Showing papers in "Journal of Geotechnical and Geoenvironmental Engineering in 2013"

Experimental Optimization of Microbial-Induced Carbonate Precipitation for Soil Improvement

Abstract: Implementation of laboratory-tested biomediated soil improvement techniques in the field depends on upscaling the primary processes and controlling their rates. Microbial-induced carbonate precipitation (MICP) holds the potential for increasing the shear stiffness and reducing the hydraulic conductivity by harnessing a natural microbiological process that precipitates calcium carbonate. The study presented herein focuses on controlling MICP treatment of one-dimensional flow, half-meter-scale column experiments. Treatment was optimized by varying procedural parameters in five pairs of experiments including flow rates, flow direction, and formulations of biological and chemical amendments. Monitoring of column experiments included spatial and temporal measurements of the physical, chemical, and biological properties essential to the performance of MICP, including shear wave velocity, permeability, calcium carbonate content, aqueous calcium, aqueous ammonium, aqueous urea, and bacterial density. Rela...

Shear-Wave Velocity–Based Probabilistic and Deterministic Assessment of Seismic Soil Liquefaction Potential

Abstract: Shear-wave velocity (Vs) offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property. This paper presents the results of an 11-year international project to gather new Vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence. Toward that objective, shear-wave velocity test sites were identified, and measurements made for 301 new liquefaction field case histories in China, Japan, Taiwan, Greece, and the United States over a decade. The majority of these new case histories reoccupy those previously investigated by penetration testing. These new data are combined with previously published case histories to build a global catalog of 422 case histories of Vs liquefaction performance. Bayesian regression and structural reliability methods facilitate a probabilistic treatment of the Vs catalog for performance-based engineering applications. Where possible, uncertainties of the variables comprising both the seismic demand an...

Generalized Approach for Prediction of Jet Grout Column Diameter

Abstract: This paper presents a generalized approach for predicting the diameter of jet grout columns based on the theoretical framework of turbulent kinematic flow and soil erosion. The proposed calculation method is applicable to all conventional jet-grouting systems and takes into account the full range of operational parameters, fluid properties, soil strength, and particle size distribution, including the effect of the injection time on erosion distance. It was demonstrated that the increase in the jet grout column diameter arising from the use of a compressed air shroud in the double and triple fluid systems is approximately 27–81% for the typical range of air pressure of 0.5–1.5 MPa. The proposed method was applied to four case histories involving four variants of jet-grouting systems, i.e., single fluid, double fluid, triple fluid, and an enhanced triple fluid system. Comparison between the calculated and the measured jet grout column diameters indicated that the proposed method can produce reasonab...

Analysis of an Image-Based Method to Quantify the Size and Shape of Sand Particles

Abstract: Sand response depends on particle morphology (size and shape). In geotechnical research and practice, size is typically assessed by sieve analysis and particle shapes are qualitatively described. Technological developments mean that digital images of sand particles can easily be obtained, enabling shape to be quantified. The complexity associated with many digital image analysis algorithms seems to have restricted their use to fundamental research studies. This study introduces a pragmatic approach for quantitative shape analysis that has the potential to be broadly adopted in geotechnical engineering research and practice. The approach generates three shape measures (convexity, sphericity, and aspect ratio) that can easily be calculated from digital images. Following an analysis of these shape measures and the imaging method used here, a database of 36 sands, including many of the sands commonly used in geotechnical research, is presented. The subjective nature of qualitative description is clear...

Critical Hydraulic Gradients of Internal Erosion under Complex Stress States

Abstract: Internal erosion involves selective loss of fine particles within the matrix of coarse soil particles under seepage flow, which affects the hydraulic and mechanical behavior of the soil. In this research, extensive laboratory internal erosion tests were conducted under complex stress states following three stress paths: isotropic, drained triaxial compression, and triaxial extension stress paths. These tests were designed to investigate the initiation and development of internal erosion and the effect of stress state on critical hydraulic gradients. The entire erosion process can be divided into four phases: stable, initiation, development, and failure. Accordingly, three critical gradients termed as initiation, skeleton-deformation, and failure hydraulic gradients, can be defined. These critical gradients correspond to the onset of erosion of the fine particles filling the large pores of the skeleton, the buckling of the strong force chains formed by the coarse particles, and the soil failure, re...

