Strength Characteristics Of Soil Research Articles

Effect of triaxial specimen size on engineering design and analysis

Triaxial tests are often used to determine the behavior and strength characteristics of soils. Specimen size can have a significant impact on the measured shear strength. Accordingly, the selected parameters affect the related geotechnical engineering analysis and design. We tested three different specimen sizes of loose Ottawa sand in triaxial compression tests. The measured shear strength and friction angle are used to explain some of the observed scale effects in engineering design and analysis. Critical state parameter and shear strength from the laboratory tests are employed to assess the static and seismic slope stability of an embankment dam, to calibrate a critical state soil constitutive model, to study the soil behavior under shallow foundations, and to evaluate liquefaction triggering and failure of retaining structures. We show that all of these analyses can be significantly affected by the choice of the specimen size used to determine shear strength parameters. While using small size samples for determining shear strength parameters might result in un-conservative design, a large sample size is consequently a more accurate representation of soil strength conditions and field deformations.

Specimen size effects on behavior of loose sand in triaxial compression tests

Triaxial tests are often used to determine the behavior and strength characteristics of soils without due attention to the differences in specimen size. Several drained and undrained monotonic triaxial compression shear tests are performed in this study on three different specimen sizes of the same sand to investigate the influence of specimen size and scale effect on sand compression and shear behavior. The behavior of a sand specimen is strongly influenced by shear banding and specimen boundary conditions, which are manifested as specimen size effects in the test results of this study. The measured sand compressibility and shear strength parameters are employed to describe scale effects, and investigate specimen size effects in liquefaction triggering analysis. The results show that while larger specimens exhibit a less compressible behavior during isotropic compression, larger shear strengths and effective friction angles are mobilized in the smaller specimens during shearing. A number of geotechnical analyses can be significantly affected by variations in strength parameters of the same soil determined from different specimen sizes. While using small size specimens for determining shear strength parameters might result in an unconservative design, a large specimen size provides a more accurate representation of different soil strength conditions and field deformations.

Study of scale effect on strength characteristic of stabilised composite with sewage sludge – Part B: Critical investigation

The preliminary study of the engineering properties of bentonite composites with and without added sludge by testing the pH, compaction, and consolidation has been discussed in part A. Further critical investigations were then performed to gain an understanding of the scale effect on soil strength characteristics and the microanalytical behaviour of soil composites. Research using two different sized direct shear boxes yielded more applicable data for applying to in situ soil. It was revealed that soil was slightly strengthened by the utilisation of sludge. Experimental data were then confirmed by further microstructural, chemical, elemental and mineralogical tests.

Investigation on Effect of Soil Strength Characteristics on Excavating by Narrow Blade

Investigation on Effect of Soil Strength Characteristics on Excavating by Narrow Blade

Grain size distribution of soils within the Cordillera Blanca, Peru: An indicator of basic mechanical properties for slope stability evaluation

This paper presents results of a study on the mechanical properties of sandy and gravely soils within the Cordillera Blanca, Peru. The soils were divided into groups according to their origin (glacial, fluvial, or debris flow). The grain size distribution of forty three soil samples was used to classify the soils according to the scheme of the Unified Soil Classification System (USCS). These distributions have then been used to estimate shear strength and hydraulic properties of the soils. There are clear differences between the soils which reflect their divergent origins. The glacial soils normally fit within one of two distinctive groups according to the proportion of fines (Group A, 7%-21.5%; Group B, 21%-65%). The estimation of shear strength at constant volume friction angle and peak shear strength of the glacial sediments with low content of fines was made using published data relating to the measured shear strength characteristics of soils with similar origins and grain size distributions. The estimated values were supported by measurements of the angle of repose taken from fourteen samples from two moraines and by shear tests on samples from one locality. The results of the grain size distribution were also used to estimate the average hydraulic conductivity using the empirical Hazen formula which results were verified by field infiltration tests at two localities.

