Journal of Geotechnical and Geoenvironmental Engineering

A static lateral load test was performed on a full-scale pile group to determine the resulting pile-soil-pile interaction effects. The 3 × 3 pile group at three-diameter spacing was driven into a profile consisting of soft to medium-stiff clays and silts underlain by sand. The piles were instrumented with inclinometers and strain gages. The load carried by each pile was measured. A single pile test was conducted for comparison. The pile group deflected over two times more than the single pile under the same average load. Group effects significantly reduced load capacity for all rows relative to single pile behavior. Trailing rows carried less than the leading row, and middle row piles carried the lowest loads. Maximum moments in the group piles were 50–100% higher than in the single pile. P-multipliers were 0.6, 0.38, and 0.43 for the front, middle, and back row piles, respectively. Good agreement between the measured and computed pile group responses was obtained using the p-multiplier approach. Design curves are presented to estimate p-multipliers over a range of pile spacings.

A silty sand is considered as a delicate composite matrix containing a sand-grain-matrix and a silt-matrix. Large strain undrained shear strength (S_us) data in triaxial compression for a particular host sand mixed with different amounts of nonplastic fines are presented. Results indicate that the intergranular void ratio, e_s, which is the void ratio of the sand-grain-matrix [given by (e+fc)/(1 −fc), where fc is the silt content fraction by weight], plays an important role on S_us of silty sands. At the same void ratio, e, a silty sand shows low S_us compared to that of the host sand. However, when compared at the same e_s, provided that it is less than the maximum void ratio of the host sand, e_max,HS, both the silty sand and the host sand show similar S_us that is fairly independent of the initial confining stress. When e_s of the silty sand is in the vicinity of or exceeds e_max,HS, the S_us depends on the initial effective confining stress. At such “loose” states, S_us normalized with respect to the initial consolidation stress, $(S_{\mathrm{us}}/{\sigma }_{\mathit{v}o}^{\prime })\text{,}$ is very low and it decreases with a further increase in e_s. At a fines content greater than about 30%, a silty sand or sandy silt is expected to behave as a silt at an interfine void ratio, e_f, defined as the void ratio of the silt-matrix (given by e/fc), unless the silty sand or sandy silt is very dense. A criterion is presented for the undrained shear strength behavior of silty sands in terms of relative percent compaction for field applications. Preliminary recommendations are presented for the choice of undrained strength for seismic stability evaluation against large deformations.

Naturally cemented materials often have inherent variabilities in density and degree of cementation. The influence of this variability on the properties of cemented materials is investigated by producing artificially cemented specimens at dry unit weights ranging from 12 to 19 kN/m³ and gypsum cement contents ranging from 0% to 20%. Tests have been performed to investigate the index strengths, the behavior in isotropic and K₀ compression, and the responses from standard triaxial compression tests over a wide range of confining pressures. The index properties, and the compression and stiffness parameters of the cemented sands are presented, with particular attention given to the influences of density and degree of cementation. For the artificial soil, the effects of the bonding are only significant for stresses below an apparent preconsolidation stress. The strength and stiffness increase with increasing density and cement content, but the influence of the cementation decreases as the density increases.

A centrifuge-testing program is conducted to assess the earthquake performance of countermeasure retrofit techniques for a liquefiable foundation under an existing embankment. Currently, such testing results offer a valuable alternative to actual full-scale dynamic response, which is virtually nonexistent for retrofitted embankments. The response of a cohesive highway embankment supported on a loose saturated sand layer is analyzed under dynamic base excitation conditions. In a series of five separate model tests, this embankment-foundation system is studied first without, and then with the following four different liquefaction countermeasure techniques: densification, cement deep-soil-mixing, gravel berms, and sheet-pile enclosure. The underlying mechanism and effectiveness of each countermeasure are discussed based on the recorded dynamic response. Effects of each countermeasure on both foundation excess pore pressures and embankment deformations are analyzed and compared. The implemented countermeasures are found to reduce embankment vertical deformations by a maximum of about 50%. However, in some cases cracking and lateral spreading of the embankment are practically eliminated. Thus, retrofit techniques that constrain lateral flow of the underlying liquefied soil are deemed to be particularly effective in preserving overall embankment integrity.

