Journal of Geotechnical and Geoenvironmental Engineering

Earth embankment dams are one of the most commonly constructed hydraulic infrastructures worldwide. One mode of dam failure is piping through the embankment, which is initiated by internal erosion of soil particles inside dams. In this study, the applicability of microbially induced carbonate precipitation (MICP) for internal erosion control is examined in the laboratory using sand-kaolin mixtures of different particle sizes. A series of internal erosion tests are conducted using a newly designed rigid-wall column erosion test apparatus, which allows independent control of MICP treatment. Erosion rate/coefficient, volumetric change, and permeability are characterized during the internal erosion process. It is found that MICP treatment facilitates the reduction of erosion and volumetric contraction of sand-clay mixtures investigated in the current study. Carbonate precipitation increases the erosion resistance of sand-clay mixtures by absorbing/coating fine particles directly and bridging the contacts of coarse particles. An improved effectiveness of internal erosion control is observed in the sand-clay mixture having a higher gap ratio. This observation is due to the inherently large porosity, which hosts more carbonate precipitation. The difficulty of bacteria and chemical injection in sand-clay mixtures triggers the flushing of produced calcium carbonate, which reduces the overall carbonate content and MICP treatment efficiency. The spatial distribution of precipitation within the soil is also altered.

The compressibility of municipal solid waste (MSW) is of engineering interest as it affects the short-term and long-term performance of landfills, as well as their expansion, closure, and postclosure development. An assessment of the field settlement behavior of MSW can be reliably executed only when the various mechanisms contributing to the settlement are properly taken into account. A comprehensive large-size experimental testing program that involved a total of 143 one-dimensional compression tests from five landfills, in Arizona, California, Michigan, and Texas of the United States as well as Greece was executed to systematically assess the compressibility characteristics of MSW subjected to a compressive load. Emphasis is given to the influence of waste structure, waste composition, unit weight, and confining stress on the compressibility parameters that are used in engineering practice, such as the constrained modulus and compression ratio, as well as long-term compression ratio due to mechanical creep only. The effect of waste composition and unit weight on the compressibility parameters is quantified. It is also found that the type of waste constituent (i.e., paper, plastic, or wood), as well as the waste’s anisotropic structure can have an effect on the compressibility characteristics of soil-waste mixtures. The proposed relationships can be used to estimate compressibility parameters of MSW at any degradation state as long as the waste composition and unit weight are known.

In order to better understand the response of driven, closed-ended, pipe piles subjected to axial loads and examine the performance of existing pile design methods, static and dynamic load tests were performed on a closed-ended steel pipe pile driven in a multilayered soil profile. The test pile was fully instrumented with electrical-resistance and vibrating-wire strain gauges, which enabled the determination of residual loads before sensors were reset and load-transfer curves for all loads applied at the pile head during the static load test. The ultimate base and limit shaft resistances of the test pile measured in the static load test and estimated from dynamic load tests are compared with estimates made using several cone penetration test-based (CPT-based) and property-based pile design methods. Two additional case histories are used to verify these design methods, most of which produce satisfactory estimates of pile resistance.

This study presents an enhanced hydraulic fixed-piston (HNS-N) sampler that reflects a local practice. This sampler was employed at a deltaic site along with two other types of samplers: a similar hydraulic (HNS-K) type with no vacuum breaker and an oil-operated (ONS) sampler that is equipped with a vacuum breaker and is fixed at the center of a casing. The generation of a slowly but erratically increasing pressure in the hydraulic samplers often does not ensure constant speed and full penetration; thus, the pressure in these samplers was increased rapidly after the drill rods were filled with water. By contrast, the pressure in the ONS sampler was increased instantaneously. The hydraulic samplers exhibited slightly discrete penetration behavior, whereas the ONS sampler induced constant penetration. The sample qualities of the samplers are ordered based on an evaluation via two nondestructive methods and a consolidation test, as follows: $\mathrm{ONS}\mathrm{>}\mathrm{HNS}–\mathrm{N}\mathrm{>}\mathrm{HNS}–\mathrm{K}$. The sample quality was affected significantly by the uniformity of penetration behavior and slightly by the penetration rate (mostly $6.4–10.7\mathrm{cm}/\mathrm{s}$). In addition, sample quality was strongly influenced by the use of the vacuum breaker.

A split Hopkinson pressure bar (SHPB) was used to characterize the propagation of high intensity large strain compressional waves through cemented paste backfill (CPB). The effects of curing age, cement content, and degree of saturation on stress refraction at interfaces, velocity of propagation, and internal damping in CPB were investigated. The results show that a smaller portion of the incident stress wave is refracted at the CPB interface in unsaturated specimens in comparison to those in a near fully saturated condition. Increased refraction ratios and velocities of propagation as a result of increased curing age and cement content were mainly observed in unsaturated specimens. In addition, the effects of degree of saturation on stress wave propagation in unsaturated material seemed negligible. The compression wave propagation velocity in the SHPB was also compared with small strain velocities found by means of ultrasonic wave measurements. The measured small strain wave velocities were found to be consistently smaller than the large strain velocities found in the SHPB. Similarly, the small strain elastic theory was found to underpredict the transmission ratios at CPB interfaces. Thus, it was proposed to account for correction factors by accounting for the changes in density and constrained modulus under high amplitude and short duration compressive waves. The coefficient of attenuation remained practically unchanged at different curing ages and was shown to significantly decrease near saturation.