굴착시공 중 취약지반구간에서 터널변위 거동 연구

차량의 양호한 주행성능 확보를 위한 터널공사의 증가와 더불어 터널시공 중 터널 붕락 및 과다변위 발생사례가 증가하고 있다. 터널공사의 특징이 지반의 강도특성을 최대한 이용하는 경험적인 시공방법이라는 측면에서 터널붕락 및 과다변위 발생사례에 대한 붕락 및 과다변위 발생 원인분석이 중요하다. 따라서 본 논문에서는 취약지반조건에서 대표적인 붕락 및 과다변위 발생사례의 붕락 원인에 대하여 분석하였다. 분석결과, 국지성 강우량의 증가, 시공 중 계측값의 지속적인 증가, 단층파쇄대가 지표면까지 연결되는 지반조건이 공통적으로 존재하는 경우 대규모 붕락 또는 과다변위가 발생한 것으로 분석되었다. The tunnel construction is increasing in order to secure a good driving performance of the car and train. A cases of tunnel collapse and the tunnel excessive displacement are increasing with the increase in tunnel construction. In terms of empirical construction methods using the strength characteristics of soil, it is important for tunnel construction to analyze causes of collapse and displacement. In the paper, it was analyzed the causes of collapse and excessive displacement of tunnel in the fractured ground condition. The results of analysis is that the increase of rainfall and lasting increase of displacement and large scale fractured ground are interconnected.

Метод расчета свайных ленточных фундаментов при образовании карстового провала

The paper presents pile strip foundations in the areas with karst risk. The analysis of karst hole formation mechanism shows the lateral soil pressure on the piles caused by the downfallen soil on the hole rims, which transfers around the hole edges during karst hole formation. In this case, the horizontal pressure of the pile reactive force in the area of the pile connection with the raft is transferred to the raft. Pile failure at the hole boundaries will lead to the increase of the raft bearing distance above the karst hole. The inadequate raft bearing capacity can provoke the emergency situation. The existing Codes on karst protective foundations design do not contain the analysis of pile and raft horizontal pressure under the downfallen soil.The goal of this work is to develop the method of pile strip foundations analysis in the areas with karst risk in case of karst hole formation. The analysis of stress-strain state of the system “foundation soil — pile foundation” was carried out using numerical modeling in geotechnical program MIDAS GTS. As a result of numerical investigations, the diagrams of lateral soil pressure onto the piles and the raft are plotted. The pile pressure is approximated with the linear or bilinear function in dependence on geometrical dimensions of the karst hole and strength characteristics of soil that generates the horizontal pressure.In the Codes, the analysis of a pile under lateral soil pressure is given for a pile with the free end. In the problem examined, the pile head has the hinged bearing in place of the connection with the raft. In view of the given boundary data, the pile design scheme is plotted. The inner forces and displacements of the pile are determined by integrating the differential equation of a pile bending. The consistent integrations are evaluated out of the boundary conditions. The boundary values of inner forces and displacements are evaluated from the equality conditions of displacements and inner forces in the pile at the level of the hole bottom that are evaluated in turn for the upward and downward pile section. The method of pile analysis is developed in case of lateral soil pressure approximation with the linear function.The method worked out allows recalculating a pile being at the edge of the karst hole and accepting the lateral pressure of the downfallen soil on the hole edges.

Effect of Strain Rate on the Strength Characteristics of Soil–Lime Mixture

The effects of rate of strain on strength and deformation characteristics of soil–lime were investigated. Five strain rates (0.1, 0.8, 2.0, 4.0 and 7.0 %/min), five lime contents (0, 3, 6, 9 and 12 %) by dry soil weight and three cell pressures (100, 200 and 340 kN/m2) were carried. Triaxial tests, under unconsolidated condition, were used to study the effect of strain rate on strength and initial modulus of elasticity of soil and soil–lime mixture after two curing periods 7 and 21 days, respectively. A total of 405 triaxial specimens have been tested, where 225 specimens have been tested with first curing period (7 days). The testing program includes nine specimens for each strain rate, and each lime content was carried out, including natural soil with zero lime content. Another set of triaxial tests with a total of 180 specimens for the second curing period (21 days) was prepared at optimum moisture content, and the corresponding maximum dry density was also tested. The effects of strain rate and curing period on each of stress–strain behavior, type of failure, deviator stress at failure, cohesion and angle of internal friction and initial modulus of elasticity were studied thoroughly for the natural soil as well as soil–lime mixtures. For natural soil, the test results showed that the undrained shear strength, the initial modulus of elasticity and the cohesion increase significantly as the strain rate increase, while for soil–lime mixture at different curing periods, the undrained shear strength, initial modulus of elasticity and the cohesion increases to a maximum and then decreases as the strain rate and lime content increase. Also, the same variables and angle of internal friction increase with increasing curing period.

