Expansive Soil Subgrade Water Damage To The Mechanism Of Action And Prevention Measures

Expansive soil, formed in natural geologic processes and composed of a great deal of fissure, is of remarkable shrink-swell properties. It is the highly dispersive and plastic clay which is crannied and its volume will expand (or shrink) and its swelling and shrinkage will occur alternately when its moisture content increases (or decreases). It has consolidation and fissure characteristic and also has a wide-ranging Distribution. Expansive soil causes much damage to the engineering, but because it is complex variable, and we especial to water-destroyed mechanism. This paper we give a theoretical considerations and test on the water-destroyed mechanism. First, we research on the unsaturated behavior of the expansive soil. Based on the Chang-Zhang highway engineering and Nan-You highway engineering, we give both laboratory test and theory research on the water-destroyed mechanism, proposing and implementing the measure to prevention and treatment of water-damage. Some original conclusion were obtained as follows:1. Water-destroyed mechanism of expansive soil roadbed: Giving a research on the moisture migration of expansive soil, the type of water-destroyed of expansive soil roadbed, formation analysis for landslide, characteristic of landslide and mechanism of instability. Researching on the water-destroyed mechanism which include slaking-destroyed mechanism, weathering-destroyed mechanism, surface runoff and erosion-destroyed mechanism. And also research on slope stability method.2. Fundamental properties of unsaturated soil. Giving a research on the suction characteristics, stress properties, Strength properties, permeability and deformation behavior of the unsaturated soil. Researching on the problem of unsaturated soil mechanics, which includethe rule between suction and water content, constitutional relationship of unsaturated soil, the rule of moisture migration of unsaturated soil, suction and the key mechanics questions in it, problem between saturation and shear strength indices, problem of measurement of matrix suction in unsaturated soil. And based on it, giving a research on the characteristic of unsaturated soil.3. Simulated experiments on the water-destroyed mechanism of expansive soil roadbed: we have done 8 groups of simulated experiments, researched on the water-destroyed mechanism of expansive soil under dry-wet circulation circumstance.4. Measure to prevention and treatment of water-damage of expansive soil roadbed: Water proofing and moisture preserving treatment as follows: Using geo-membrane, unexpansive soil, stabilized expansive soil and totally enclosed expansive clay. Type of retaining structure as follows: three-dimensional vegetation net grass-planting revetment in the banks of expressway, supporting blind drain+ reinforced wall in cutting slope of subgrade safeguard, application of sand-free poor concrete with macropore blind drain, gravity earth-retaining wall, antislide pile, cruciform anchor frame and anchor frame beam of subgrade safeguard. Also using design techniques, construction measures, improving clay to prevent and treat water-damage of expansive soil roadbed5. The application of prevention and treatment of water-damage of expansive soil roadbed in engineering: Cutting slope treatment project for expansive soil on Nan-You highway as follows: Using geogrids-reinforced retaining wall in the engineering, Using multistage strengthening in the section of K138+440～K138+750; Using supporting blind drain+ reinforced wall in the section of K138+440～K138+750, Using anchor frame in the section of K139+100～K139+400. The measures of strengthening in Chang-Zhang expansive soil roadbed as follows: Using weak expansive soil in the section of K85+900～K85+960, Using improvement of expansive soil in the section of K85+960～K86+020, Using reinforced expansive soil in the section of K86+020～K86+080.