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A series of large scale direct shear tests was performed to obtain the shear strength interface parameters for five different geosynthetic reinforcement materials in marginal clayey sandy soil. The performance of geosynthetic layers was evaluated at soil optimum moisture content (OMC) and high moisture content (OMC+6%) conditions. It was observed that the shear strength interface parameters dramatically decreased at 6% wet of optimum in comparison with optimum moisture content. Moreover, a comparison was made between the performance of different geosynthetic layers in a quantitative manner at target moisture content (i.e., OMC+6%). Based on the analysis of large scale direct shear test results, it was concluded that the geosynthetic layer, provided it has high drainage capability, could effectively increase the interface shear strength parameters at OMC+6% condition. [ABSTRACT FROM AUTHOR]

The physical and mechanical behavior of soil polymer composites tightly depends on the properties and structures of both soil and polymer. This study aims to investigate the effect of glass transition temperature as one of the most important characteristics of adhesive resins of acrylic polymers on the geotechnical behavior of soils that have not been fully covered by previous studies. To achieve that, three similar copolymers of methyl methacrylate-co-butyl acrylate with different glass-transition temperatures of 1°C, 33°C, and 51°C were synthesized, and two representative specimens of cohesive (kaolinite clay) and noncohesive (sand) soils were chosen to perform a full investigation of the consequential changes in the physical and mechanical behavior. A series of laboratory tests, including the Atterberg limits tests, the unconfined compressive strength tests, direct shear tests in soaked and unsoaked conditions, swelling tests, and odometer tests, were conducted on untreated and treated soils with synthesized polymers. The results showed a salient enhancement in the cohesion and the unconfined compressive strength value of both soils. However, the polymer with a glass-transition temperature near to ambient temperature led to a greater increase in the compressive and shear strength of stabilized soil among its peers. Samples treated with the polymer having the lowest glass transition temperature revealed a more compression index (i.e., obtained from odometer tests) and lower unconfined compressive strength. It is also observed that the swelling index and swelling pressure decreased marginally with increasing the glass transition temperature. [ABSTRACT FROM AUTHOR]

Mechanical behaviour of the soil–structure interface plays a major role in the shear characteristics and bearing capacity of foundations. In thermoactive structures, due to nonisothermal conditions, the interface behaviour becomes more complex. The objective of this study is to investigate the effects of temperature variations on the mechanical behaviour of soils and the soil–structure interface. Constant normal load (CNL) and constant normal stiffness (CNS) tests were performed on the soil and soil–structure interface in a direct shear device at temperatures of 5, 22, and 60 °C. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The sandy soil was prepared in a dense state and the clayey soil was prepared in a normally consolidated state. Results show that the applied thermal variations have a negligible effect on the shear strength of the sand and sand–structure interface under CNL and CNS conditions, and the soil and soil–structure interface behaviour could be considered thermally independent. In clay samples, an increase in the temperature increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The temperature rise had less impact on the shear strength in the case of the clay–structure interface than in the clay samples. The adhesion of the clay–structure interface is less than the cohesion of the clay samples. [ABSTRACT FROM AUTHOR]

In order to study how shear strength and its change in unsaturated soils modified by hydrophobic agent, sandy soils hydrophobized by dimethyldichlorosilane (DMDCS) were prepared. The hydrophobic soils with different DMDCS volume by soil mass, water content and clay content were obtained respectively. Mixtures of sandy soils (DMDCS volume by soil mass were 2 mL:100 g and 3 mL:100 g, i.e., 2% and 3%, the same below) with 3%, 5%, 7%, 11% and 13% water content were prepared respectively. Meanwhile, the mixtures of clay and sandy soils (3% DMDCS) according to the clay mass fraction of 0, 5%, 10%, 15%, 20%, 25%, 30%, 40% and 50% were prepared respectively. Then the unsaturated direct shear tests were carried out by unsaturated direct shear apparatus. Four samples in each group were prepared under the normal pressure in 100, 200, 300 and 400 kPa, respectively. The horizontal shearing ratio was 0.8 mm/min and the shearing test lasted 6 min. The results showed that: 1) The mixtures of sandy soils and DMDCS presented extreme hydrophobicity. 2) The water repelling of mixtures of clay and sandy soils was affected by both DMDCS and clay content. The water repelling of mixtures was degraded with the increasing of clay content, and improved with the increasing of DMDCS volume by soil mass. 3) The Mohr-Coulomb strength criterion could be adopted to describe the shear strength of hydrophobic sandy soils with different DMDCS and water content. With the increasing of DMDCS volume by soil mass, the shear strength index of the hydrophobic soil was decreased to different extents. The cohesive force showed a steep-drop shape from soil without DMDCS addition to that with 1% DMDCS and a slow decline up to stabilize finally. The effect of DMDCS on the cohesive force of modified sandy soils was much greater than on the internal friction angle. The hydrophobic soils’ cohesion with the increasing of water content was decreased gradually, while the internal friction angle was increased firstly and decreased finally. The water content had a much effect on the shear strength of the hydrophobic sandy soils. The shear strength index were decreased with the increasing of DMDCS volume by soil mass: the cohesion was declined rapidly from 19.6 kPa (no DMDCS) to 10.4 kPa (1% DMDCS) and slowly from 10.4 kPa (1% DMDCS) to 9.3 kPa (3% DMDCS). The internal friction angle was declined slowly from 16.2° (no DMDCS) to 11.8° (3% DMDCS). The cohesion was decreased with the increasing of water content: the cohesion was declined from 15.5 kPa (3% water content) to 7.5 kPa (13% water content) with 2% DMDCS and from 15 kPa (3% water content) to 5.2 kPa (13% water content) with 3% DMDCS respectively; the internal friction angle was increased from 12.7° (3% water content) to 15.2° (11% water content) with 2% DMDCS and from 11.7° (3% water content) to 14.6° (7% water content) with 3% DMDCS, then decreased to 13.9° (13% water content) with 2% DMDCS and 11.9° (13% water content) with 3% DMDCS respectively. 4) The Mohr-Coulomb strength criterion could also be adopted to describe the shear strength of hydrophobic mixed soils with different clay content. The cohesion was increased remarkably with the increasing of clay content. The cohesion of sandy soils without clay was 9.3 kPa, then suddenly increased to 27.2 kPa and 55.1 kPa mixed with 5% and 50% clay mass fraction, respectively. The internal friction angle was increased from 12.1° (5% clay mass fraction) to 16.2° (15% clay mass fraction), and then decreased to 9.7° (50% clay mass fraction). All the analysis could be beneficial to analyze the shear strength of hydrophobized soils and apply in engineering. [ABSTRACT FROM AUTHOR]