Effect of Natural Resin on Strength Parameters of Sandy Soil

Nowadays, strength characteristics of soils have more importance due to increasing building loads. In some projects, geotechnical properties of the soils should be improved. Geotechnical engineers generally use waste materials to improve soil properties but most of these materials have toxic substances such as heavy metal slags, fly ash, silica fume and industrial resins. In this study, the effects of the addition of a plant gum, named as astragalus, grown commonly in Central and East Anatolia, Iran, Iraq, Turkmenistan and Transcaucasia, on the stability and strength parameters of cohessionless soil were investigated. Astragalus is a pure natural and environmental friendly material. Ground water directly affected by soil additives which used for soil improvement. In this investigation, properties of a cohessionless soil were stabilized by using astragalus. In order to find out which rate of the additive caused maximum strength parameters of the soil samples which prepared by using four different replacement amounts of 0%, 3%, 5% and 10% by weight of soil. Maximum dry densities and optimum moisture contents were determined for each mixture. Strength parameters of each mixture were also determined. According to experimental study, adding 1% of astragalus content is convenient for sandy soil when considered strength parameters and economical respect of additive material. I. I NTRODUCTION Human beings use soil as building and foundation material to build homes and roads through the ages. Geotechnical properties of an soil can be improved in two ways: compaction and mixing with additive material such as lime, cement, fly ash, natural materials etc. In this paper, geotechnical properties of an embankment soil were improved. The soil was taken from a commercial sand pit in Elazig City. Effects of a plant gum, named as astragalus, on the strength parameters of the sandy soil were studied. Geotechnical properties of the sandy soil were determined. Maximum dry density and optimum moisture content of the sandy soil also found out. Samples were prepared by using four different replacement amounts of 0%, 1%, 3%, 5% and 10% by weight of soil. All samples were prepared at optimum moisture content. Shear box tests were conducted on these samples. The existing soil at a construction site cannot always be totally suitable for supporting structures. For this reason

Strength Characteristics of Soils Mixed with an Organic Acid Material for Improvement

AbstractNew eco-friendly materials for soil improvement have been developed recently for construction purposes in civil engineering. An organic acid material encourages microbe proliferation over time and accelerates consolidation by biochemical penetration; soil particles are compacted by microbes and pore water is dissipated quickly. However, the effectiveness of organic acid has not yet been established. To investigate the strength characteristics of soil mixed with an organic acid, unconfined compressive strength tests were performed after aging soil samples with and without the organic acid. After 96 days of aging, the strength was generally 1.5–2.5 times greater than that without the organic acid. The pore structure of the soils was observed to change in a scanning electron microscopy analysis, and the change of total bacterial counts revealed the activity of microbes that reflects the strength characteristics. Moreover, this material is likely to be environmentally friendly according to the pH test.

Influence of Waste Tire Chips on Strength Characteristics of Soils

An experimental study was conducted to investigate the effect of waste tire chips on the strength characteristics of two soils. A cohesive clayey silt soil and a cohesionless fine sand soil were used. A program of standard Proctor tests, unconfined compression tests and California bearing ratio tests was carried out on specimens of the cohesive soil-tire mixtures, by varying tire chips content from 5% to 20% by weight of the soil. Vibratory compaction tests and direct shear tests were conducted on the cohesionless soil-tire mixtures by adding tire chips varying from 10% to 50% by weight. The results showed that 13% and 30% chip contents, respectively by weight, were optimum for composite strength of the two reinforced soil mixtures.

Effect of Random Inclusion of Polypropylene Fibers on Strength Characteristics of Cohesive Soil

This paper presents the effect of random inclusion of polypropylene fibers on strength characteristics of soil. Locally available cohesive soil (CL) is used as medium and polypropylene fibers with three aspect ratios (l/d = 75, 100 and 125) are used as reinforcement. Soil is compacted with standard Proctor’s maximum density with low percentage of reinforcement (0–1% by weight of oven-dried soil). Direct shear tests, unconfined compression tests and CBR tests were conducted on un-reinforced as well as reinforced soil to investigate the strength characteristics of fiber-reinforced soil. The test results reveal that the inclusion of randomly distributed polypropylene fibers in soil increases peak and residual shear strength, unconfined compressive strength and CBR value of soil. It is noticed that the optimum fiber content for achieving maximum strength is 0.4–0.8% of the weight of oven-dried soil for fiber aspect ratio of 100.

