Showing papers in "Journal of Geotechnical and Geoenvironmental Engineering in 2008"

Assessing the Potential of Internal Instability and Suffusion in Embankment Dams and Their Foundations

Abstract: Suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces. Soils susceptible to suffusion are described as internally unstable. This technical note describes a method for assessing the potential of internal instability of silt-sand-gravel or clay-silt-sand-gravel soils based on their particle size distribution based on laboratory tests carried out by the writers and results published by others. It is shown that some commonly used methods are conservative for these soils.

Empirical Predictive Models for Earthquake-Induced Sliding Displacements of Slopes

Abstract: Earthquake-induced sliding displacement is the parameter most often used to assess the seismic stability of slopes The expected displacement can be predicted as a function of the characteristics of the slope (yield acceleration) and the ground motion (eg, peak ground acceleration), yet there is significant aleatory variability associated with the displacement prediction Using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction Empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2,000 acceleration–time histories and four values of yield acceleration These empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement, with the goal of minimizing the standard deviation of the displacement prediction The combination of peak ground acceleration and peak ground velocity is the tw

Experimental Parametric Study of Suffusion and Backward Erosion

Abstract: Within hydraulic earth structures (dikes, levees, or dams), internal seepage flows can generate the entrainment of the soil grains. Grain transportation affects both particle size distributions and porosity, and changes the mechanical and hydraulic characteristics of the earth's structure. The occurrence of failures in new earth structures due to internal erosion demonstrates the urgency of improving our knowledge of these phenomena of erosion. With this intention, a new experimental device has been developed that can apply hydraulic stresses to reconstituted consolidated cohesive soils without cracks in order to characterize the erosion evolution processes that might be present. A parametric study was conducted to examine the influence of three critical parameters on clay and sand erosion mechanisms. When the hydraulic gradient was low, it was concluded that the erosion of the structure's clay fraction was due to suffusion. When the hydraulic gradient increased, it was concluded that the sand fraction erosion initiation was due to backward erosion. The extent of the erosion was dependent on the clay content. The study underlines the complexity of confinement stress effects on both erosion phenomena.

Capacity, Settlement, and Energy Dissipation of Shallow Footings Subjected to Rocking

Abstract: The effectiveness of structural fuse mechanisms used to improve the performance of buildings during seismic loading depends on their capacity, ductility, energy dissipation, isolation, and self-centering characteristics. Although rocking shallow footings could also be designed to possess many of these desirable characteristics, current civil engineering practice often avoids nonlinear behavior of soil in design, due to the lack of confidence and knowledge about cyclic rocking. Several centrifuge experiments were conducted to study the rocking behavior of shallow footings, supported by sand and clay soil stratums, during slow lateral cyclic loading and dynamic shaking. The ratio of the footing area to the footing contact area required to support the applied vertical loads (A∕ Ac ) , related to the factor of safety with respect to vertical loading, is correlated with moment capacity, energy dissipation, and permanent settlement measured in centrifuge and 1 g model tests. Results show that a footing with lar...

Characterization of Cemented Sand by Experimental and Numerical Investigations

Abstract: In this study, the effects of cementation on the stress–dilatancy and strength of cemented sand are investigated through experimental characterizations using triaxial tests and numerical simulations using the discrete element method. At small strains, dilatancy is hindered by the intact bonding network that produces a web-patterned force chain. After yielding, the increase in the dilatancy accelerates. Two competing but intimately related processes determine the peak strength: Bond breakages cause a strength reduction but the associated dilatancy leads to a strength increase. This finding and the experimental observation that the dilatancy at the peak state increases with increasing cement content explain why the measured peak-state strength parameters, c′ and ϕp′ , are relevant to the cement content. With increasing strain, the force-chain distribution gradually changes to a thick columnar shape, which mostly appears inside the shear band. At the ultimate state, the cementing bonds remain to form cluster...

Pore Pressure Generation Models for Sands and Silty Soils Subjected to Cyclic Loading

Abstract: This paper discusses the applicability of two simple models for predicting pore water pressure generation in nonplastic silty soil during cyclic loading. The first model was developed by Seed et al. in the 1970s and relates the pore pressure generated to the cycle ratio, which is the ratio of the number of applied cycles of loading to the number of cycles required to cause liquefaction. The second model is the Green-Mitchell-Polito model proposed by Green et al. in 2000, which relates pore pressure generation to the energy dissipated within the soil. Based upon the results of approximately 150 cyclic triaxial tests, the writers show that both models are applicable to silty soils. A nonlinear mixed effects model was used for regression analyses to develop correlations for the necessary calibration parameters. The results show that the trends in both α and pseudoenergy capacity calibration parameters for the Seed et al. and Green et al. pore pressure generation models, respectively, differ significantly for...