Geotechnical Tests of Sands Following Bioinduced Calcite Precipitation Catalyzed by Indigenous Bacteria

Abstract: Recentexperimentshaveshownthatexogenousbacteriacanbeintroducedintosoilforthepurposeofinducingcalciteprecipitation. A series of tests are documented in this paper that demonstrate that natural indigenous bacteria can also be stimulated to induce calcite precip- itation with measurable changes in geotechnical properties. Tests reported in this paper include a microcosm experiment with cone-penetration testing and cyclic triaxial shear tests. These experiments demonstrate that indigenous bacteria can induce significant quantities of calcite pre- cipitation, that calcite precipitation can result in measurable changes to geotechnical soil properties, and that the cyclic resistance ratio can be increased substantially with moderate levels of calcite precipitation. Using indigenous bacteria to modify soil properties is a significant step in making biomodification of soils economically viable. DOI: 10.1061/(ASCE)GT.1943-5606.0000781. © 2013 American Society of Civil Engineers. CE Database subject headings: Biological processes; Soil liquefaction; Cement; Bacteria; Soil stabilization; Earthquake. Author keywords: Biological processes; Liquefaction; Cementation; Bacteria; Calcite; Stabilization; Earthquake; Soil improvement.

Bayesian Approach for Probabilistic Site Characterization Using Cone Penetration Tests

Abstract: This paper develops a Bayesian approach for probabilistic site characterization (i.e., on both stratigraphy and soil properties) using cone penetration tests (CPTs). The available site information prior to the project (e.g., existing geological maps, geotechnical reports, and local experience) is used in the Bayesian approach as prior knowledge, and it is integrated systematically with results of CPTs that are performed deliberately for the project. The inherent spatial variability of soil is modeled explicitly by random field theory. The proposed approach contains two major components: a Bayesian model class selection method to identify the most probable number of statistically homogenous layers of soil and a Bayesian system identification method to estimate the most probable layer thicknesses and soil properties probabilistically. Equations are derived for the Bayesian approach, and the proposed approach is illustrated using a set of real CPT data obtained from a site in Netherlands. It has been...

Stiffness of clays and silts: Normalizing shear modulus and shear strain

Abstract: An analysis is presented of a database of 67 tests on 21 clays and silts of undrained shear stress-strain data of fine-grained soils Normalizations of secant G in terms of initial mean effective stress p′ (ie, G/p′ versus log γ) or undrained shear strength cu (ie, G/cu versus log γ) are shown to be much less successful in reducing the scatter between different clays than the approach that uses the maximum shear modulus, Gmax, a technique still not universally adopted by geotechnical researchers and constitutive modelers Analysis of semiempirical expressions for Gmax is presented and a simple expression that uses only a void-ratio function and a confining-stress function is proposed This is shown to be superior to a Hardin-style equation, and the void ratio function is demonstrated as an alternative to an overconsolidation ratio (OCR) function To derive correlations that offer reliable estimates of secant stiffness at any required magnitude of working strain, secant shear modulus G is norma

Improving mechanical properties of sand using biopolymers

Abstract: Natural polymers (biopolymers) are discussed as environmentally friendly and sustainable grouting chemicals. This paper presents guidelines for selecting potentially useful biopolymers for strengthening cohesionless soil. Agar and six modified starches were identified for further study over a range of concentrations (1–4% agar and 0.5–1% starch). Experimental results demonstrated the compatibility of agar and starch. Depending on the biopolymer concentration, the unconfined compressive strength of the sand treated with agar and starch biopolymers ranged from 158 to 487 kPa. Triaxial compression tests over a range of confining pressures also indicated that the biopolymers effectively increased the cohesion intercept and stiffness of the treated sand.

Long-Term Lateral Cyclic Response of Suction Caisson Foundations in Sand

Abstract: Skirted gravity base foundations and suction caisson foundations are considered as viable alternatives to monopile foundations for offshore wind turbines. While recent work has focused on the monotonic moment-rotation response for shallow foundations, the cyclic response and the accumulation of rotation over the life of the turbine must also be addressed. This paper presents cyclic loading tests where approximately 10,000 cycles, with different loading characteristics, were applied to a model shallow foundation (a caisson) in loose sand. On the basis of these tests, a framework for assessing the accumulated angular rotation because of cycling was developed. The settlement and cyclic stiffness response of the caisson were also assessed. It was found, not unexpectedly, that the accumulated settlement of the caisson increased with the number of cycles and cyclic amplitude. It was also found that a cyclic loading regime intermediate between one-way and full two-way cycling produced the largest rotatio...

