Journal of Geotechnical and Geoenvironmental Engineering

The evaluation of the drivability of a proposed pipe is a critical task in the planning and execution of pipe-ramming installations, because it results in increased efficiency, safe installations, and significant cost savings. The analysis of drivability provides a means for optimizing the hammer energy required for a given pipe-ramming installation, and it minimizes potential damage to the pipe due to overstressing the pipe material. Four full-scale pipes with diameters ranging from 610 to 3,660 mm installed using pipe-ramming hammers were instrumented to observe the measurement of hammer-pipe energy transfer, driving stresses, and total (static and dynamic) soil resistance to penetration and formed the basis for evaluating drivability. First, the hammer-pipe energy transfer calculated from the observed force and velocity time histories was characterized, indicating the quantity of energy that actually results in the penetration of the pipe through soil. Then, the dynamic model parameters known as the soil quake and damping were back-calculated using common signal-matching analyses and presented as a function of normalized soil resistance. Wave-equation analyses used routinely to assess the constructability of pile foundations were adapted to estimate the observed force time histories and driving curves or the variation of penetration resistance with static soil resistance. Wave-equation analyses were also used to estimate the observed compressive and tensile driving stresses and the accuracy of the estimates characterized. The results of this study and those used to develop equations for static soil resistance to ramming can be used as the basis for the evaluation of the drivability of rammed pipes.

Pipe ramming is a cost-effective trenchless pipe installation method in which percussive blows generated by a pneumatically or hydraulically powered encased piston rammer are used to advance a pipe or culvert through the ground. To evaluate the feasibility of a pipe ramming installation, engineers must be able to reliably predict the pipe drivability and installation stresses. Assessment of the drivability of the pipe and selection of the optimal hammer for pipe ramming installation requires that the static and dynamic soil resistance to ramming at the pipe face and along the casing be reliably estimated. However, pipe ramming-specific models are not currently available, and engineers often resort to the existing traditional pipe-jacking and microtunneling models for static soil resistance computations. This paper describes the results of four full-scale pipes rammed in the field and the corresponding static soil resistance to ramming in granular soils. A companion paper addresses dynamic soil resistance and pipe drivability. The accuracy of the existing pipe jacking and microtunneling-based static soil resistance models is evaluated herein and found to provide unsatisfactory estimates of the face and casing resistance. New semiempirical pipe ramming-specific models are proposed based on the field observations and are found to produce good estimates of static soil resistance for use in pipe drivability evaluations.

This study numerically evaluated the combined effects of different controlling factors (i.e., wall height, stresses induced during backfill compaction, reinforcement stiffness, toe conditions, and facing stiffness) on the behavior of geosynthetic-reinforced soil (GRS) walls under working stress conditions. The results were compared with values predicted by different currently used methods. It was shown that toe resistance has a major effect on the prediction capability of those design methods. Parametric analyses have shown that the amount of tension in the reinforcement varies with restraint at the base of the block facing. For free-base conditions with a constant value for reinforcement stiffness, the tension in the reinforcements was the same irrespective of the facing stiffness and the wall height. For the fixed-base conditions, the amount of tension in the reinforcements and horizontal toe load varied as a function of the facing stiffness. Comparing individual measurements of reinforcement tension verified the significant effect that the toe restraint has on the amount of tension mobilized in the reinforcements at the bottom of the wall. The results showed that the amount of tension in the reinforcement is a function of the magnitude of the compaction-induced stress and the reinforcement stiffness. These results indicate that the compaction-induced stress does not significantly affect the magnitude of the horizontal toe load.

A fully coupled simplified method that incorporates soil nonlinearity is used to conduct sliding-block analysis of slopes subjected to near-fault pulse-like and nonpulse-like ground motions. The effects of the ground motion pulse on the computed sliding displacements are investigated, and the efficiency of various ground motion intensity measures for predicting the sliding displacement of slopes is evaluated. It is shown that the slope is expected to have larger displacements over shorter time intervals when near-fault ground motions have pulse-like characteristics. Results also indicate that for cases in which the natural period of a slope is close to the period of the pulse of a recorded ground motion, an equivalent wavelet pulse appropriately represents the displacement response of slopes. Predictive models are developed for the sliding displacement of near-fault ground motions using spectral acceleration and peak ground velocity as predictive variables. In addition, it is shown that for certain cases displacements can be predicted using simplified pulse parameters and simplified wavelet pulses. The developed models can be incorporated into probabilistic seismic demand analysis for slopes located near active faults.

