, silty sands to sandy silts, and low-plasticity fine-grained soils.

Fall cone tests provide simple and rapid estimate of undrained shear strength ($s_u$) of fine-grained soils at various water contents. The accuracy of such $s_u$ estimation depends greatly on the selection of a fall cone factor $K$ that relates the final penetration depth $h_f$ with $s_u$. Available prediction methods for $K$ often fall short of capturing the exact mechanics involved in fall cone penetration. This leads to significant uncertainties in $s_u$ estimation, particularly for a cone angle of 30°. Finite element analyses (FEAs) employing a coupled Eulerian-Lagrangian technique can successfully simulate the evolution of soil resistance around a cone penetrating through soil. Based on the results obtained from a series of FEAs, this paper presents a fall cone-bearing capacity factor that accounts for strain-rate dependent strength gain in fine-grained soils, soil inertia during undrained cone penetration, and nonzero cone velocity at the start of penetration. The effects of strain rate and cone-soil interface roughness condition on $s_u$ are quantified. Numerical predictions demonstrate good agreement with results obtained from fall cone and vane shear tests in Kaolin and Marine silt and with the data available in the literature.

Understanding the evolution of dynamic properties of sand subjected to induced anisotropy is indispensable for an accurate seismic analysis of geostructures. In this study, several bender element and hollow cylinder experiments along various anisotropic stress paths are performed on two types of sands to evaluate the soil dynamic properties over a wide range of small to large strain levels. Accordingly, the influences of both the major principal stress direction ($\alpha$-direction) and the intermediate principal stress, $b=({\sigma }_2-{\sigma }_3)/({\sigma }_1-{\sigma }_3)$, are examined. The data suggested that $\alpha$-direction affects both stiffness and damping ratio, especially at higher confining pressures. However, $b$-parameter has little influence on stiffness and a fairly negligible impact on damping ratio. Based on the experimental results, an empirical model published in the literature is extended by introducing correction factors so as to incorporate the significant contribution of induced anisotropy into the predictions of shear stiffness and damping ratio of sands.

When exploration depth is shallow or site access is limited, a dynamic lightweight penetrometer is an attractive alternative to large penetrometers. Cone resistance, regardless of the penetration test, is influenced strongly by soil conditions: dry unit weight, overburden stress and water content of the surrounding soil, and fines content. This study explored the effects of these parameters on the cone resistance is in a calibration chamber. A series of tests was conducted in clean sands and mine tailings materials, subjected to different overburden stresses and prepared to different void ratios and degrees of saturation. It was found that dry unit weight and overburden stress significantly increases cone resistance. The effects of water content on cone resistance were more significant in mine tailings materials than in clean sands. An overburden correction factor for a dynamic lightweight penetrometer is proposed based on soil conditions, including fines content. Differences from common correction factors used for large penetrometers were observed, and were attributed to the type of soil and range of overburden stress explored in this study.

Coal mines produce large amounts of excavated waste soils, known as spoils. These materials can cover vast areas, are typically dumped in heaps without any treatment, and are difficult to exploit for engineering purposes because of their significant variability. Efficient exploitation of spoil heaps poses engineering challenges, related mainly to the involved degree of uncertainty. A small number of studies have attempted to characterize the geotechnical properties of spoil material; however, there remains a considerable gap in understanding how to deal with spoil materials in the context of sustainable development and civil infrastructure design. In this work, a systematic effort is made to quantify the uncertainty of the geotechnical properties of a particular spoil heap. Laboratory test results based on an extended investigation of a spoil material originating from lignite coal mines are gathered in one database and thoroughly analyzed. The results reveal and quantify the significant spoil material variability, which is contrasted against data for common soils, while a systematic approach is proposed for spoil material characterization.

Characterization of tensile strength is critical to investigate the influence of desiccation and tensile cracks on the structural integrity of natural and artificial earthen structures and slopes. Although several models for the prediction of tensile strength of unsaturated soils have been proposed in the literature, critical gaps remain regarding a comprehensive model describing the tensile behavior of all soil types over a wide range of suction. This paper presents a general model for the tensile strength characteristic curve (TSCC) which establishes a relationship between the tensile strength versus water content in unsaturated soils. The proposed model is applicable to various soil types ranging from clean sands to silty and clayey soils. Tensile strength is characterized using the suction stress concept, and the TSCC model is built upon the concept that changes in tensile strength with water content (or degree of saturation) are primarily dominated by two distinct water retention mechanisms of capillarity and adsorption. Differences in the characteristics of capillary and adsorptive mechanisms and interparticle forces cause dissimilarities in the resultant TSCC in different soil types. Thus, a two-part suction stress characteristic curve (SSCC) was incorporated into the development of the TSCC to separately account for and distinguish interparticle forces and the resultant tensile strength under capillary and adsorptive mechanisms. The model was validated against laboratory-measured tensile strength reported in the literature for 10 soils, and was found to capture the tensile behavior of sandy, silty, and clayey soils well. Compared with several alternative models, the predictive accuracy of the proposed model was greater, particularly for clayey soils at low water contents (high suction). This superior performance can be attributed to properly accounting for the effect of adsorption mechanism, which is significant in clays.

A field trial evaluated the potential of microbially induced calcite precipitation (MICP) through urea hydrolysis for ground stabilization. A bioaugmentation approach was employed in which locally enriched bacteria were injected, followed by an amendment solution containing urea and calcium chloride. Results from cone penetration tests and soil analysis were inconclusive about the obtained ground stabilization. In situ monitoring results were analyzed using a two-dimensional (2D) numerical reactive transport model to evaluate the process performance, in which the effective thickness of the treated layers, the average reaction rate, and a dilution factor accounting for the water extracted from the less-permeable layers were varied, and the results of the different numerical simulations were compared with the field measurements. The combined results of monitoring and numerical modeling demonstrated that treatment was limited to approximately 5% of the total soil volume. The conversion efficiency was significantly lower than expected, and the substrates spread farther than originally intended, which could be attributed to the heterogeneous soil profile with a large amount of fines, causing preferential flow through the more-permeable layers and possibly hydraulically induced fractures.

The compressive behavior of soils at stresses high enough to induce particle breakage is relevant to several geotechnical applications. At these high stresses, compression curves become independent of initial density and define a limiting compression curve (LCC) that follows a power law and depends on particle characteristics. This study focuses on the effect of the particle size distribution (PSD) and particle shape on the LCC. Eleven siliceous, sand-sized mixtures were subjected to one-dimensional compression tests at vertical effective stresses ranging from 10 to 190 MPa. Because particle size affects breakage characteristics, all mixtures had a median particle size of 0.6 mm. This enabled a clear distinction between PSD and particle shape effects while minimizing particle size effects that may obscure trends. There is a direct and linear correlation between the slope and reference stress of the LCC that was previously unknown. Particle shape and PSD significantly affect particle breakage. Particle shape was the single most important predictor of the three parameters that define an LCC: slope, reference stress, and the merging stress at which the LCC begins.