Simplified Plane-Strain Modeling of Stone-Column Reinforced Ground

Abstract: The acceleration of consolidation rate by stone columns was mostly analyzed within the framework of a basic unit cell (i.e., a cylindrical soil body around a column). A method of converting the axisymmetric unit cell into the equivalent plane-strain model would be required for two-dimensional numerical modeling of multicolumn field applications. This paper proposes two simplified conversion methods to obtain the equivalent plane-strain model of the unit cell, and investigates their applicability to multicolumn reinforced ground. In the first conversion method, the soil permeability is matched according to an analytical equation, whereas in the second method, the column width is matched based on the equivalence of column area. The validity of these methods is tested by comparison with the numerical results of unit-cell simulations and with the field data from an embankment case history. The results show that for the case of linear-elastic material modeling, both methods produce reasonably accurate long-term consolidation settlements, whereas for the case of elastoplastic material modeling, the second method is preferable as the first one gives erroneously lower long-term settlements.

Analysis of Factors Influencing Soil Classification Using Normalized Piezocone Tip Resistance and Pore Pressure Parameters

Abstract: This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance ( qt ) and penetration pore-water pressure at the shoulder ( u2 ) . Parametric studies for normalized cone tip resistance (Q= qcnet ∕ σ v0 ′ ) and normalized excess pressures (Δ u2 ∕ σ v0 ′ ) as a function of overconsolidation ratio (OCR= σ vy ′ ∕ σ v0 ′ ) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter ( Bq =Δ u2 ∕ qcnet ) . The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q–Δ u2 ∕ σ v0 ′ space is superior to Q– Bq space when...

Overview of New Orleans Levee Failures: Lessons Learned and Their Impact on National Levee Design and Assessment

Abstract: This paper provides an overview of the Southeast Louisiana Flood and Hurricane Protection System that was in place at the time of Hurricane Katrina. Both geography and components of the system are described. A brief description of the development of the storm, the major damage caused, and lessons learned are discussed.

Deep Mixing Induced Property Changes in Surrounding Sensitive Marine Clays

Abstract: This paper presents a field study of installation effects of deep mixed columns on properties of the sensitive Ariake marine clay. Cone penetration tests were performed in the field to evaluate the change in the strength of the surrounding clay with time. Soil samples were taken before and after column installation to evaluate variations of physical, mechanical, and chemical properties of the surrounding clay. Test results indicated that the water content of the surrounding clay decreased while the concentration of cations increased as sampling locations approached the columns. Shear strength of the surrounding clay decreased during the installation but recovered after a short period of curing. Shear strength continued to increase with time over a period of 70 days. Based on the regression results, the surrounding soil after the installation of the columns took approximately 10 days to recover to the strength value before installation. On average, the shear strength of the surrounding clay increased over the original strength by approximately 23% after 40 days and 50% after 70 days, respectively. Discussion is presented on strength changes and key influence factors including soil disturbance and fracturing, thixotropy, consolidation, and diffusion of cations from deep mixed columns to the surrounding clay.

Uplift Mechanisms of Pipes Buried in Sand

Abstract: Reliable design against upheaval buckling of offshore pipelines requires the uplift response to be predicted. This paper describes a model-scale investigation into the mechanisms by which uplift resistance is mobilized in silica sand, and illustrates how the observed mechanisms are captured in prediction models. A novel image-based deformation measurement technique has been used. The results show that peak uplift resistance is mobilized through the formation of an inverted trapezoidal block, bounded by a pair of distributed shear zones. The inclination of the shear zone is dependent on the soil density, and therefore dilatancy. After peak resistance, shear bands form and softening behavior is observed. At large pipe displacements, either a combination of a vertical sliding block mechanism and a flow-around mechanism near the pipe or a localized flow-around mechanism without surface heave is observed, depending on the soil density and particle size.

