Study On The Moisture-heat Coupling Behavior Of Expansive Soil And The Mechanism Of Cut Slope Protection

In this thesis, expansive soil moisture-heat coupling behavior, disastrous mechanism and protection mechanism of cut slope is analyzed by the method of field test, lab experimentation and numerical simulation.Firstly, a large scale field test of expansive soil cut slope is carried out. Disastrous mechanism of the cut slope is analyzed based on weather observation, slope moisture-heat and permeability test, and deformation monitor. Working characteristic of vegetation and frame-anchor protection is also discussed. The results show that expansive soil engineering behavior is related with rainfall and evaporation closely. The change of water content is key factor to the slope deformation, and the change of temperature may accelerate the process. Therefore, the coupling action makes the slope unstable. Influence depth of water content increases with seasonal drying-wetting circulation, but the change of water content lags the heat. With vegetation covered, the fluctuate scope of moisture and heat is lessened, which prevent the developing of atmosphere influence depth. The deformation of slope is controlled by raining time, and only successive raining in certain intensity can induce large deformation. Swell-shrink behavior of expansive soil in the high weathering zone may make a great influence on the anchor bolt. When frame-anchor structure is built, the beam can confine the swelling of expansive soil, and keep the strength. At the same time, frame-anchor structure may release the swelling force, which contributes to the stability of slope protection system greatly.Secondly, by the method of lab experimentation moisture-heat coupling behavior of expansive soil is analyzed from the viewpoints of considering the effects of drying rate, wetting rate, hydration state and drying-wetting cyclic process. The results show that moisture and heat state has a great influence on expansive soil engineering behavior. Drying-wetting cyclic process makes soil more loose, lower strength, and higher permeability. A low drying rate induces a large shrinkage and air-entry value. A low wetting rate contributes a large swell deformation, and weakens the strength. During hydrating, the strength presents dynamic, and the state of long term and high temperature may lead to a low strength parameter.Thirdly, fissure feature is analyzed through the way of field test and lab experimentation combined with programmed software. The results show that statistic of two-value pixels and fractal dimension depicts the fissure in view of plane, and test of permeability and deformation modulus describes it from a spatial perspective.Then, working trait of expansive soil cut slope is analyzed by the method of numerical simulation considering expansive soil moisture-heat coupling behavior and fissure characteristic. And the vegetation protection mechanism is also studied taking into account of the mechanics characteristic and physiological trait. The results show that cut slope disastrous process correlates with expansive soil engineering behavior, and weather is a driving factor. The condition of seasonal drying-wetting circulation, evaporating process with a high humidity, and successive raining makes against the stability of expansive soil cut slope mostly. During raining root mechanics puts to effect primarily, and afterward, evaporation and transpiration puts into action which shortens the hydration time, prevents the strength decreased, reduces the weathering degree and is propitious to the long-term stability.Finally, protection characteristic of grouted rubble and frame-anchor structure is analyzed by means of numerical simulation. The results show that grouted rubble may keep the slope moisture steadily, lessen the influence caused by heat and difference in temperature, and prevent the developing of atmosphere influence depth. To frame-anchor structure that setting anchor bolts a free part in the high weathering zone can not only keep the safety coefficient of slope but also be in favor of the stability of anchor. Frame beam can let the deep soil bear the push force of slide mass, and then, make the surface stable. The distribute format of anchor axial force and frame beam bending moment is useful to design and optimization.