Influence of Gravel on the Compression Characteristics of Decomposed Granite Soil

Large-scale one-dimensional compression tests were performed in order to analyze the influence of gravel on the compression properties of gravel-mixed decomposed granite soils. After adjusting the gravel contents of the said soil, specimens compacted at a certain level of compaction energy and water content were tested. Based on the test results, it was observed that when gravel-mixed decomposed granite soil was compacted at the same energy level, there existed a specific gravel content at which the dry density was maximum and which also produced the minimum compression index. Furthermore, an expression based on two-phase mixture theory was proposed to quantitatively evaluate the effects of gravel content through a material parameter calculated using the theory, and the estimated compression curves agreed very well with the results of the experiments.     

Influence of Stress Ratio and Stress Path on Behavior of Loose Decomposed Granite

This paper presents results from four series of triaxial compression tests of loosely compacted decomposed granite (DG) or silty sand on both isotropically and anisotropically consolidated specimens. These tests included undrained tests, drained tests with constant deviator stress, and a decreasing mean effective stress path. The silty sand possessed high compressibility during isotropic compression. The observed high compressibility is probably attributed to the loose soil structure created by using the moist tamping method and the presence of crushable feldspar in the soil. Static liquefaction behavior and the so-called “reversed” sand behavior were observed in all undrained tests. This “reversed” sand behavior can be readily explained by the high compressibility of DG leading to the nonparallel and converging nature of the initial state line and the critical state line. Preshearing resulted in a more brittle response in the postpeak behavior. The higher the initial stress ratio (ηc), the smaller the ductility. Structural collapse of DG was observed. This collapse is characterized by a sudden large increase in both the axial and contractive volumetric strains. The mobilized angles of friction at collapse range from 31.8° to 38.7°, which are smaller than the critical state angle (?col′), but higher than the mobilized friction angle of the instability line (28.1°) determined by the isotropically consolidated undrained tests. A trilinear approximate relationship can be found between ?col′ and ηc and a liquefaction potential index is introduced to provide a simple preliminary design parameter for static liquefaction and instability prone slopes.     

Behavior of a Compacted Completely Decomposed Granite Soil from Suction Controlled Direct Shear Tests

A series of single-staged consolidated drained direct shear tests are carried out on recompacted completely decomposed granite (CDG) soil—a typical residual soil in Hong Kong, under different matric suctions and net normal stresses. Matric suction is controlled by applying air pressure in the pressure chamber and water pressure at the bottom of the high air-entry ceramic disk. The experimental results show that the contribution of suction to shear strength is significant. Shear strength of CDG soil increases with the increase of matric suction. Net normal stress has a remarkable influence on the shear strength of unsaturated CDG soil. The increase in shear strength due to an increase in matric suction (suction envelope) is observed as nonlinear i.e., ?b value varies with matric suction. No soil dilatancy is observed for zero matric suction (saturated case) but as the suction value is increased, higher soil dilatancy is obvious in lower net normal stresses. The rate of increase of soil dilatancy is greater in lower suction range than in higher suction range. The experimental shear strength data match closely with the shear strength predicted by existing shear strength model considering the soil-dilation effect.     

Influence of Amorphous Clay-Size Materials on Soil Plasticity and Shrink-Swell Behavior

