Journal of Geotechnical and Geoenvironmental Engineering

Surface fault rupture during recent earthquakes has significantly damaged structures. Although several researchers have studied surface fault rupture, the effects of fault rupture propagating through soil that has been ruptured previously have not been investigated. Yet, faults rupture multiple times so that native soil deposits will have likely undergone previous ruptures that would have developed shear bands within the soil, and the stress state of the soil will have evolved because of these events. In addition, the predominant modes of soil shearing during the fault rupture process have not been characterized fully. Numerical simulations are performed to analyze the mechanics of dip-slip surface fault rupture and to explore the effects of previously ruptured soil. The numerical results demonstrate that the soil rupture process occurs in two distinct stages. First, broad deformation occurs before strain localization, which is followed by more localized deformation after shear band formation. Stress paths in the rupture zone are analogous to plane-strain extension (loading) and plane-strain compression (unloading) element tests for reverse and normal faults, respectively. The performance of structures significantly depends on whether the soil has been ruptured previously.

The potential for the desiccation of a geosynthetic clay liner (GCL) forming part of a single composite landfill liner is evaluated. A thermohydromechanical model is used to identify conditions likely to cause desiccation. Simulations for typical landfill conditions show that the potential risk of desiccation exists even at relatively low temperatures (i.e., 35°C). It is found that the water content of the GCL prior to waste placement, the liner temperature, the overburden stress, the grain size and water content of the subsoil, and the depth to aquifer all affect the potential for desiccation. The results suggest that the placement of GCLs directly over coarse-grained soils or drainage layers should be evaluated carefully. This study highlights the need for more research into the potential for GCL desiccation and, in particular, the need to establish water retention curves for different GCLs over a range of stresses and degrees of hydration before heating, so that the effect of stress and hysteresis on the potential for desiccation can be examined. The findings of this study are limited by the approximations and assumptions described in the paper and, even then, apply only to the GCL and conditions examined. Changing the assumptions may change the findings. The findings should not be generalized to other composite liners without independent verification. The results serve to identify some of the situations that may lead to GCL desiccation, and it is hoped that they will prompt more research on this important topic.

The effectiveness of chemical stabilization and its permanency were investigated by subjecting chemically treated soils to leaching tests by internal water flushing, which simulates moisture ingress/digress into subsoils from rainfall events. Control and chemically stabilized soils from eight different locations were subjected to these leaching tests over 14 cycles in the laboratory. Each leaching cycle represents one pore volume of water flushed through the soil specimen. Leaching samples were collected after 3, 5, 7, and 14 cycles and were chemically analyzed to address pore fluid chemical composition changes and possible leaching of the chemical additives. Unconfined compressive strength tests were conducted on soil specimens after 3, 7, and 14 leaching cycles to study soil strength variations. The effects of soil type, stabilizer type and dosages, and the curing method on the leaching of stabilizers are analyzed. Test results and analyses indicate that leaching of stabilizer did occur, but the amounts are too low to induce strength losses in the soils analyzed. Also, approximate correlations are developed between leaching cycles and field precipitation and moisture infiltration processes to determine the number of years replicated in the field.

The legal limitations on the amount of biodegradable municipal solid waste (MSW) disposed of to landfill have led to the development of a range of pretreatment processes known generically as mechanical biological treatment (MBT). This paper presents the results of a detailed study of the degradation and settlement characteristics of two such MBT waste residues. The effects of mechanical creep and biodegradation are quantified separately, and compared with each other and with those for raw (untreated) MSW. The effects of different degrees of treatment prior to landfilling are considered in the context of the relationship between biodegradation and settlement. The results are discussed with reference to uncoupled models for estimating consolidation, creep, and biodegradation-induced settlements in MBT wastes. The methods for determining appropriate parameter values and applying these models to practice are also suggested.

In the design of piled raft foundations, the control of total and differential settlements is crucial. On the basis of centrifuge tests, this study presents the feasibility of a fairly optimal pile arrangement scheme for reducing total and differential settlements. Two models of piled raft foundations having the same flexible raft and number of piles, the uniform pile arrangement model and the concentrated pile arrangement model, and one model having a rigid raft with a concentrated pile arrangement were designed for centrifuge tests. The settlements of three rafts of the piled raft models and the induced bending moments of two flexible rafts were measured during the load application process. The measured results were compared between the tests to illustrate the ability of the concentrated pile arrangement scheme in reducing total and differential settlements, as well as induced bending moment. Moreover, three piled rafts were simulated by the Plaxis 3D Foundation software package to calculate the total and differential settlement, as well as the induced bending moments, after which a comparison was made with the centrifuge tests to verify the reliability of these tests. The results show that the piled raft model with a concentrated pile arrangement can effectively decrease the total and differential settlements in comparison with the pile raft model with a uniform pile arrangement.