Stress-Strain Degradation Response of Railway Ballast Stabilized with Geosynthetics

Abstract: Large cyclic loading on ballasted railroad tracks is now inevitable owing to an increased demand for freight and public transport. This leads to a progressive deterioration and densification of railroad ballast and consequently to the loss of track geometry and differential settlement. Understanding these complex stress-strain and degradation mechanisms is essential to predict the desirable track maintenance cycle, as well as the design of new track. This paper presents the results of cyclic drained tests and numerical studies carried out on a segment of model railway track supported on geosynthetically reinforced railroad ballast bed. The relative performance and effectiveness of single- and dual-layer configurations of geosynthetic reinforcement was evaluated using a large-scale prismoidal triaxial chamber. Laboratory tests on unreinforced and reinforced railway track were simulated in a numerical model, and the results were then analyzed to better understand the distribution of displacements and stresses inside the railroad ballast layer. It was observed that in view of strain and breakage control, both the type of reinforcement and its layout played a vital role in improving the capacity of the track. These laboratory test findings were supported by the predictions from an advanced elastoplastic numerical analysis.

Characteristics of a Large-Scale Deep Foundation Pit Excavated by the Central-Island Technique in Shanghai Soft Clay. I: Bottom-Up Construction of the Central Cylindrical Shaft

Abstract: A large amount of field and experimental data has been devoted to rectangular excavations thus far. In contrast, very few data were available for cylindrical excavations, especially those with large diameters in thick soft clay deposits. Via a comprehensive instrumentation program on a 100-m-wide×25.89-m-deep unpropped (self-supported) cylindrical excavation constructed by the bottom-up method in Shanghai soft clay, the characteristics of this large-sized circular excavation were extensively investigated. This cylindrical shaft was a part of a large-scale deep foundation pit excavated by the central-island technique. The investigated items included (1) lateral wall deflections, (2) vertical wall movements, (3) lateral ground movements, (4) ground settlements, (5) subsurface settlements, (6) basal heaves, (7) vertical column movements, (8) column stresses, and (9) variation of pore pressures along depth and artesian water levels. Analysis of the field data indicates that discharging of the deep art...

Unconfined Compression Strength of Reinforced Clays with Carpet Waste Fibers

Abstract: This paper presents results of a comprehensive investigation on the utilization of carpet waste fibers in reinforcement of clay soils. Effects of adding proportionate quantities of two different types of shredded carpet waste fibers to clay soils (i.e., 1, 3, and 5% by dry weight of the soil) were investigated and evaluated. The investigation was conducted on specimens prepared at their maximum dry unit weight and optimum moisture content, as well on specimens prepared at variable conditions of dry unit weight and moisture content. A comparison was also made on specimens prepared at the same fiber content by changing dry unit weight while moisture content was kept unchanged or by changing both dry unit weight and moisture content. The investigation revealed that inclusion of carpet waste fibers into clay soils prepared at the same dry unit weight can significantly enhance the unconfined compression strength (UCS), reduce postpeak strength loss, and change the failure behavior from brittle to ductile. The results also showed that the relative benefit of fibers to increase the UCS of the clay soils is highly dependent on initial dry unit weight and moisture content of the soil. Failure patterns were gradually transformed from the apparent classical failure for unreinforced soil specimens to barrel-shaped failures for reinforced specimens at 5% fiber content.

Bayesian Updating of Soil Parameters for Braced Excavations Using Field Observations

Abstract: A Bayesian framework using field observations for back-analysis and updating of soil parameters in a multistage braced excavation is presented. Because of the uncertainties originating from...