The influence of amorphous clay-size materials on geotechnical engineering properties is recognized only for soils developed from volcanic ash under extremely wet, alumina-rich soil environments (called Andisols). The objective of this study was to quantify the amorphous clay-size materials in less weathered volcanic soils that are rich in silica, and to determine the influence of the amorphous materials on plasticity and shrink-swell behavior of these soils. Soil and weathered rock samples were taken from a slow-moving landslide site in Honolulu. Quantification of amorphous and crystalline clay content was performed with x-ray diffraction and the Rietveld method. Atterberg limits and shrink-swell potential of the soil samples were determined. The results showed that clay-size fraction in both soil and weathered rock samples were predominantly amorphous (55–74% in soil and 48–63% in weathered rock). Smectite and halloysite were the primary crystalline clay minerals, constituting about 15–30% of the clay fraction in soils. Atterberg limits of the soil ranged from 65 to 135 for liquid limit, from 30 to 40 for plastic limit, and 9 to 25 for shrinkage limit. Volumetric free swell ranged from 2 to 21%. The plasticity and shrink-swell potential increased with increasing the content of amorphous clay-size materials in the soil. Air drying and oven drying did not significantly change the plasticity. The study concluded that silica-rich amorphous materials dominate the clay mineralogy of the soils studied, resulting in the plasticity and shrink-swell behavior similar to that of smectite-rich soils and distinct from that of Andisols.     

Behavior of Concrete in Water Subjected to Dynamic Triaxial Compression

To understand the behavior of concrete material in ambient water, a series of triaxial compressive tests of concrete cylindrical specimens (? 100×200?mm) was conducted on a large scale triaxial machine. The acting pattern of water, confining pressure, loading strain rate, and moisture content were chosen as test parameters. The water acting patterns on concrete were directly divided into mechanical loading and real water loading according to whether the specimens were directly exposed to water or not. The confining pressure ranged from 0–8 MPa and the strain rate included 10?5/s, 10?3/s, and 10?2/s. By testing dry and saturated specimens, the effect of moisture on concrete strength was also examined. The test results indicated that the compressive strengths of both dry and saturated concrete increase obviously with the confining pressure under mechanical confining pressure. However, the effect on the strengthened dry concrete specimens is more significant. The strength of dry concrete under real water loading decreased remarkably, even less than its uniaxial strength, whereas the compressive strength of the saturated concrete specimen under real water loading is close to its uniaxial compressive strength. The strength of concrete increases with strain rate, and this phenomenon becomes more apparent under water loading.     

Compression and Shear Behavior of Mudstone Aggregates

In this paper, a staged compression–immersion–direct shear test was conducted on the compacted samples of crushed mudstone aggregates, and its compressive and shear behavior are discussed with attention to cementation effects. Compression behavior of the compacted samples was influenced significantly by the compaction degree as expected. So were the shear behavior and shear strength. Immersion caused an additional compression and a reduction in mobilized shear stress and in the dilatant nature during shear at low applied pressure levels. Moreover, immersion reduced significantly the peak shear strength parameter c with only a little change in ?. The compression lines and critical state lines of the nonimmersed and immersed specimens seem to parallel each other, and the compression line of the nonimmersed and the critical state line of the immersed form the upper and lower bounds, respectively. A gap between the shear stress–void ratio lines of the specimens with and without immersion can be considered to represent a combined effect of cementation retained in a crushed mudstone aggregate itself and an interlocking effect of aggregates.     

热压缩2091 Al-Li合金的流变应力行为

采用Ｇｌｅｂｌｅ１５００高温等温压缩试验研究了一种２０９１铝锂合金高温塑性变形时的流变应力行为。结果表明，应变速率和变形温度的变化影响合金稳态流变应力的大小，稳态流变应力与真应力大小无关。应变速率和流变应力之间满足双曲正弦关系，温度和流变应力之间满足Ａｒｈｅｎｉｕｓ关系。可用包含Ａｒｈｅｎｉｕｓ项的ＺｅｎｅｒＨｏｌｌｏｍｏｎ参数描述２０９１合金高温塑性变形时的流变应力行为。     

Integral Abutment-Backfill Behavior on Sand Soil—Pushover Analysis Approach

This paper presents a study on the behavior of the abutment-backfill system under positive thermal variation in integral bridges built on sand. A structural model of a typical integral bridge is built, considering the nonlinear behavior of the piles and soil-bridge interaction effects. Static pushover analyses of the bridge are conducted to study the effect of various geometric, structural, and geotechnical parameters on the performance of the abutment-backfill system under positive thermal variations. The shape and intensity of the backfill pressure are found to be affected by the height of the abutment. Furthermore, the internal forces in the abutments are found to be functions of the thermal-induced longitudinal movement of the abutment, the properties of the pile, and the density of the sand around the piles. Using the pushover analysis results, design equations are formulated to determine the maximum forces in the abutments and the maximum length of integral bridges based on the strength of the abutments. Integral bridges with piles encased in loose sand and oriented to bend about their weak axis, abutment heights less than 4?m, and noncompacted backfill are recommended to limit the magnitude of the forces in the abutments.     