中国, 岷江および雑谷脳河流域地すべり土の物理的・鉱物学的性質とせん断強度特性

中国, 岷江および雑谷脳河流域地すべり土の物理的・鉱物学的性質とせん断強度特性

Effects of local scouring and saturation of soil due to flooding on maximum resistive bending moment for overturning Robinia pseudoacacia

The effects on Robinia pseudoacacia (an exotic and invasive plant in Japanese rivers) of local scouring and saturation of the soil in the root-anchoring zone due to flooding were investigated. Scouring has been defined as the removal of substrate in the root-anchoring zone, exposing the tree roots. Tree-pulling experiments were conducted, simulating flood action, and the resulting damage was examined in order to assess the effect of local scouring on the maximum resistive bending moment (Mmax) for overturning. Scouring was artificially created to three different depths, 0, 25, and 50 cm. A nonlinear model was developed that included soil strength characteristics to calculate the critical overturning moment (Mcri) under dry and saturated soil conditions. Significant correlations (p 20 cm (big) trunks. The nonlinear model was useful for determining the Mcri of R. pseudoacacia under dry and saturated soil conditions. The overturning moments of all (small, medium, and big) trees were considerably reduced under the saturated soil condition. It could be concluded that medium-sized trees were greatly affected by scouring, and that small and big trees were mainly affected by saturation of the soil under severe flooding conditions.

Root elongation, water stress, and mechanical impedance: a review of limiting stresses and beneficial root tip traits

Root elongation in drying soil is generally limited by a combination of mechanical impedance and water stress. Relationships between root elongation rate, water stress (matric potential), and mechanical impedance (penetration resistance) are reviewed, detailing the interactions between these closely related stresses. Root elongation is typically halved in repacked soils with penetrometer resistances >0.8-2 MPa, in the absence of water stress. Root elongation is halved by matric potentials drier than about -0.5 MPa in the absence of mechanical impedance. The likelihood of each stress limiting root elongation is discussed in relation to the soil strength characteristics of arable soils. A survey of 19 soils, with textures ranging from loamy sand to silty clay loam, found that ∼10% of penetration resistances were >2 MPa at a matric potential of -10 kPa, rising to nearly 50% >2 MPa at - 200 kPa. This suggests that mechanical impedance is often a major limitation to root elongation in these soils even under moderately wet conditions, and is important to consider in breeding programmes for drought-resistant crops. Root tip traits that may improve root penetration are considered with respect to overcoming the external (soil) and internal (cell wall) pressures resisting elongation. The potential role of root hairs in mechanically anchoring root tips is considered theoretically, and is judged particularly relevant to roots growing in biopores or from a loose seed bed into a compacted layer of soil.

Prediction of shear development in clean sands by use of particle shape information and artificial neural networks

Particle shape is one of the most important factors affecting the shear strength of granular soils. Regarding to the knowledge that the grain size distribution is more effective on strength characteristics of soils in comparison with the particle shape information, clean sands of similar grain size distributions and diverse particle shapes are disposed. Afterwards, shear box tests are employed on these sands to obtain the stress–strain relationships, and resulting internal friction angles. For the simulation of results, artificial neural networks (ANN) of eight architectures using three different learning algorithms are constituted. The results revealed that the network with two hidden layers utilizing Levenberg–Marquardt learning algorithm is the most successful alternative. Nevertheless, on account of the possible improvements on the database and the learning duration, scaled conjugate algorithm should be preferred, which yields mathematically congruent curves, in comparison with the experimental values. Finally, it can be underlined that, use of ANN for simulation of shear development in granular soils is promising, if the inputs and output parameters are correctly determined.