Probabilistic Seismic Hazard Analysis for the Sliding Displacement of Slopes: Scalar and Vector Approaches

Abstract: Sliding block displacements often are used to evaluate the potential for ground failure due to slope instability. The procedures used to assess sliding block displacement typically use deterministic or pseudoprobabilistic approaches, in which the uncertainties in the expected ground motion and resulting displacement are either ignored or not treated in a rigorous manner. Thus, there is no concept of the actual hazard associated with the computed displacement. This paper presents a fully probabilistic framework for assessing sliding block displacements. The product of this analysis is a displacement hazard curve, which provides the annual rate of exceedance, λ, for a range of displacement levels. The framework considers two procedures that will yield a displacement hazard curve: (1) a scalar hazard approach that utilizes a single ground motion parameter and its associated hazard curve to compute permanent displacements; and (2) a vector hazard approach that predicts displacements based on two (or more) ground motion parameters and the correlation between these parameters. The vector approach reduces the displacement hazard significantly, as compared with the scalar approach, because of the reduction in the variability in the displacement prediction. Comparison of the fully probabilistic approach with an approach using probabilistically derived ground motions reveals that using a ground motion for a given hazard level does not produce a displacement level with the same hazard.

Behavior of Railroad Ballast under Monotonic and Cyclic Loading

Abstract: A relatively new method for mechanized maintenance of railroad ballast (stoneblowing) puts a layer of single size stone between the ballast and each tie creating a two-layer gravel support. To get a better understanding of the behavior of this arrangement series of large diameter, triaxial tests have been carried out on single size and layered specimens. A new method of quantifying particle breakage during testing has been developed, and a conceptual model used to explain the combined effects of shearing and breakage on observed specimen behavior.

Soil Vibrations Caused by Underground Moving Trains

Abstract: The wave propagation problems caused by the underground moving trains are analyzed by the 2.5-dimensional finite/infinite-element approach. The near field of the half-space, including the tunnel and parts of the soil, is simulated by finite elements, and the far field extending to infinity by infinite elements. The train is simulated as a sequence of wheel loads moving at constant speeds. Using the present approach, a two-dimensional profile with three degrees per node is used to simulate the three-dimensional behavior of the half-space, which is valid for the case when the material and geometry of the system are invariant along the tunnel direction. The factors considered in the analysis of ground-borne vibrations include the damping ratio and stratum depth of the supporting soils, the depth and thickness of the tunnel, and the moving speed and excitation frequency of the trains. It was found that moving train loads with nonzero excitation frequencies can induce significantly higher vibrations than the static moving loads. The effect of stratum depth depends highly on the excitation frequency. For a tunnel constructed in a stiffer soil, the ground surface vibrations can be greatly reduced. Other conclusions useful to practical engineers are contained in the parametric study.

Case Histories in Soil and Rock Erosion: Woodrow Wilson Bridge, Brazos River Meander, Normandy Cliffs, and New Orleans Levees

Abstract: This lecture presents four case history examples of erosion processes. Because the topic of soil and rock erosion is relatively underdeveloped in geotechnical engineering, an introduction precedes the case histories to describe some fundamental aspects of erosion. Erosion involves the soil or rock through its erodibility, the water through its velocity, and the geometry of the obstacle through its size and shape. Knowledge of these three components is needed for any erosion problem to be studied and solved. A set of fundamental issues are addressed in the first part including an erodibility classification for soils and rocks, an explanation of the stresses imposed by the water on the soil-water or rock-water interface, and an explanation of how the geometry impacts the problem. The Woodrow Wilson Bridge case history outlines a new and less conservative method to compute the scour depth and gives examples of bridge scour calculations. The Brazos River meander case history outlines a new method to predict m...

Geological and Physical Factors Affecting the Friction Angle of Compacted Sands

Abstract: This study evaluated the effects of physical characteristics and geologic factors on the shear strength of compacted sands from Wisconsin that are used as granular backfill for mechanically stabilized earth walls and reinforced soil slopes. Physical properties and shear strength were determined for 30 compacted sands collected from a broad range of geological deposits. Relationships between strength/deformation behavior, geologic origin, and physical properties were used to categorize the sands into four friction angle groups. Sands with the lowest friction angle are derived from weathering of underlying sandstones, and tend to be medium-fine, well-rounded, and poorly graded sands. Sands with the highest friction angle are from recent glacial activity and tend to be coarser grained, well-graded, and/or angular sands. A multivariate regression model was developed that can be used to predict friction angle ( ϕ′ ) of compacted sands from comparable geological origins based on effective particle size ( D10 ) ...

