The Characteristic Of Unsaturated Soil Induced By The Extraction Of Geothermal Energy Resource

Geothermal energy is a new green energy sources, it developed word widely in recent years. In general, the geothermal energy is always abstracted through geothermal holes and energy piles. According to some researchers’ results and many engineering monitoring, it shows that the running of the system which changed the surrounding temperature and humidity field, it can result in inducing the soil unsaturated. It is well known that the soil can easily influenced by the atmosphere. In fact, our real engineering construction is under the unsaturated environment. However, the study of unsaturated soil is not easy and rare, it is necessary to explore the characteristic of the change and to understand its principle.The method of study on the unsaturated soil is soil experiments. The experiments and mainline of this paper are all serving for the suction. The main study methods is the laboratory experiments which includes the controlled suction test by polyethylene glycol (PEG), dynamic vapor sorption (DVS) test, mercury intrusion porosimetry (MIP) test and the suction controlled oedometer test. The test materials used in these experiments are the unsaturated soil which has three main conditions (with optimum water content, the wet side of the optimum water content and the dry side of the optimum water content).The state of the suction main infers to low suction (100KPa,200 KPa,400 KPa and 800 KPa) and high suction(1.5MPa,3MPa,6MPa,8MPa and 9MPa). The object of the paper is to understand the performance of the compacted clay under these different conditions.The main study results:the changing law of the soil water characteristic curve (SWCC) under different initial water content, the drying and wetting line and its mass changing under different suction, with the suction increasing, the water content decreased, the void ration decreased, the degree of saturation decreased; the characteristic of cumulative pore size distribution curves and pore size density function curves under different water content and suction, it shows that the soil has two advantage pore size 13nm and 3μm, with the increasing of suction,the bigger advantage pore size is degreasing; the deformation characteristic of the unsaturated soil under low and high suction, then compared with the saturated clay.The results highly proofed that suction is one of the most parameters which has a strong influence on the performance of the unsaturated soils. It has a close relation with its mechanical characteristic, also it can change the unsaturated soil’s microstructure and make a new distribution of the inter-aggregate and intra-aggregate.