Applicability of Enzymatic Calcium Carbonate Precipitation as a Soil-Strengthening Technique

Abstract: A grouting technique for enzymatic calcite precipitation is evaluated. Urea and calcium salt, at various concentrations, are mixed with a concentration-fixed enzyme to obtain the optimal precipitation of CaCO3. The optimally combined solution is injected into sand samples in small PVC cylinders. Then, the improvement in small-scale samples is observed. The combination, approved for small-scale tests, is further used for larger-scale tests. The porosity distribution within the soil is evaluated by sampling the treated sand at different locations. A precipitation ratio up to 80% can be obtained using a small amount of the enzyme. The results show that the in situ enzymatic CaCO3 precipitation technique may be feasible for use in larger-scale applications. A multiphysics simulator that considers the calcite precipitation reaction during the transport of the solution is adopted to predict the evolution of the porosity. The predicted porosities are compared with the measured porosities. The results sho...

Characteristics of a Large-Scale Deep Foundation Pit Excavated by the Central-Island Technique in Shanghai Soft Clay. II: Top-Down Construction of the Peripheral Rectangular Pit

Abstract: Because of its large size (30,000 m2 in plan), the 17.85- to 25.89-m-deep foundation pit of the 492-m-high Shanghai World Finance Center building was excavated by the central-island technique, i.e., bottom-up construction of the central cylindrical shaft first and then top-down construction of the peripheral rectangular pit. As part of the comprehensive study on the characteristics of this large-scale foundation pit, this study mainly focuses on the behaviors of the peripheral pit via the following investigated items: (1) lateral wall deflections; (2) vertical wall movements; (3) lateral ground movements; (4) axial forces in the cast floor slabs and braced struts; (5) lateral earth pressures on both sides of retaining walls; (6) variation of pore pressures along depth and deep artesian water levels; (7) ground settlements; (8) subsurface settlements; (9) basal heaves; (10) vertical column movements; and (11) column stresses. To explore the potential effects of pit sizes on the excavation behaviors...

Role of Particle Angularity on the Mechanical Behavior of Granular Mixtures

Abstract: Particle shape affects the mechanical behavior of soils, including packing density, stiffness, volume change during shear, and strength. Laboratory experiments conducted to study the mechanical response of sand mixtures made of round and angular grains show an increase in void ratio, small strain shear modulus Gmax (constant fabric), oedometric compressibility CC (fabric changes), and friction angle but a decrease in lateral stress coefficient k0 as the mass fraction of angular particles increases. These results reflect variations in particle mobility and highlight the relative role of contact stiffness versus fabric changes.

Effects of Geocell Confinement on Strength and Deformation Behavior of Gravel

Abstract: In past years, railroad transportation has been of growing interest because of its efficiency and advancement in railway technologies. However, many issues arise because of the variability in subsurface conditions along the sizeable lengths of track that exist. One very important issue is the need for significant upkeep and maintenance for railways passing over areas of poor soil conditions as a result of continuous deformation and a lack of stiffness from the foundation. One general solution for lack of substructure integrity has been confinement, applied through a variety of reinforcement types, including geocell. To investigate the effectiveness of geocell confinement on substructure integrity, a series of embankment model tests with different configurations of geocell placement (one layer and two layers of geocell) were constructed and loaded monotonically and cyclically for comparison with unreinforced, control tests. On the completion of these tests, the model embankments were simulated nume...

Biopolymer Stabilization of Mine Tailings

Abstract: 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 u...

Application of the Kriging-Based Response Surface Method to the System Reliability of Soil Slopes

Abstract: Response surface methods (RSMs) are attractive approaches for slope reliability analysis because such methods can integrate deterministic numerical slope stability evaluation and reliability analysis. For a slope in layered soils, its performance function is generally nonlinear and the system failure probability could be larger than the failure probability of the most critical slip surface. In this study, the applicability of the kriging-based RSM for system reliability of soil slopes is assessed through its application to two slopes with obvious system effects. It is found that the kriging method combined with Monte Carlo simulation (MCS) can deliver accurate system failure probability estimation. For comparison, the classical RSM based on the iterative local approximation of the performance function may fail to detect the most critical slip surface. The classical RSM can only calculate the failure probability of one slip surface even if the first-order reliability method or MCS is used. Even whe...

Elastic and Large-Strain Nonlinear Seismic Site Response from Analysis of Vertical Array Recordings

Abstract: Strong ground motions from the Mw=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 (<∼0.5%) produce unrealistic strain localization at a velocity contrast. A procedure is presented to more realistically represent the large-strain por...