The objective of this paper is to document and study the failure of a driven, steel pipe pile foundation system supporting an offshore platform. The three-pile system failed in overturning because of a pull-out failure of the most critically loaded pile in a hurricane 5 years after installation. The calculated tensile capacity of this pile using the American Petroleum Institute (API) design method is close to the estimated load at failure. This case history is significant because it represents the failure of a large-diameter pile in service when loaded by a storm. Also, this case history generally affirms the current design methods and contradicts a widely held perception that offshore pile designs are significantly conservative. This case history highlights the opportunities to improve design practice by explicitly accounting for pile flexibility when dealing with strain-softening soils and by considering the capacity of the foundation system as well as the capacity of individual piles in design.

The undrained strengths and friction angles of a variety of natural fine-grained soils are investigated over an effective stress range of 0.1 to 10 MPa. The resedimentation technique was used to produce identical saturated samples for laboratory shear testing. The majority of the results presented are derived from $K_o$-consolidated undrained triaxial compression tests, although behavior under direct simple shear and triaxial extension modes of shear is also presented for a single soil. Normalized shear stress-strain responses, undrained strength ratios, and critical state friction angles are found to vary considerably and consistently at each overconsolidation ratio when viewed over a significant effective stress range. Correlations are developed that allow the undrained strength and friction angle of a fine-grained soil, as well as the variation in these properties with stress level, to be estimated effectively from liquid limit, together with an evaluation of the in situ stress history of the sediment. Liquid limit is an easily measured index property that reflects the clay mineralogy and clay fraction of a soil.

This paper presents an experimental study of tool wear and abrasivity of granular soils using a testing system specifically designed for the evaluation of wear on earth-moving machines, especially soft ground tunneling applications where the impact of soil abrasion on the operation is significant. In the testing system, a propeller fitted with steel covers of different hardnesses is rotated at 60 rpm in granular soil samples in a chamber under ambient pressures of up to 10 bar. The developed system can quantitatively assess the abrasive characteristics of soils through the measurement of weight loss on the special covers of the propeller, accounting for soil gradation, mineral composition, sphericity and roundness, water content, and tool hardness. Preliminary test results indicate that water content, particle angularity, and relative hardness between the tool and soil have significant impact on tool wear and soil abrasion. For the tests conducted, it is observed that angular sands produce significantly higher tool wear than round sands in dry condition. Tool wear first increases with water content until the water content reaches approximately 7–10%; beyond this range, higher water content reduces tool wear. An increase in hardness ratio (tool/mineral), corresponding to an increase in tool hardness and/or a decrease in mineral hardness, results in a decrease in tool wear in dry sand mixtures, but this trend is not monotonic for sand mixtures with high water content.

The effects of the frequency of cyclic shearing and vertical consolidation stress on the cyclic degradation and cyclic pore water pressure in normally-consolidated kaolinite clay having $\text{PI}=28$ were investigated with the help of the cyclic strain-controlled Norwegian Geotechnical Institute (NGI) simple shear test. The testing program encompassed three cyclic shear strain amplitudes, ${\gamma }_c=0.1,0.25,\text{and}\hspace{0.17em}0.5\%$, two vertical effective consolidation stresses, ${\sigma }_{\mathit{vc}}^{\prime }=220\hspace{0.17em}\text{and}\hspace{0.17em}680\hspace{0.17em}\text{kPa}$, and three frequencies, $f=0.001,0.01,\text{and}\hspace{0.17em}0.1\hspace{0.17em}\text{Hz}$. The results reveal that the cyclic degradation parameter, $t$, which measures the rate of cyclic degradation with the number of cycles, increases substantially with $f$ and decreases with ${\sigma }_{\mathit{vc}}^{\prime }$. If $f$ is increased 10 times, $t$ may increase by 20–50%. If ${\sigma }_{\mathit{vc}}^{\prime }$ is increased from 220 to 680 kPa, the $t$ parameter may decrease by 20–38%. The cyclic pore water pressure normalized by ${\sigma }_{\mathit{vc}}^{\prime }$ decreases with $f$ and ${\sigma }_{\mathit{vc}}^{\prime }$.