Use of geophysical methods to assess the quality of compaction of fill soils

Using the procedure of backfill and replacement of soils for the construction of water-development works and the beds of special-purpose structures in the Trans-polar region, quality control over their compaction is an inherent part of the overall production process of the construction. The potential for internal freezing of soil, the formation of ice lenses during the winter and their thawing in the summer, and the effect of groundwater and marine tides render the problem of localization of zones of loosenening of the compacted layer rather urgent during construction. Currently accepted direct point methods of evaluating the strength characteristics of soils by the extraction of samples, and boreholes do not provide desirable information on the distribution of density characteristics within the soil stratum and over the entire fill area. When the layer of fill is more than 2–3m thick, use of on-going methods of surface seismic-prospecting tomography based on the interrelation between the velocity of longitudinal seismic waves and compaction of the soil is effective [1]. Here, however, we are speaking of relative estimates of compaction in a monitoring regime that ensures undisturbed monitoring of significant areas and depths of inspection. In this statement, it is methodically necessary to solve two basic problems: establishment of the interrelation between the velocity of longitudinal seismic waves and the compaction of the soil, and the influence exerted by saturation of the soils on the results of estimates of the quality of their compaction. According to the recommendations set forth in the Construction Rules and Regulations [2], the coefficient (degree) of compaction m — the ratio of the density of the dry soil nid of the rock mass to the maximum density of the dry soil nd max, which can be attained during compaction, should be used for quality control of layer-by-layer placement of a rock mass, which is a mixture of rubbly stony soil and crushed rock in various proportions. To avoid incomplete compaction, the control scheme adopted should satisfy the condition m mdes, (1)

Developing a Texture-Based Soil Hydrologic Characteristics Model and Extending this Model to Predict Soil Strength Characteristics

Hydrologic models are used to describe water flow patterns in the soil, but there are not many models to describe the influence of soil water on soil mechanical properties. The purpose of this study was to adapt a hydrologic model to predict soil strength. In order to accomplish this goal, a new soil hydrologic characteristics model was developed using new predictive equations to improve stability and usability of the texture-based hydrologic model. This model, referred to as the Soil Texture and Compaction (STAC) model, was created to predict saturated moisture content, moisture content at 33 and 1500 kPa water tension, water tension at air entry, pore size distribution, and the saturated hydraulic conductivity given the fraction of sand and clay, and an estimate of the soil compaction. The STAC model was created using multi-variable linear regression based on mean values of the six listed hydrologic traits for each soil type. Initial estimates were improved by using density adjustments. When compared with 1717 A horizon samples, the model achieved a coefficient of determination (R2) ranging from 0.02 to 0.99 for the listed hydrologic traits, and the standard error of estimate (Se) ranged from 0.02 to 0.38. The fit is vastly improved with a good estimate of the density adjustment factor. In addition, a method is proposed to extend a soil hydraulic model to predict the soil strength. The soil strength is required to determine the tractive capability of equipment working in the field. Extending a soil hydrologic model will allow the machine tractability to be predicted in simulated surface conditions. The volumetric soil moisture content and level of soil compaction are used as independent variables to predict the cone index. The soil moisture content is determined through a hydrologic model. The soil compaction can be calculated by comparing true and expected bulk densities, or simply estimated by the user. The soil strength predictions were tested using a stochastic weather generator, soil characteristics models, and accepted soil hydrology methods for infiltration, evapotranspiration, and percolation.

Extreme pressure due to expanded cylindrical and spherical cavity in a limitless medium: applications in soil mechanics

The extreme net pressure resulting from an expansion in a cylindrical or spherical cavity within a limitless medium is studied. Performing the static and kinematic approaches of yield design theory, analytical solutions of the extreme net pressure are established for cohesive–frictional as well as for purely cohesive medium. In the case of a cylindrical cavity, the identification between the analytical extreme net pressure and limit net pressure leads to the prediction of shear strength characteristics of soil. As useful result, in soil mechanics, the assessment of correlations using pressuremeter data has been discussed. Also, some assumptions for designing foundations, from pressuremeter data, have been highlighted.

Strength characteristics of illinois coal combustion by‐product: PCC dry bottom ash

The coal combustion by‐product, dry bottom ash, originates from the burning of pulverized coal to produce electricity. Currently, almost all of the pulverized coal combustion (PCC) dry bottom ash is being dumped into ash ponds and landfills. Some of the ash ponds are reaching their maximum capacity and there is an immediate need for alternative measures to either dispose of or utilize the coal combustion by‐products for construction purposes. Within the past five years, several studies have investigated the use of PCC dry bottom ash in concrete and concrete products. However, its use in geotechnical applications is very limited. The physical properties of Illinois PCC dry bottom ash are similar to that of natural sand with particle sizes ranging from fine gravel to fine sand. Shear strength characteristics of soils, or materials similar to soils, are the most important parameters needed for the design of any geotechnical engineering project. Therefore, this study was initiated to develop understanding of the shear behavior of Illinois PCC dry bottom ash so that its potential use in geotechnical engineering applications could be accessed. This paper presents the results of an experimental study conducted to develop the technical data on shear strength characteristics of Illinois PCC dry bottom ash amended with bentonite.