Levee Erosion by Overtopping in New Orleans during the Katrina Hurricane

Abstract: Erodibility of a soil is defined here as the relationship between the erosion rate of a soil dz/dt and the velocity v of the water flowing over it, or the relationship between the erosion rate of a soil dz/dt and the shear stress developed by the water at the water-soil interface. This is called the erosion function. The test used to measure the erosion function of the levee soils is the erosion function apparatus test. The test consists of eroding a soil sample by pushing it out of a thin wall steel tube and recording the erosion rate for a given velocity of the water flowing over it. Several velocities are used and the erosion function is defined. A new erosion category chart is proposed to reduce the erodibility of a soil or rock to a single category number. Twenty three samples were retrieved from 11 locations at the surface of the levees around New Orleans. Thirteen were samples from Shelby tubes while ten were bag samples. The results obtained show a large variation of erosion resistance among the soils tested. Some of the levees associated with the location of the samples resisted the overtopping erosion very well; others eroded completely. On the basis of the erosion test results and of the observed behavior of the levees during the hurricane, a chart is presented which can be used to select soils for overtopping resistance. Numerical simulations were performed using the program CHEN 3D to obtain the distribution of velocity vectors in the overtopping flow and of shear stresses at the interface between the water and the levee surface. The comparison of the numerical simulation results and of the erosion function gives added credibility to the proposed levee overtopping erosion chart.

Is Matric Suction a Stress Variable

Abstract: The writer attempts to clarify and address two fundamental questions regarding the appropriate use of matric suction in unsaturated soil mechanics: Is matric suction a stress variable? and Is matric suction a stress state variable? These questions are examined by employing the universally accepted mechanical equilibrium principle, the concept of representative elementary volume (REV) for air-water-solid multiphase porous media, and physical and logical reasoning. It is clarified that matric suction is not a stress variable at a typical air-water-solid REV level, and it can be considered as a stress state variable. However, when it is considered as a stress state variable, there is an interdependency or coupling between matric suction and the net normal stress if both of them are concurrently used to describe the state of stress in unsaturated soils. It is illustrated that the answers to these questions bear important implications for the conceptualization, theorization, and application of unsaturated soil mechanics.

Probability and Risk of Slope Failure

Abstract: This paper aims to demystify the use of risk assessment as a decision management tool and present a methodology that places quantitative risk assessment within reach of every geotechnical engineer, even for routine engineering assignments. In particular, we propose using quantification of expert judgment (i.e., subjective probabilities) as a practical alternative for determining probability of slope failure. The writers present a semiempirical relationship between factor of safety and annual probability of failure that permits estimation of slope failure probabilities with relatively modest effort. The case study for a tailings dam shows that risk assessment based on quantification of expert judgment provides a framework to arrive at rational management and engineering decisions related to dam safety and other geotechnical problems. Using the semiempirical relationship presented here, practicing engineers can use this helpful tool by applying their current skills.

Centrifuge Modeling of Earthquake Effects on Buried High-Density Polyethylene (HDPE) Pipelines Crossing Fault Zones

Abstract: Permanent ground deformation is a severe hazard for continuous buried pipelines. This technical paper presents results from four centrifuge tests designed to investigate the influence of pipe-fault orientation on pipe behavior under earthquake faulting. The experimental setup and procedures are described, and the test results are presented. The test results show that, as expected, pipe axial strain is strongly influenced by the pipe-fault orientation angle, whereas the influence of pipe-fault orientation angle on pipe bending strain is minor. The measured pipe strains were shown to follow the trend predicted by the Kennedy model. Also, through a parametric study using the Kennedy model, the experimental data were extrapolated for cases of pipeline with longer unanchored length. By combing the data from strain gauges and tactile pressure sensors, transverse force–deformation relations or p–y relations for the pipe were determined. The data indicates that the underlying p–y relationship varies along the len...

Effect of Penetration Rate on Cone Penetration Resistance in Saturated Clayey Soils

Abstract: In this paper, the effects of penetration rate on cone resistance in saturated clayey soils are investigated. Shear strength rate effects in clayey soils are related to two physical processes: the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained. Special focus is placed on this second effect. Cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber, and the resulting data were analyzed. The field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table. Additionally, tests with both cone and flat-tip penetrometers in sand-clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained. A series of flexible-wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation, which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained. A correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests.