Evidence of the lateral compression of the Earth’s crust is apparent from folds and faults observed in rock, and the mechanics describing their development is well established in the fields of structural geology and tectonics. This paper describes similar structures in soils that developed in multilayered varved clay under the side slopes and toe of an embankment due to the nonuniform loading. Using analytical methods derived for the buckling of thin plates of alternating high and low moduli, predictions of wavelengths and the critical stresses to initiate folding were determined, and found to correlate with field and laboratory measurements. When these conditions occur, the resulting fabric changes have implications for slope stability modeling and the interpretation of field monitoring observations. This includes the ability of the clay to sustain large strains as it transitions from a highly anisotropic macrofabric to a relatively homogeneous material, without undergoing shear failure.

This paper presents a numerical and experimental investigation on the effects of pore structures on the static mechanical properties of porous sandstone. Three-dimensional (3D) numerical models of porous sandstone with different statistical pore parameters are constructed using a software program and the experimentally acquired data of the parameters. The mechanical properties of sandstone are numerically tested using Brazilian disc split tests to probe the influences of pore structures. A number of physical models having similar statistical characteristics of pores and physical properties with those of the numerical models are produced using modeling materials. Brazilian disc tests and computer tomography tests are performed on the physical specimens with different porosities to clarify the responses of pore structures during failure processes. The numerical analysis implies that pores significantly affect the mechanical properties of porous sandstone such as stress concentration, distribution, and the connection of the failed material elements. It is shown that the statistical distribution of pore radii presents a certain degree of influence on the split failure behavior of porous rock, which is closely related to rock porosity. However, distribution of spatial location of pores has negligible influence on stress distribution, failure mechanisms, and the split tensile strength of the porous media. A porosity of 15% seems to be a threshold porosity, above which the effects of geometrical and statistical characteristics of pore structures on the split mechanical properties of porous rock become significant. The laboratory test verifies that the developed physical models have consistent geometric and statistical characteristics of pores with those of the real sandstone. The measured split mechanical properties of the physical models present good agreement with the predictions of numerical simulations.

Rock mass structures are key factors that control and influence the stability of foundation engineering, underground engineering, and slope engineering. Based on the traditional plane block theory, a new approach of three-dimensional (3D) surface block identification and analysis is put forward. The 3D rock mass model integrated geological structures with stochastic rock structural network planes were first built according to the given mathematical definition of surface blocks. Then, subject to the four principles of closure, completeness, uniqueness, and validity, the proposed method can search, identify, and analyze key free blocks and constraint blocks. This approach was applied to study the rock blocks of a developed hydropower project and offers a new measure for rock mass stability analysis and control.

This paper presents experimental data obtained by long-term monitoring of the strains occurring in several segments of a precast RC segmental lining adopted to support a bored tunnel. Careful and tight control of the strains was also carried out during the early installation stages, which only lasted a few hours. The strains were measured using vibrating wire gauges embedded in the segments during construction at the manufacturer’s plant. The measurements were recorded using a wireless data logger, which allowed accurate follow up of the strain changes in the segments beginning with the concreting stage and for a long time after the tunnel construction. With reference to the various construction stages, the measured strains are presented and discussed. Their maximum values are just a few hundred microstrains, making the thermal effects on the gauge readings significant. For this reason the problem of their elimination is briefly addressed in the paper. The process used to derive the internal forces in the lining is not at all straightforward and the paper describes the process and reports the obtained internal forces both in short- and long-term conditions.

Uniaxial tension experiments on precracked rocklike samples and the related numerical simulations using FRANC3D were performed to investigate the growth mechanism of three-dimensional (3D) cracks in rocks under tension as well as the strength and failure behavior of samples. Experimental results indicate that the geometric characteristics of preexisting cracks, including crack dip angle, crack spacing, and crack intensity, have significant effects on the strength and failure modes of the samples. Failure of samples resulted from the propagation of a single crack and the coalescence of multiple cracks if the spacing between adjacent cracks is less than the length of the cracks. Distribution of mixed-mode stress-intensity factors (SIFs) and energy-release rates (ERRs) along the fronts of cracks with different geometric characteristics was investigated numerically, and the results can provide an interpretation for the experimental results. Based on numerical simulations of the propagation processes of single and two parallel cracks, the growth patterns and growth rates of 3D cracks were studied. The simulation results of crack growth correspond well with the experimental phenomena.