This paper introduces a novel modular approach for the monitoring of desiccation-induced deterioration in earthen embankments (levees), which are typically used as flood-defense structures. The approach is based on the use of a combination of geotechnical and noninvasive geophysical probes for the continuous monitoring of the water content in the ground. The level of accuracy of the monitoring is adaptable to the available financial resources. The proposed methodology was used and validated on a recently built, 2-km-long river embankment in Galston (Scotland, United Kingdom). A suite of geotechnical probes was installed to monitor the seasonal variation of water content over a 2-year period. Most devices were calibrated in situ. A novel procedure to extrapolate the value of water content from the geotechnical and geophysical probes at any point of the embankment is shown. Desiccation fissuring degrades the resistance of embankments against several failure mechanisms. An index of susceptibility is proposed here. The index is a useful tool to assess the health state of the structure and prioritize remedial interventions.

The liquefaction potential of clean and silty sands is examined on the basis of the field measurement of the shear-wave velocity, $V_s$. The starting point is the database of 225 case histories supporting the Andrus-Stokoe $V_s$-based liquefaction chart for sands, silts, and gravels. Only clean and silty sands with nonplastic fines are considered, resulting in a reduced database of 110 case histories, which are plotted separately by type of deposit. A line of constant cyclic shear strain, ${\gamma }_{cl}\approx 0.03\%$, is recommended for liquefaction evaluation of recent uncompacted clean and silty sand fills and earthquake magnitude, $M_{\mathrm{w}}=7.5$. The geologically recent natural silty sand sites in the Imperial Valley of southern California have significantly higher liquefaction resistance as a result of preshaking caused by the high seismic activity in the valley. A line of constant cyclic shear strain, ${\gamma }_{cl}\approx 0.1–0.2\%$, is recommended for practical use in the Imperial Valley. Additional research including revisiting available $V_s$-based and penetration-based databases is proposed to generalize the results of the paper and develop liquefaction charts that account more realistically for deposit type, seismic history, and geologic age.

An experimental study aimed at providing insights into the effects of the inclination of principal stress directions with respect to the bedding plane and the role of principal stress rotation on the cyclic resistance of sands is presented. A new hollow cylinder torsional shear device commissioned at Carleton University was used to conduct the experiments in water-deposited Fraser River sand. Specimens at identical initial states were subjected to a constant amplitude cyclic shear stress along loading paths that impose different levels of stress rotation. Cyclic resistance decreased significantly as the maximum orientation of the major principal stress increased to approximately 45°–60°, but it increased with further rotation. This is contrary to the conventional idea according to which the weakest response is expected when the loading causes larger principal stress rotation and/or when the major principal stress is aligned with the bedding planes. The alignment of the plane of maximum shear stress toward and stronger time history of shear stress on the horizontal bedding planes lead to increased liquefaction susceptibility. The nature of shear stress on the bedding planes appears more critical than the alignment of the major principal stress along the bedding planes during cyclic loading. Test results also suggest that cyclic simple shear tests on the basis of stress rotation would represent a lower bound or closer to lower bound resistance. Thus, cyclic simple shear tests provide a convenient means of determining the cyclic resistance and the obtained resistance can be considered a conservative measure if field loading conditions deviate from that in simple shear.

In this study, model pile tests were carried out in a custom-made pressurized chamber to explore the mechanisms of a driven pile setup in dry sand. A bender element system and tactile pressure sensors were used in parallel to monitor the stiffness and stress changes in the soil surrounding the pile during the test. The experimental results demonstrate that pile setup is not caused by the increase in at-rest radial stress ${\sigma }_{rp}^{\prime }$. Instead, it is mainly attributed to the increase in radial stress during pile loading $\mathrm{\Delta }{\sigma }_{rp}^{\prime }$, as a result of soil aging (or creep). Pile installation pushes the surrounding soil to the side, thereby imposing additional loading on the soil inside the influence zone. This loading action initiates an associated aging (or creep) process during the setup period; the aging effects ultimately give rise to an increase in both $\mathrm{\Delta }{\sigma }_{rp}^{\prime }$ and pile shaft resistance. The measurements also reveal that the increase in aging-induced soil stiffness is due to contact normal forces among soil particles gradually becoming more homogenized during the setup period. This suggested setup mechanism could explain the absence of pile setup in bored (nondisplacement) piles—the loading action induced by pile installation is too insignificant to trigger the required aging process. Using a similar logic, the mechanism could elucidate why the setup rate is higher in large-displacement piles than in small-displacement piles.

This paper studies the effect of electromagnetic (EM) waves—with minimal heat generation—on transport mechanisms to improve soil/groundwater cleanup. This effect was experimentally examined for the transport of a nonreactive dye in water. The setup was tested at frequencies between 50 and 200 MHz. EM waves’ electric field component was numerically simulated and then validated against an experimentally measured electric field. Dielectrophoretic forces were then computed by using the simulated electric field data. The dye flow was observed to be in the same direction as the numerically simulated, dielectrophoretic forces. Recorded temperature variations within the medium showed similar trends ($<1°\mathrm{C}$ increase during EM stimulation) for all frequencies; however, only at the specific frequencies of 65 and 75 MHz was the dye flow controlled by EM waves. This observation suggests that EM waves—and not thermal effects—controlled the dye transport.