Effects of Particle Size Distribution on Shear Strength of Accumulation Soil

Abstract: This paper focuses on the effects of particle size distribution on shear strength of accumulation soil. A series of direct shear box tests and triaxial tests were performed to characterize the shear strength of the accumulation soil. Results from the direct shear tests indicate that the range of the angle of shearing resistance of the accumulation soil is 33.5–54.6°, and those from the triaxial tests indicate that the angle is 37.2–50.7°. The basic properties of the soil, such as median particle diameter, coefficient of uniformity, and gravel content, were used to analyze the effects. The angle of shearing resistance is generally increasing with increasing median particle diameter and gravel content and decreasing with increasing coefficient of uniformity.

Deformation of Coal Fouled Ballast Stabilized with Geogrid under Cyclic Load

Abstract: This paper presents the results of laboratory investigations into the deformation of coal fouled ballast stabilized with geogrid at various degrees of fouling. A novel track process simulation apparatus was used to simulate realistic rail track conditions subjected to cyclic loading, and the void contamination index (VCI) was used to evaluate the level of ballast fouling. The experimental results show that coal fines act as a lubricant, causing grains of ballast to displace and rotate, and as a result, accelerate its deformation. However, coal fines also reduce ballast breakage because of a cushioning effect, that is, by reducing interparticle attrition. The inclusion of geogrid at the interface between the layer of ballast and subballast provides additional internal confinement and particle interlocking via geogrid apertures, which reduces deformation. A threshold value of VCI=40% is proposed to assist practitioners for conducting track maintenance. If the level of fouling exceeds this threshold,...

Numerical Solution of Stone Column–Improved Soft Soil Considering Arching, Clogging, and Smear Effects

Abstract: Improvement of soft clay deposits by the installation of stone columns is one of the most popular techniques followed worldwide. The stone columns not only act as reinforcing material increasing the overall strength and stiffness of the compressible soft soil, but they also promote consolidation through effective drainage. The analytical and numerical solutions available for ascertaining the response of column-reinforced soil have been developed on the basis of the equal strain hypothesis. For typical surcharge (embankment) loading, the free strain analysis appears to give more realistic results comparable to field data. The paper presents a novel numerical model (finite-difference method) to analyze the response of stone column–reinforced soft soil under embankment loading, adopting the free strain approach and considering both arching and clogging effects. Apart from predicting the dissipation of excess pore water pressure and the resulting consolidation settlement with time, the load transfer m...

Liquefaction Response of Partially Saturated Sands. I: Experimental Results

Abstract: The liquefaction response of partially saturated loose sandswas experimentally investigatedto assess theeffect of partial saturation on thegenerationof excessporewater pressures.Anexperimental setup includingacyclicsimpleshearliquefaction boxwas devisedandman- ufactured.Theboxincludesporepressureanddisplacementtransducersaswellasbenderelementsandbendingdiskstomonitortheresponseof partially saturated specimens. Uniform partially saturated specimens with controlled density and degree of saturation were prepared by wet pluviationofpowderedsodiumperboratemonohydratemixedwithOttawasand.Thereactionofthesodiumperboratewithporewaterreleased minute oxygen bubbles, thus reducing the degree of saturation of the specimens. The uniformity of a specimen was confirmed with S wave velocity measurements and a high-resolution digital camera. The P wave velocity measurements could only confirm the presence of partial saturation but not the degree of saturation. Partially saturated specimens with varying relative densities and degrees of saturation when tested under a range of cyclic shear strains do not achieve initial liquefaction defined by maximum pore pressure ratio (ru,max) being 1.0. For a given degree of saturation and cyclic shear strain amplitude, the larger the relative density, the smaller is ru,max. For a given degree of saturation and relative density, the larger the shear strain amplitude, the larger is ru,max. The excess pore pressure ratio (ru) can be significantly smaller than ru,max depending on the number of cycles of shear strain. Tests on the sustainability of partial saturation under upward flow gradient and base excitation led to the conclusion that the specimens remained partially saturated without significant change in the degree of saturation. Based on the experimental test results presented in this paper, an empirical model for the prediction of ru in partially saturated sands under earthquake excitation is presented in a companion paper. DOI: 10.1061/(ASCE)GT.1943-5606.0000815. © 2013 American Society of Civil Engineers. CE Database subject headings: Soil liquefaction; Soil treatment; Saturated soils; Sand (soil type); Pore pressure; Cyclic tests; Entrainment; Bubbles; Experimentation. Authorkeywords:Soilliquefaction;Soiltreatment;Saturation;Porepressure;Cyclictests;Entrainment;Bubbles;Inducedpartialsaturation; Liquefaction mitigation; Bender elements; Bending disks.