Strong ground motions from the $M_w=6.6$ 2007 Niigata-ken Chuetsu-oki earthquake were recorded by a free-field downhole array at a nuclear power plant. Site conditions consist of about 70 m of medium-dense sands overlying clayey bedrock, with groundwater located at 45 m. Ground shaking at the bedrock level had a geometric mean peak acceleration of 0.55g, which reduced to 0.4g at the ground surface, indicating nonlinear site response. One-dimensional ground response analysis of relatively weak motion aftershock data provides good matches of the observed resonant site frequencies and amplification levels, provided small-strain damping levels somewhat larger than those from laboratory tests are applied. Nonlinear ground response analyses of strong-motion data using laboratory-based modulus reduction and damping relations valid up to moderate strain levels ($<\mathrm{\sim 0.5}\%$) produce unrealistic strain localization at a velocity contrast. A procedure is presented to more realistically represent the large-strain portion of backbone curves by asymptotically approaching the shear strength at large strains, which removes strain localization for this application and provides reasonable matches of observed and computed ground motions.

A feasibility study was performed on using xanthan gum and guar gum, two biopolymers that are naturally occurring and inexpensive, to stabilize mine tailings (MT). The simple fall cone method was adopted to evaluate the liquid limit and undrained shear strength of sun-dried MT mixed with xanthan gum or guar gum solutions at different concentrations. Environmental scanning electron microscopy (ESEM) imaging was also conducted to study the microstructure of the biopolymer-MT system. The results indicate that the inclusion of xanthan gum or guar gum increases both the liquid limit and the undrained shear strength of the MT, higher biopolymer concentrations leading to greater increases. The increase of the liquid limit and undrained shear strength of the MT mixed with a biopolymer solution is mainly attributable to the high viscosity of the biopolymer pore fluid and the bonding between the biopolymer and the MT particles. Guar gum is more effective than xanthan gum in increasing the liquid limit and undrained shear strength of the MT, because the guar gum solution is more viscous than the xanthan gum solution at the same concentration, the guar gum–MT particle bonding is stronger than the xanthan gum–MT particle bonding, and guar gum causes a lower degree of aggregation of MT particles than xanthan gum. By comparing the undrained shear strength data with empirical equations in the literature, two new equations were proposed for predicting the undrained shear strength of the MT mixed with a biopolymer for water contents near the liquid limit, based on the liquid limit and water content, and the liquidity index, respectively.

In 1986–1989, Jackson Lake Dam, Wyoming, was removed after standard penetration tests indicated that the foundation soil was subject to liquefaction. Part of a subsequent research program involved measuring lateral in situ stresses at various depths in the foundation soil by use of the ${\mathrm{K}}_{\mathrm{o}}$ Stepped Blade, a device that introduces a stepwise lateral displacement of soil so contact pressures can be extrapolated to give the hypothetical pressure on a zero-thickness step. The foundation soil was cohesionless mix of alluvial and deltaic silts and sands with some sharp-edged gravel. The lateral stress measurements established relationships between the four topics in the title of this paper. A normal consolidation state, meaning that a soil is in equilibrium with its own weight, can be established when ${\mathrm{K}}_{\mathrm{o}}$ is constant with depth and lateral effective stresses extrapolate to zero at the ground surface. On this basis, three stress zones were identified: (1) Based on limited data, an uppermost zone, to a depth of 4 m (13 ft) underneath the dam, was identified as being normally consolidated under the weight of the dam. This is as expected and probably occurred during construction. Underneath the upper zone was (2) a transition zone, 4 to 5.5 m (13 to18 ft) in depth, and under that (3) a lower zone, 5.5 to 10 m (18 to 33 ft) in depth. The lower zone was determined to be normally consolidated without the weight of the dam. ${\mathrm{K}}_{\mathrm{o}}$ without the weight from the dam was determined to be 0.5, and lateral effective stresses extrapolate to zero at the predam ground surface. Note that the value of ${\mathrm{K}}_{\mathrm{o}}$ was measured and not derived from empirical correlations. Nevertheless, it is consistent with normal consolidation and a friction angle of 30 degrees reported for this deposit. Despite having been characterized as cohesionless, the soil deep underneath the dam had resisted consolidation for over 60 years, and the depth to the underconsolidated layer is consistent with observations that liquefaction can be deep-seated. The existence of such a layer calls into question the use of a temporary surcharge for site preparation for cohesionless soils, or a reliance on measurements that settlement has stopped. A similar situation can be anticipated under existing structures such as dams and highway embankments that are located on the geologically young but historically old granular soil deposits of floodplains and deltas. The weight of the dam reduced ${\mathrm{K}}_{\mathrm{o}}$ in the lower zone soil from 0.5 to 0.35. This can happen only if the soil has developed sufficient strength to resist consolidation and can be attributed to aging. Mohr circles drawn from the lateral stress measurements indicate a gain in cohesion of the order of 34 kPa (4.9 psi or 700 psf) from aging. The gain also may be explained by an increase in the friction angle from dilatancy attributed to cementation rims at grain contacts. The site was treated by deep dynamic compaction that increased ${\mathrm{K}}_{\mathrm{o}}$ to 1.0, but with considerable variability. That value indicates a temporary liquid condition, and may have been preserved by seepage forces when pore water pressure supported the entire weight of the soil column. The replacement dam reduced the average ${\mathrm{K}}_{\mathrm{o}}$ from 1.0 to about 0.5, which should be sufficient prevent future liquefaction. However, the cap on ${\mathrm{K}}_{\mathrm{o}}$ of 1.0 during ramming can restrict the amount of additional load if the final ${\mathrm{K}}_{\mathrm{o}}$ is to be no lower than the normal consolidation value.