A 5.35 m high test embankment was constructed on a soft foundation improved by geotextile-encased granular columns (GECs). The embankment construction was performed in four stages over 65 days, resulting in a total applied stress of around 150 kPa. The soft soil and the encased columns were instrumented to measure surface settlements, excess pore pressure, surface vertical stresses, and radial deformation of the geotextile encasement. Stress concentration and the difference in settlement between the top of the encased columns and the soft soil were studied. Results showed that the differential settlement increased as the embankment height increased and when the excess pore pressure was being dissipated. Due to soil arching, the vertical stress supported by the encased column was over two times greater than the stress transmitted to the soft soil. Also, vertical stress on the encased column increased as consolidation progressed, whereas it did not vary significantly on the soft soil.

Shallow penetrometers—such as the hemiball and toroid—were conceived as potential in situ testing devices with the ability to measure: (1) soil strength parameters during vertical penetration, (2) soil consolidation characteristics during dissipation tests postpenetration, and (3) interface friction during torsional loading. Knowledge of the response of soil to such tests is critical to the design of subsea pipelines and the ability to measure the response of soil to all three types of test using a single device in situ from a mobile testing platform, such as a remotely operated vehicle (ROV), would be highly advantageous. Potential benefits of the employment of such devices could include significant time and cost savings and improved spatial measurement density, since more tests could be conducted along the route of a pipeline if an ROV is used as a mobile in situ testing platform. This paper presents an assessment of the ability of the hemiball and toroid to measure soil strength parameters directly from their response to vertical penetration. A large deformation finite-element approach was employed to model the penetration process and initial simulations were validated against small-strain analyses published in the literature. A comprehensive parametric study was then conducted investigating the impact on normalized penetration resistance of soil unit weight, shear strength gradient and penetrometer-soil interface friction. A forward model was derived from the parametric analyses and its inverse performance (i.e., the ability to infer soil parameters from force-displacement response) was assessed using additional large deformation analyses with randomly assigned material parameters within realistic bounds. Both variants of shallow penetrometer investigated are found to be well suited to inferring soil strength parameters directly from their response to vertical penetration.

Geotechnical centrifuge tests can provide valuable insights into the mechanisms governing the performance of buildings affected by liquefaction. An area particularly lacking knowledge is the effect of liquefaction on adjacent structures, which is a common possibility in urban areas. Two well-instrumented centrifuge tests were performed to investigate the response of isolated and adjacent structures founded on ground that underwent varying degrees of liquefaction. Three types of single-degree-of-freedom model structures were used in the experiments. Acceleration, pore water pressure, and settlement measurements illustrated that liquefaction-induced settlement of structures depends on a complex interaction of ground motion, soil, and structural characteristics. For the cases examined in this study, adjacent structures experienced moderately lower foundation accelerations than isolated structures of the same type. Adjacent structures tended to tilt away from one another and settled less than isolated structures. The physical restraint imposed by an adjacent foundation limited lateral soil movement and reduced the total settlement of the neighboring structure.

This study proposes a simplified reliability-based design (RBD) method for the serviceability limit state (SLS) of excavations considering cross walls. Although the effects of cross walls are highlighted, the proposed method is applicable to cases without cross walls. In the proposed RBD method, partial factors are calibrated using rigorous reliability theory to meet the target reliability index. A design example is used to illustrate the use of calibrated partial factors and to demonstrate the effectiveness of cross walls.

The cone penetration test (CPT) was evaluated as a tool for characterizing landfilled municipal solid waste (MSW). Cone penetration test soundings were performed at 16 locations in a closed MSW landfill in Florida, United States, where tip resistance ($q_t$), sleeve friction resistance ($f_s$), and friction ratio ($f_r$) data were collected up to a depth of 10 m, and compared to waste properties from borings in the same location as five of the CPTs. The delineation of cover soil, waste, and subgrade soil was readily identifiable from the CPT data, but intermediate cover layers could not be discerned. At greater depths in the landfill, waste generally exhibited greater degradation with an average biochemical methane potential of $0.044\mathrm{L}{\mathrm{CH}}_4/\mathrm{g}$ volatile solids versus shallower waste that was less degraded with an average BMP of $0.200\mathrm{L}{\mathrm{CH}}_4/\mathrm{g}$ volatile solids. More degraded waste tended to have lower tip resistances of 3.6–3.7 MPa than less degraded waste that exhibited 5.0–5.4 MPa. The friction ratio tended to be greater for more degraded waste (2.8–3.2%) than less degraded waste (2.3–2.4%). The CPT data collected from the MSW landfill were also compared to conventional correlations to soil classification systems. The CPT data for more degraded waste generally correlated with finer soil classifications while CPT readings of less degraded waste corresponded to more coarse soils.