This paper presents a case study concerning the design and construction of structural and nonstructural slurry walls at the Dam Number 2 Hydropower Project (project) on the Arkansas River. One-hundred four 2.8 m (9 ft, 2 in.) long by four 4.0 m (13 ft) long T-shaped structural slurry wall panels, which included some of the heaviest reinforcing cages ever lifted into place as a single unit, were used along with 24 2.8 m (9 ft, 2 in.) long straight structural slurry wall panels to construct the upstream and downstream channel training walls. Channel training walls guide water to and from the powerhouse at this project. This project is the first known use of structural slurry walls as channel training walls at a hydropower project in the United States. The project also included eight 6.3 m (20 ft, 8 in.) long and eight 2.8 m (9 ft, 2 in.) long straight structural slurry wall panels, and four 4.0 m (13 ft) long L-shaped structural slurry wall panels used to enable powerhouse construction. These panels will eventually be incorporated into the outer walls of the powerhouse. There were also 54,311 m² (584,600 ft²) of nonstructural slurry walls constructed to form seepage cutoff walls around the excavation area and below the powerhouse.

The spectral analysis of surface waves (SASW) method is a nonintrusive testing technique for determining shear wave velocity (V_S) profiles of geotechnical sites using seismic interface waves (also called surface waves). Both small-scale and full-scale experiments have been conducted to develop the SASW technique for use underwater. The small-scale tests were performed to validate theoretical predictions regarding dominant types of seismic waves at the water/substrate interface. The tests clearly show a difference between soft and stiff substrates, where the definition of substrate stiffness is based on the value of the velocity of the Rayleigh-type interface wave (V_R) relative to the velocity of compression waves in water (V_W). In the simplest case, where the substrate is soft (V_R<V_W), the dominant wave was found to be the Scholte wave, whose behavior is similar to that of the Rayleigh wave on land. When the substrate is stiff (V_R>V_W), the dominant wave was found to be a generalized Rayleigh wave, the measurement of which is less straightforward. Two full-scale field trials were conducted on soft seafloors: one in the shallow water of a harbor and another as a ship-based experiment at sea. These trials demonstrated that the SASW method is a viable technique for characterizing underwater geotechnical sites, and that it shows promise for further development for remote operation in deep water.

A major issue in the use of geomembranes for waste containment is an estimate of the material's durability (i.e., its lifetime) to various aging phenomena. For high density polyethylene geomembranes, which are the focus of this study, there are three stages in assessing lifetime: depletion of antioxidants, induction time, and time to reach half-life of a relevant engineering property. This paper addresses the first stage of these three sequential processes. Twenty laboratory incubation devices were made to simulate landfill conditions. Four sets of five columns were maintained at elevated temperatures of 85, 75, 65 and 55°C. Samples were retrieved at various intervals over a 24-month incubation period. Various physical, mechanical, and chemical properties were evaluated. The depletion of antioxidants in the incubated samples was monitored using both standard and high pressure oxidative induction time tests. Arrhenius modeling was used on the data to extrapolate the antioxidant lifetime to a typical landfill site temperature of 20°C. The resulting predicted time was 200 to 215 years. Also, it should be emphasized that within this period of time the physical and mechanical properties of the incubated samples remained unchanged.

Pile-supported marine structures are designed for significant amounts of lateral load. In this paper, the influence of parameters like flexural rigidity of pile material, embedment length of pile, and arrangement of piles with respect to the direction of loading on the behavior of laterally loaded pile groups has been studied through an experimental program. The results obtained from lateral load tests carried out on model pile groups arranged at different spacings and embedded in a marine clayey bed are presented and discussed. The results indicate that the lateral load capacity of the pile group depends mainly on the rigidity of pile soil system for different arrangements of piles within a group. This is further substantiated by a simplified finite element analysis bringing in the differences in passive resistance. The group efficiencies under lateral loading obtained from the present investigation are found to be in good agreement with the predictions of earlier researchers.