This study evaluates granular liquefaction triggering case-history data using a nonparametric approach. This approach assumes no functional form in the relationship between liquefied and nonliquefied cases as measured using cone penetration test (CPT) data. From a statistical perspective, this allows for an estimate of the threshold of liquefaction triggering unbiased by prior functional forms, and also provides a platform for testing existing published methods for accuracy and precision. The resulting threshold exhibits some unique trends, which are then interpreted based on postliquefaction deformation behavior. The range of postliquefaction deformations are differentiated into three zones: (1) large deformations associated with metastable conditions; (2) medium deformations associated with cyclic strain failure; and (3) small deformations associated with cyclic stress failure. Deformations are further defined based on the absence or presence of static driving shear stresses. This work presents a single simplified framework that provides quantitative guidance on triggering and qualitative guidance on deformation potential for quick assessment of risks associated with seismic soil liquefaction failure.

Live poles have been used to stabilize shallow slopes. Most of the existing work has focused on pole reinforcement. The effects of pole transpiration on slope stability are unclear. This study aims to investigate the effects of pole transpiration on rainfall-induced slope hydrology through centrifuge model tests. A novel live-pole modeling technique using real branch cuttings was adopted to simulate the hydrological effects of the transpiration-induced suction in the centrifuge. Suction responses during rainfall were recorded and back-analyzed by seepage analysis. Higher suction was preserved after rainfall when pole transpiration induced higher suction before rainfall. This is because inducing higher suction would lower the soil water storage capacity and hydraulic conductivity. After a rainfall event with a return period of 20 years, up to 10 kPa of suction was preserved in the pole-supported slope to provide stabilization effects.

A total of 123 measured maximum nail-load data were collected from instrumented soil nail walls reported in the literature. Filtered data sets corresponding to short-term and long-term measurements were used to evaluate the accuracy of the current Federal Highway Administration (FHWA) simplified method to calculate maximum nail loads under operational conditions. The accuracy of load predictions was quantified by the mean and coefficient of variation (COV) of the ratio (bias) of measured load to predicted load. Data in short-term and long-term categories were also investigated according to frictional-cohesive and frictional soil types. Based on the available data, the current FHWA simplified method was found to overestimate both long-term and short-term maximum nail loads on average. The spreads in prediction accuracy measured by the COV of bias were 38 and 52% for long-term and short-term data, respectively. Large spreads in prediction accuracy were also found using data for walls with cohesive-frictional soils alone. With the exception of the frictional soil data set, there was an undesirable correlation (dependency) between method accuracy and predicted maximum nail load using the current FHWA simplified method. A modified FHWA simplified method equation is proposed that has fewer empirical coefficients than the current formulation (i.e., three compared to five) and is shown to be more accurate on average and to have less spread in prediction accuracy for all data sets. Furthermore, hidden dependencies between method accuracy and magnitude of predicted load are not present.

Long-term ground movements occur after tunnel construction in clayey soils due to dissipation of excess pore pressure generated during construction and a new seepage state that depends on the drainage conditions of the tunnel. A methodology was proposed in the past to evaluate the long-term surface settlements for tunnels in London clay. This paper extends the previous work by proposing a new method to estimate both consolidation-induced vertical and horizontal displacements, as well as consolidation-induced peak horizontal strains. In this method, a new relative soil-lining permeability index, which was modified from the earlier work, is proposed by assuming a radial seepage flow into a tunnel. Using this index along with tunnel geometry and soil properties, a series of equations was derived to better facilitate the calculation of the long-term ground displacements and strains compared to the normalized charts adopted in the previous evaluation method. The applicability of the proposed method is tested against two case histories in London.

Compacted clay liners are vulnerable to desiccation cracking if exposed to atmospheric conditions for extended periods of time. Three clayey soils typically used as landfill liners were studied in relatively large-scale containers exposed to real atmospheric conditions for a full annual cycle. Desiccation cracking and particularly the variation in depth of cracks were examined in soil pairs; one set was directly exposed to atmospheric conditions and the other covered with a white separator geotextile. Cracks started to grow deeper in time with some variations with rainfall events up to a few months followed by no significant increase later. Smaller crack depths were observed for the soil with the lowest plasticity index. Using a geotextile cover resulted in 35–79% reduction in average crack depth. Hydraulic conductivity of the soils increased at the end of the experiment with greater increase for soils with deeper cracks.

In this paper, a new method is proposed for analyzing laterally loaded rock-socketed shafts by extending the elastoplastic continuum method developed by the corresponding author and his colleagues. The method considers a nonuniform shaft with diameter and/or flexural rigidity changing with depth and embedded in multiple layers of soil/rock masses. The method considers not only the yielding of the soil/rock mass but also the decrease in flexural rigidity of the shaft due to cracking. The proposed method is verified by applying it to analyze instrumented laterally loaded tests on rock-socketed drilled shafts at two different sites and comparing the analysis results with field test data. The results indicate the importance of considering the decrease in flexural rigidity of the shaft due to cracking, and show the simplicity and reliability of the proposed method.

The installation sequence and spacing of displacement piles can influence the driving resistance (i.e., blow count) and associated capacity, however, engineers can rarely account for this effect in a direct manner. Increasing the availability of high-quality measurements of the effects of driving sequence and spacing to designers could help improve the understanding of production data and inform decisions mid-project. This paper presents some observations of pile driving resistance and pile capacity measured following an experimental program on the use of timber displacement piles in a well-characterized test site. Significant increases in pile capacity were observed as a function of decreased pile spacing depending on the order of installation. After correcting for the estimated residual loads, a fourfold difference in shaft capacity was observed between free-field and a pile in-filled at five pile head diameters.