การศึกษาพฤติกรรมการเฉือนแบบไม่ระบายน้ำที่ขึ้นกับเวลาของดินเหนียวอ่อนทะเลภายใต้ภาระความร้อน : กรณีศึกษาดินเหนียวปากพนัง

Abstract

Pakphanang, Nakhon Si Thammarat province is located in the eastern coast of the southern of Thailand. The lowland plain is formed by deposition of soft marine clay. The past decade to the present, the city is the one of the rapid development. There are a large number of the constructions, houses, Industrial plants and nuclear power plants that could happen in the future. The heat from industries is transferred to the soil surrounding the building. Consequently, engineer must clearly understand the rate-dependent behavior of clay that is very important to predict soil behavior and design structure. Changes in soil engineering behavior because of the changing temperature affect the strength of clay. Clay is fine grain soil, cohensive, electrostatic attraction, double layer adsorb clay particle that relate to high plasticity and low permeability. Thus, shear strength behavior of clay depends on time-dependent behavior or viscosity of soil. Heat conduction causes pore water that is important to affect strength of clay. Since the permeability of clay is lower than its conductivity. Accordingly, this study focuses on investigating the time-dependent undrained shear behavior of marine clay under both thermal and mechanical loading. Isotropic consolidated undrained triaxial compression tests with controlled temperature and strained rates are carried out for this purpose. The shearing temperatures were 45 and 60 degrees Celsius in undrained heating condition. Shear rates were 0.02%, 0.075%, 1.0%, and 6.0% per minute. Soil behavior in term of the effect of the overconsolidation ratios (OCR) were 1, 2, 4 and 8 are also investigated. At the end of this paper, we will present a comparative study of the relationship between stress and strain, shear strength of soft clay at high temperature (drained heating and undrained heating) and room temperature. The test results were indicated that the Pakphanung marine clay is classified in high plasticity Organic clay, OH. Heat affects decreasing of plastic index and liquid limit. Noticeably, the higher the temperature, the lower the liquid limit, soil mass and also organic matter. Anyway, it did not affect molecular structure. The strain rates affect undrained shear behavior, showed that high strain rate, high shear strength for any OCR. Heat is a factor that stimulates the strength of Pakphanung clay, especially, in low strain rate. It depends on the ability to drain excess water from the soil mass. The drained heating causes the higher shear strength than the non-heating test. On the other hand, the heat conductivity is faster than the ability to drain excess pore pressure built by undrained heat, the soil strength will decrease. Heating causes the soil reaches the point of failure slightly faster than drained heating test. Stress and thermal affect the water pressure coefficient at the failure point (A) at low OCR, which is higher than high OCR. The drained heating test showed higher A than undrained heat test and room temperature test. Moreover, the temperature also contributes to the modulus of elasticity at the point of failure. Clearly, increase the modulus of elasticity secant. Drained heating tests give the highest state boundary. The slope of the critical state of undrained heat is lower than the drained heating and non-heating.