A new definition of the factor of safety—the vector-sum factor of safety (VFOS) considering force-vector characteristics—is introduced and is defined as the ratio of projection of the resistance force to that of shear force in the potential sliding direction of the slope. This study develops a new analysis method for solving the VFOS of slope with a noncircular slip surface considering interslice forces based on slice method. The analysis method developed for slope stability is implemented in the spreadsheet software Microsoft Excel for efficient calculation. The proposed method is verified through comparison with the VFOS by the FEM and the rigorous limit-equilibrium method, and the significance of the proposed method is highlighted.

The effects of pore water chemistry on the cyclic behavior of fine-grained soil were examined by performing undrained cyclic ring-shear tests on a natural soil treated with solutions of sulfuric acid (${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$), sodium hydroxide (NaOH), and sodium chloride (NaCl). In addition, different amounts of the chemicals were used to clarify the influence that ion concentrations in the pore fluid can have on the cyclic shear strength of soil. The results of laboratory tests indicated that cyclic shear strength was sensitive to changes in the pore fluid composition, and changes in cyclic behavior of soil became more pronounced as the concentration of each chemical increased.

On December 13, 1990, a moderate earthquake ($M_L=5.4$ and MKS intensity equal to VII) struck the southern part of eastern Sicily causing intense damage in some localized areas and the loss of 19 human lives. At Augusta, which has soft-soil conditions, amplification phenomena were observed, and RC frame buildings based on piles were severely damaged. Because seismic regulations were not enforced in the area during construction, the buildings were designed only for static loads. An investigation was conducted on the superstructures, soil, and piled foundations for evaluating the potential to repair and retrofit these buildings. The site has been subjected to extensive soil investigations. Loading tests on single piles and a three-pile group were conducted to test the integrity of the piles after the seismic event. To simulate the behavior of piles subjected to both inertial and kinematic effects resulting from the earthquake, a pseudostatic pushover analysis was carried out. Seismic loading was evaluated by a deterministic approach based on accelerograms measured during the earthquake. Because the load-bearing capacity of the existing foundation was insufficient to resist the design seismic loading, retrofitting of the piled foundation required the enlargement of the foundation and new bored piles.

The Kozeny-Carman (K-C) equation can be used to predict the saturated hydraulic conductivity of a soil, provided enough information is given regarding the porosity and the specific surface. The main limitation of the K-C equation lays in the determination of the specific surface of the soil, a parameter that is not regularly measured but can be estimated with analytical or empirical relations. A method to evaluate the soil’s specific surface is proposed, which combines the contribution of the plastic clayey fraction and that of the granular silty-sandy particles. The applicability of the proposed method and its effect on the performance of the K-C equation have been verified by comparing the K-C estimated hydraulic conductivity with the result of approximately 130 hydraulic conductivity tests on saturated soil specimens in the triaxial apparatus. The results show that the K-C equation and the method for estimating the specific surface predict within an order of magnitude the saturated hydraulic conductivity of clayey to silty-sandy soils with measured hydraulic conductivity in the range $1\times {10}^{-11}–5\times {10}^{-6}\hspace{0.17em}\text{m/s}$.