Visualization of Crushing Evolution in Granular Materials under Compression Using DEM

Granular materials forming part of natural slopes, embankments, subgrades of foundations, and pavement structures are subjected to both static and dynamic loads during their engineering lives. As a result of these loads, particle crushing may occur. The present study demonstrates that the discrete-element method (DEM) can be used to visualize the evolution of this breakage process. In particular, the evolution of crushing in a simulated granular material subjected to uniaxial compression is presented. Even though DEM does not normally consider particle breakage, it is possible to simulate crushing by replacing one particle that has failed in tension with a combination of many particles of different sizes. The results from the simulation indicate that crushing does not develop uniformly throughout the sample, but rather concentrates in certain regions. These observations agree with experimental results of uniaxial tests conducted on sand. Other results from the simulation satisfactorily agree with experimental results previously reported by other researchers. In this way, by using a simplified failure criterion, DEM can be used to visualize and understand the evolution of granular crushing. This is something that is very difficult to do with laboratory tests alone.     

Elastoplastic Damage Behavior of a Mortar Subjected to Compression and Desiccation

This paper deals with experimental investigation and numerical modeling of drying effects on the mechanical behavior of cement-based materials. First, the main results from an experimental study on the mechanical behavior (failure strength, induced damage, and plastic deformation) of a mortar subjected to the desiccation process are presented. Then, a coupled elastoplastic damage model is proposed to describe the mechanical behavior of cement-based materials subjected to tensile and compressive stresses. A particular emphasis is put on the pressure sensitivity of plastic flow and damage evolution. Capillary effects on mechanical behavior due to desiccation have been taken into account in the framework of partially saturated porous media. Finally, numerical simulations and experimental data are compared in order to verify the capacity of the model to reproduce the basic characteristics of the mortar in saturated and unsaturated conditions.     

Effect of Interparticle Friction on the Cyclic Behavior of Granular Materials Using 2D DEM

This study presents the influence of the interparticle friction angle on the cyclic behavior of granular materials using the two-dimensional (2D) discrete-element method (DEM). The numerical sample was modeled with oval-shaped particles, whereas the isotropically compressed dense sample was prepared from the initial sparse sample using periodic boundaries. Biaxial cyclic shear tests were simulated with different interparticle friction angles. It was noted that the width of the stress-strain cyclic loops becomes thin when the interparticle friction angle increases. It was also noted that the induced fabric anisotropy is more pronounced during unloading than loading. Moreover, a strong correlation between macro- and microquantities was observed for strong contacts during cyclic loading.     

Creep-Effect on Mechanical Behavior of Concrete Confined by FRP under Axial Compression

Despite many successes in concrete creep studies, its effect on the mechanical behavior of concrete members is far from a thorough case-specific understanding. For the members that have been subjected to a long-term load, the classical stress-strain models describing the short-term behavior of either confined or unconfined concrete are unsuitable. In order to investigate this creep-effect, an experiment on eight concrete cylindrical columns confined by fiber-reinforced polymer (FRP) is carried out. Based on the theory of plasticity for concrete, a constitutive model that takes into account the effect of creep on mechanical behavior of concrete confined by FRP is presented. In the model, the creep law inspired in the microprestress-solidification theory is generalized to triaxial stress condition for the calculation of the creep of the concrete columns confined by FRP. The predictions of the model agree well with the experimental results. The present study indicates that the creep increases the elastic modulus, slightly decreases the compressive strength, and degrades the deformation capability of the concrete confined by FRP.     