Economic Design Optimization of Foundations

Abstract: A geotechnical foundation design should address at least three basic requirements: ultimate limit state (ULS), serviceability limit state (SLS), and economics. Most conventional design approaches focus on ULS and/or SLS optimization, with economics being evaluated afterwards. As an alternative, this paper develops a design approach that explicitly considers the construction economics and results in a foundation that has the minimum construction cost. This design approach is expressed as an optimization process, in which the objective is to minimize construction cost, with the design parameters and design requirements as the optimization variables and constraints, respectively. This design approach is illustrated using a spread footing example. Because construction costs vary by locale, the economically optimized designs differ regionally. Sensitivity studies on soil properties and design requirements show that, for typical spread footing designs in cohesionless soils, Young’s modulus (E) and the effective...

Relationships between In Situ and Roller-Integrated Compaction Measurements for Granular Soils

Abstract: To evaluate compaction meter value and machine drive power roller-integrated compaction technologies, a field study was conducted with 30-m test strips using five granular materials. The test strips were compacted using a prototype CS-533E vibratory smooth drum roller and tested for various compaction parameters using in situ test methods (e.g., nuclear moisture density, dynamic cone penetrometer, plate load tests, etc.). To characterize the roller machine-ground interaction, soil testing focused on measuring soil compaction parameters of the compaction layer, to a depth not exceeding 300 mm . The experimental testing of five test strips provided roller data and in situ measurements for several stages of compaction that were used in performing statistical regression analyses. The relationships between data from the roller-integrated compaction technologies were investigated with special consideration for the relative variation that was observed for each measurement system. Statistical averaging mitigated ...

Underwater Shake Table Tests on Waterfront Structures Protected with Tire Chips Cushion

Abstract: A series of large-scale underwater shaking table tests was performed on a gravity type model caisson protected by a cushioning technique using tire chips (scrap tire derived recycled product). The function of the tire chips cushion is to reduce the load and restricting the permanent displacement of such waterfront retaining structures during earthquakes by exploiting the compressibility, the ductility and the energy absorbing capacity of tire chips. The seismic performance of such earthquake resistant techniques was evaluated by subjecting the soil-structure system into three different earthquake loadings (two actual earthquake records and one synthetic earthquake), and measuring the respective responses. The results demonstrated that the seismic load against the caisson quay wall could be substantially reduced using the proposed technique. In addition, the presence of the protective tire chips cushion could significantly reduce the earthquake-induced residual displacement of the caisson quay wall.

Penetration Resistance of Offshore Skirted Foundations and Anchors in Dense Sand

Abstract: Penetration of skirts is an essential design issue for offshore skirted foundations and anchors in sand. Skirts may not penetrate far enough into dense sand by the available submerged weight alone. It may therefore be necessary to apply underpressure inside the skirt compartment to produce an increased driving force and to reduce the penetration resistance. This paper recommends procedures to calculate penetration resistance and required underpressure for skirts penetrated in dense sand with and without interbedded clay layers. The recommendations are based on interpretation of skirt penetration data from prototypes, field model tests, and laboratory model tests in dense sand. The paper first presents a model to calculate the penetration resistance of skirts penetrated by weight, or other external vertical load that does not cause flow of water in the sand. Two models are considered; one based on bearing capacity equations with friction angles from laboratory tests, and the other one based on empirical correlations with CPT tip resistance. The bearing capacity model gives more consistent correlations with the empirical data than the CPT model. Thereafter, a model to account for the effect of underpressure applied inside the skirt compartment is proposed. This model is developed based on interpretation of available prototype and model test data from skirts penetrated by underpressure. The results show that underpressure facilitates skirt penetration in sand considerably by providing both an additional penetration force and a reduced penetration resistance. It is also shown that interbedded clay layers can prevent flow of water through the sand and eliminate the beneficial reduction in penetration resistance.