One-Way Cyclic Triaxial Behavior of Saturated Clay: Comparison between Constant and Variable Confining Pressure

Abstract: The one-way cyclic triaxial test has been recognized as a useful tool for solving many engineering problems, such as the prediction of deformation in subsoils under traffic loading. Most st...

Field Tests, Modification, and Application of Deep Soil Mixing Method in Soft Clay

Abstract: The installation of soil-cement columns causes excess pore-water pressures and movements of surrounding ground, which affect adjacent underground structures. In Shanghai, a triple-shaft deep soil mixing (DSM) method has been proposed and is widely used to minimize the installation effects. However, when this DSM method was used to install soil-cement columns close to a Metro tunnel, unacceptable soil displacement was caused, even at the very beginning. Therefore, it was decided to conduct field tests to investigate the effect of major factors affecting DSM installations and then modify the construction parameters so that the soil displacement caused by DSM construction would not exceed the allowable limit. The field tests consisted of two phases: Phase I tests of single DSM column installations close to the Metro tunnel to modify the construction parameters, and Phase II tests of continuous multiple DSM column installations far from the Metro tunnel to validate the modified construction parameters...

Strength of High Water-Content Marine Clay Stabilized by Low Amount of Cement

Abstract: An ideal solution for disposal of large volumes of unwanted dredged clays is to stabilize and use them as fill materials for land reclamations. This kind of stabilized dredged fill (SDF) requires a lower cement amount (Cm) compared with traditional cement-treated soils. Strength behavior might be different for mixes within the inactive zone (lower Cm) and those within the active zone (higher Cm). The SDF is fully/partially within the inactive zone. A new set of unconfined compressive strength (qu) data as well as qu data compiled from literature covering both lower and higher Cm are analyzed. First, main parameters governing qu of cement-stabilized clays are identified: (1) cement amount (Cm), and (2) water content (W). Then, qu behaviors in the inactive zone and active zone are compared. Results indicate that a nonlinear normalized qu-Cm trend is commonly observed in the inactive zone whereas a linear one is observed in the active zone. In both zones, the normalized qu-W curve (or normalized qm-C...

Noncoaxial Behavior of Sand under Various Stress Paths

Abstract: In this paper, the results of three series of drained tests carried out on sands using hollow cylinder apparatus are presented. The noncoaxiality, defined as the difference between the major principal stress direction and the corresponding principal strain increment direction, is investigated. In the first series of tests, the sand was isotropically consolidated before being sheared with the fixed principal stress direction. In the other two series of tests, the sand specimens were isotropically consolidated and then sheared by rotating the major principal stress axes while the deviator stress level was either fixed (pure stress rotation) or increased continuously (combined shear loading). The experimental results provide clear evidence for material noncoaxiality when the rotation of principal stress direction is involved. The results from these series of tests show that the degree of noncoaxiality depends on the level of deviatoric stress and the stress increment direction. It tends to decrease w...

Estimating the Rate of Erosion of a Silty Sand Treated with Lignosulfonate

Abstract: This paper describes a theoretical model to capture the rate of erosion of a silty sand based on the principle of conservation of energy. Erosion is considered to begin when the interparticle bonds between grains are broken by hydrodynamic stresses exerted on the soil particles. These detached particles are then suspended and transported by the flow of eroding fluid. It is further assumed that once the particles are fully suspended and have reached the flow velocity, resettlement does not take place. Stabilization of soil particles because of lignosulfonate (LS) treatment is represented by the increased strain energy required to break the interparticle bonds. The equation proposed in this study is based on the shear stress-strain characteristics, mean flow velocity, mean particle diameter, and the packing arrangement of particles. The result of the proposed study is presented in the form of erosion rate versus the hydraulic shear stress. The model is validated with a series of laboratory erosion t...