Effect of Nonlinear Soil Behavior on Inelastic Seismic Response of a Structure

The characteristics of the earthquake motions at the base of a structure are affected by the properties of the underlying soil through the soil amplification and soil–structure interaction phenomena. In this paper the effect of nonlinear soil behavior on the elastic and inelastic response spectra of the motions that would be recorded at the free surface of a soft soil deposit or at the base of each structure is investigated. The analyses are conducted for a soil layer by itself and for a complete soil structure system using a finite element discretization of the soil in cylindrical coordinates and an approximate linear iterative procedure to simulate nonlinear behavior. Studies are conducted for structures, with a constant base and variable height modeled as equivalent linear or nonlinear single degree of freedom systems and an input motion at the base of the soil deposit representative of rock outcrop motions. Both mat and pile foundations are considered. The results illustrate clearly the importance of the nonlinear soil behavior.     

Influence of Particle Properties and Initial Specimen State on One-Dimensional Compression and Hydraulic Conductivity

Particle crushing can adversely affect geotechnical system performance; examples include clogging in wells, pile shaft capacity degradation, and postconstruction settlements. The generation of fines results in volumetric compression and a reduction hydraulic conductivity, which is important for geotechnical systems whose performance is directly dependent on pore pressure dissipation, groundwater flow, or hydraulic pumping. Knowledge of hydraulic conductivity change is poorly understood due to limited experimental data, and an ability to predict this change is lacking. The role of single particle properties, initial specimen state conditions, and loading conditions on the evolution of hydraulic conductivity with particle crushing was examined experimentally. Specimen response exhibited an overshoot behavior and the convergence to a unique condition independent of initial relative density, gradation, and particle shape. The hydraulic conductivity decreased by 2–3 times before specimen yield, and by 2–3 orders of magnitude after specimen yield. Empirical correlations were developed to estimate the change in hydraulic conductivity given the initial permeability and select crushing parameter values at the stress level of interest.     

Minimum Depth of Soil Cover above Soil–Steel Bridges

Soil–steel bridges are built of flexible corrugated steel panels buried in well-compacted granular soil. Their design is based on the composite interaction between the soil pressures and the displacements of the conduit wall. The structure failure could be initiated by shear or tension failure in the soil cover above the steel conduit. The provisions for design given in different codes, such as the Canadian Highway Bridge Design Code, managed to avoid some of the problems associated with the failure of soil above soil–steel bridges by requiring a minimum depth of soil cover over the crown of the conduit taking into consideration the geometric shape of the conduit. However, the present code requirements for a minimum depth of cover were developed for a maximum span of 7.62 m and using nonstiffened panels of 51 mm depth of corrugation. The effect of having larger spans or using more rigid corrugated panels has not been examined before and is the subject of this paper. The present study uses the finite-element analysis to re-examine the possible soil failures due to centric live loads (i.e., loads acting symmetrically about the mid span of conduit) or eccentric live loads. The study deals with spans up to 15.24 m of circular conduits and 21.3 m of arches with deep corrugations. It has been found that, in addition to the conduit geometry, the actual dimension of the span should be considered to determine the required depth of soil cover.     

Bond Behavior of Near-Surface Mounted FRP Strips Bonded to Modern Clay Brick Masonry Prisms: Influence of Strip Orientation and Compression Perpendicular to the Strip

In this paper the results of 18 pull tests performed on clay brick masonry prisms strengthened with near-surface mounted carbon fiber-reinforced polymer (CFRP) strips are presented. The pull tests were designed to add to the existing database and investigate variables significant to masonry construction. FRP was bonded to solid clay brick masonry; FRP aligned both perpendicular and parallel to the bed joint; and in the case of FRP reinforcement aligned parallel to the bed joint, compression applied perpendicular to the strip was used to simulate vertical compression load in masonry walls. Results including bond strength, critical bond length, and the local bond-slip relationship are presented as well as a discussion on the effect of the new variables on these results.     

