Effective Stress and Compressibility of Unsaturated Clayey Soil under Drying and Wetting Cycles

Naturally, soil moisture reduces during dry seasons when the soil is in drying state; while it increases during wet seasons when the soil is in wetting state. Previous studies have shown that for an unsaturated soil sample, soil-water characteristic curves (SWCCs) do not match in wetting and drying paths. The differences between wetting and drying paths are called the hydraulic hysteresis. The hydraulic hysteresis plays an important role in mechanical properties of soil such as shear strength, volume change, and settlement. The objective of this research is to study the effects of drying and wetting on the effective stress and compressibility of unsaturated clayey fine-grained soils. To this end, saturated and unsaturated triaxial tests were performed on the soil samples under various normal mean stresses, and matrix suctions in drying and wetting paths. It was found that soil samples bear higher levels of effective stress in the drying path than the wetting path under a same level of suction. The attained values of effective stress parameter (χ) showed that the Bishop’s effective stress parameter (χ = Sr) is not properly applicable for the clayey soil. Moreover, the resulting loading-collapse curve (LC) revealed that the effective pre-consolidation pressure in the drying and wetting stages changed even with same degrees of matrix suction

Temperature effect on compression and collapsibility of residual granitic soil

U ovom se radu istražuje utjecaj temperaturnih promjena na indeks stišljivosti i potencijal kolapsibilnosti rezidualnog granitnog tla na koje se često nailazi u Maleziji. Zbijeno tlo analizirano je pomoću modificiranog edometra s kontrolom temperature. Dvije serije uzoraka tla s raznim vrijednostima suhe gustoće ispitane su pri temperaturama od 27, 40 i 60°C. Rezultati ispitivanja pokazuju da vrijednost indeksa stišljivosti ne ovisi o temperaturi. S druge strane, grijanje dovodi do smanjenja potencijala kolapsibilnosti, a ta je pojava izraženija pri niskim vrijednostima suhe gustoće.This research aims to investigate the effect of temperature changes on the compression index and collapse potential of the residual granitic soil that is widely encountered in Malaysia. An experimental study was conducted on the compacted soil using a modified temperature-controlled oedometer. Temperatures of 27, 40, and 60 ºC were applied on two series of soil specimens with different values of dry density. Experimental results showed that the value of compression index is independent of temperature. On the other hand, heating caused a reduction in collapse potential, which was more pronounced at low dry density

Collapse/swell potential of residual laterite soil due to wetting and drying-wetting cycles

Lack of consideration in the soil behaviors related to drying and wetting phenomenon namely volume change and collapsibility may cause damages to foundations, buildings, and other structures. This research reports an experimental work carried out to examine the collapsibility behavior of residual laterite soils under cyclic drying and wetting process, different initial water contents and dry densities. A modified oedometer was employed to perform air-drying and wetting cycle on the soil samples. The results showed that the soil collapsed upon wetting at a constant vertical stress. The collapse potential of the soil increased initially to a maximum value with increasing vertical stress and then decreased at higher levels of vertical stress. The drying-wetting cycles caused a reduction in void ratio and an increase in feasible cementation bounds of the residual laterite soil. As a result, the collapse potential diminished and the swell potential slightly increased. Yet, the soil with high dry density not only did not produce desirable results in reducing the collapsibility, but also slightly increase the soil swelling under the wetting-drying cycles

Foundation size effect on modulus of subgrade reaction on sandy soils

Winkler model is one of the most popular models in determining the modulus of sub grade reaction. In this model the sub grade soil is assumed to behave like infinite number of linear elastic springs. The stiffness of these springs is named as the modulus of sub grade reaction. This modulus is dependent to some parameters like soil type, size, shape, depth and type of foundation. The direct method for estimating the modulus of sub grade reaction is plate load test that is done with 30-100 cm diameter circular plate or equivalent rectangular plate. Afterward, we have to extrapolate the test value for exact foundation. In the practical design procedure, Terzaghi's equation is usually used to determine the modulus of sub grade reaction for actual foundation, but there are some uncertainties in utilizing such equation. In this paper the size effect of foundation on sandy sub grade with use of finite element software (Plaxis) is proposed to investigate the validation of Terzaghi's formula on determination of sub grade reaction modulus. Also the comparison between Vesic's equation, Terzaghi's one and obtained results are presented