There are various methods for improving the engineering properties of weak soils among which the usage of chemical additives is one of the most important ones. Considering sepiolite as an environmental friendly material and its unique physiochemical characteristics, this substance has been used as an additive for soil improvement in this study. For this purpose, in addition to soil identification tests, in order to examine the effect of changes in the percentage of sepiolite additive, a set of tests has been done including Atterberg limits, modified compaction, uniaxial compressive strength, pH, direct shear and permeability test on sandy clay and clayey sand soils. Furthermore, scanning electron microscopy (SEM) and x-ray diffraction (XRD) tests have been performed to investigate the microstructure of non-stabilized and stabilized soil. According to the results, with increasing the additive percentage and the curing time, the uniaxial compressive strength of the soil increased. The uniaxial strength in the clayey sand soil rose up to six times larger than that of the initial strength of the soil. However, the maximum strength enhancement in the sandy clay soil was up to three times the initial value. Sepiolite (above 5%) has improved soil shear strength parameters including cohesion and internal friction angle. The increase in the additive content led to diminished permeability in soil. Further, the elevation of the sepiolite content in the soil resulted in enhanced liquid and plastic limits of soil. Microstructural investigations indicated that the reason of improvement in strength parameters of soil was the incidence of chemical reactions including ion exchange, flocculation and production of calcium-silicate-hydrate (CSH) and calcium-aluminate-hydrate (CAH) gels. Further, sepiolite fiber resulted in enhanced strength by filling the pores and void spaces of soil. • Sepiolite is an environmentally friendly material to stabilize the soils. • Increasing the sepiolite content during the curing time, increases UCS of the soil. • Sepiolite fibers act like bridges and connect different parts of soil. • CSH and CAH are products of chemical reactions between sepiolite and soil. [ABSTRACT FROM AUTHOR]

Abstract: Clay and organic matter, when incorporated together in a sandy soil, improved soil aggregation in association with both microbial activity and soil strength. Incorporation of clay into sandy agricultural soils in south-western Australia is a practice used to overcome water repellence, but the addition of high levels of clay can cause hardsetting. We investigated the extent to which addition of clay and organic matter would improve aggregate stability of a sandy agricultural soil from Meckering, Western Australia without negatively affecting soil strength. Four levels of subsoil clay and three levels of lucerne hay were compared in topsoil incubated for up to 42days at two temperatures. Addition of both clay and lucerne hay together increased stable aggregation and the longer the period of incubation, the greater the macroaggregate stability. A decrease in soil respiration associated with increasing level of clay added may be related to protection of organic matter. Soil strength increased when the amount of clay alone was increased, but addition of both clay and organic matter decreased soil strength. Soil amelioration with 5% clay and 0.8% organic matter was most effective at improving the stability of macroaggregates without hardsetting. The non-linear relationships observed demonstrate the importance of understanding interactions between biological and physical components of soil fertility in relation to the sustainability of land management practices. [Copyright &y& Elsevier]

Focuses on a study that discussed a four-parameter model that can represent the shear modulus factors and damping coefficients for granular soils. Information on nonlinear soil behavior; Effect of confining pressure on modulus and damping; Experimental data on cohesionless soils; Details on the MIT-S1 stress soil model for clays and sands.