Calibration of Electromagnetic Induction for Regional Assessment of Soil Water Salinity in an Irrigated Valley

Electromagnetic instruments are increasingly being used for in situ analysis and mapping of soil salinity in irrigated soils. This study develops calibration models for salinity assessment over regional scales on the order of tens of thousands of hectares. These models relate apparent soil electrical conductivity measured with the EM-38 electromagnetic induction meter (Geonics Ltd.) to traditional laboratory-measured saturated paste electrical conductivities (ECe). The study area is located in the Lower Arkansas River Valley, Colo. and is divided into two regions. At each of 414 randomly selected calibration sites, an EM-38 reading was taken and multiple soil samples were extracted for analysis. The sites chosen have soil ECe values ranging from 1?to?18?dS/m, gravimetric water contents (WC) from 0.02 to 0.4, and textures ranging from sands to clays. The best model for predicting soil ECe in both study regions is bivariate nonlinear and includes EM-38 vertical readings (EMV) and WC as covariates. Uncertainty in the calibration equations is addressed and tests are conducted at 48 independent sites. Results indicate that, while uncertainty is considerable in regional scale surveys, electromagnetic instruments can be calibrated for rapid reconnaissance of soil water salinity, providing reasonably accurate identification of salinization categories.     

Design Charts for Evaluating Impact Forces on Dissipative Granular Soil Cushions

This paper concerns the problem of designing standard artificial tunnels for rock boulder protection. The proposed approach consists in uncoupling the problem of the dynamic response of the granular dissipative soil cushion placed on the top of artificial tunnels from the dynamic response of the reinforced concrete structure underneath. An already conceived elasto-viscoplastic constitutive model capable of simulating the penetration process of the boulder within the soil stratum and reproducing the force acting on the boulder is briefly described. Its simplified one-dimensional formulation is outlined. A modified version of the model, taking into account large displacements occurring when either impacts on loose granular soils or high energetic content impacts on dense sand strata are considered, is also introduced. To validate the approach, some in situ test results are numerically simulated. A simplified numerical approach is proposed for obtaining the evolution with time of both impact force and boulder penetration, bypassing the use of the rheological model. This goal is achieved by introducing some abaci obtained numerically with reference to an ideal dense sand soil stratum of reference.     

Air Binding of Granular Media Filters

Air bubbles that form in water treatment filters create headloss and can form whenever the total dissolved gas pressure exceeds the local solution pressure. The location of potential bubble formation in filters can be predicted based on measurements of the clean bed headloss with depth, flow rate, and the influent total dissolved gas concentration. Bubble formation within filters can be reduced by increasing the pressure within the filter via greater submergence (water head above the media), lower hydraulic flow rate, or using a more porous media. Bubbles trapped in the bed can be released by “burping,” which can reduce the extent of headloss buildup. Burping is more significant at lower flow rates and within a lower density, higher porosity, hydrophobic anthracite layer.     

2. Numerical Simulations of Water Flow and Solute Transport Applied to Acid Sulfate Soils

Field investigations of Rassam et al. in 2001 have highlighted the effects of infiltration, drainage, and evapotranspiration on the dynamics of water flow and solute transport in acid sulfate (AS) soils. In this work, HYDRUS-2D is adopted as the modeling tool to elucidate the trends observed in that field experiment. Hypothetical simulations have shown that the relative contribution of drains to lowering the water table is significant only when closely spaced drains are installed in coarse textured soils, evapotranspiration being the main driving force in all other cases. AS soils reaction products that are close to a drain are readily transportable during infiltration and early drainage, but those produced farther away from it near the midpoint between drains are only slowly transported during a prolonged drainage process. Simulating the field trial of Rassam et al. has shown that drain depth and evapotranspiration significantly affect solute fluxes exported to the ecosystem. Managing AS soils should target minimal drain depth and density. Partial or full lining of the drains should be considered as a management option for ameliorating the environmental hazards of AS soils.