Suction-Controlled Laboratory Test on Resilient Modulus of Unsaturated Compacted Subgrade Soils

Abstract: Conventionally, the resilient modulus test is conducted in the laboratory under different moisture content in which matric suction is unknown during the test. To investigate the influence of the matric suction on the resilient modulus, this study integrated the suction-controlled testing system and developed a modified testing procedure for the resilient modulus test of unsaturated subgrade soils. Based on the axis-translation technique, two cohesive soils were tested to investigate the effect of matric suction on resilient modulus. In the modified testing procedure, in order to fulfill the equilibrium in matric suction, the number of load cycles at each loading sequence of the resilient modulus test (AASHTO T 292-91) needs to be increased significantly. Experimental data indicate that matric suctions measured in the specimen after consolidation and resilient modulus tests are consistent with the matric suctions deduced from the soil-water characteristic curve corresponding to the same moisture content. In general, the resilient modulus obtained by the suction-controlled resilient modulus test appears to be reasonable. The trends of resilient modulus obtained by the suction-controlled resilient modulus test are consistent with those obtained by the conventional resilient modulus test. However, the suction-controlled resilient modulus test provides better insights that can help in interpreting the test results.

Durability of Cement Stabilized Low Plasticity Soils

Abstract: Three testing methods for predicting the durability of cement-stabilized soils—the tube suction (TS), 7-day unconfined compression strength (UCS), and wetting–drying durability tests—were tested and compared for their correlations and influence factors using a problematic low plastic silt clay from subgrade commonly encountered in Louisiana. A series of samples was molded at six different cement dosages (2.5, 4.5, 6.5, 8.5, 10.5, and 12.5% by dry weight of the soil) and four different molding moisture contents (15.5, 18.5, 21.5, and 24.5%). The test results indicate that the water–cement ratio of cement-stabilized soil had the dominant influence on the maximum dielectric value (DV), 7-day UCS, and durability of stabilized samples tested, although the dry unit weight of cement-stabilized soil could cause the variation of the results. This study confirms that TS, 7-day UCS, and wetting-drying durability tests are equivalent in predicting durability, and tentative charts to ensuring the durability of cement-...

Numerical Simulation of Vertical Pullout of Plate Anchors in Clay

Abstract: The behavior of strip and circular plate anchors during vertical pullout in uniform and normally consolidated clays was studied in this paper by means of small strain and large deformation finite-element analyses. Both fully bonded (attached), and “vented” (no suction on rear face), anchors were considered. The current numerical results were compared with existing laboratory test data, finite-element results, and analytical solutions. This study showed that, in small strain analysis, the scatter of existing data was mainly due to the effect of soil stiffness. In large deformation analysis, when soil and anchor base were attached with suction, the pullout capacity factor formed a unique curve independent of the soil strength ( su ) , soil effective unit weight ( γ′ ) and anchor size ( B =width of strip anchor and D =diameter of circular anchor). The transitional embedment depth ratio, HSD ∕B or HSD ∕D , (where HSD =transition depth between shallow and deep embedment) was 1.4 for a strip anchor and 0.75 for...

Modified Direct Shear Test for Anisotropic Strength of Sand

Abstract: This paper presents a simple method to estimate the directional dependency of granular soil strength using a modified shear box and a special specimen preparation procedure. This method is used to investigate the strength anisotropy of granular materials with particle shapes varying from spherical to angular. The experimental results show that the friction angle of granular materials varies with the orientation of shear plane relative to the bedding plane, and the degree of anisotropy is affected by particle shape. Comparison of the data from direct shear tests in this study with those of plane strain and torsional simple shear tests in the literature shows that direct shear using the modified direct shear box can reasonably capture the directional dependency of the friction angle for cohesionless materials.

Predicting the Erosion Rate of Chemically Treated Soil Using a Process Simulation Apparatus for Internal Crack Erosion

Abstract: Chemical stabilization is an effective ground improvement technique for controlling erosion. Two stabilizers, lignosulfonate and cement, were used to study how effectively they could stabilize erodible silty sand collected from Wombeyan Caves, NSW, Australia. To conduct this research, four dosages of cement (0.5, 1, 1.5, and 2%) and four dosages of lignosulfonate (0.1, 0.2, 0.4, and 0.6%) by dry weight of soil were selected. All treated and untreated soil specimens were compacted to 90 and 95% of their maximum dry density to study the effect of compaction level on erodibility. The erosion characteristics of treated and untreated soil samples were investigated using a process simulation apparatus for internal crack erosion designed and built at the University of Wollongong. The findings of this study indicated that both chemical stabilizers increased the resistance to erosion because of their cementing properties. It was also found that the critical shear stress increased linearly with the amount of stabilizer, and the coefficient of soil erosion decreased as a power function of the critical shear stress.