| Ground fissures is a phenomena of surface rock or soil cracking,which can be caused the by climate dry,differential settlement,earthquake,tectonic movement,slope instability and so on.it brings A lot of harm to the society.The current large-scale physical model experiment system is without precedent in the field.A large physical model test system was established to monitor the development and evolution process of ground fissures based on the optical fiber sensing monitoring technology,such as FBG sensors,BOTDR,etc as the main monitoring device.The test system can achieve real-time monitoring of settlement deformation process caused by pumping.This system can be used to study on the earth fractures concerning its formation,evolution process,distribution laws,even the mechanisms as well as the partition of easy-happening area.This test provides a reference to using the optical fiber sensing technology to monitoring the evaluations of ground fissures.Difference settlement cracks experiment was carried out by the macroscopic model test and taking buried hill area as a typical research object.The experimental data of the ground water level,subsidence and differential settlement of the soil during the mining process showed that the settlement is closely related to the dropping of water level.The ground subsidence is affected by the water level.The higher the groundwater level is,and the quicker the reduction speed of groundwater level is,the more obvious the differential subsidence is.The study of the stress-strain field of soils shows that the tensile stress concentration of rock and soil is an important symbol to determine the development stage of ground fissures,and the tensile stress concentration area is the maximum probability of occurrence of ground fissures.During the evolution process of ground fissures in the buried hill area,not only the subsidence is obviously,but also the differential settlement is more prominent.Conclude that the location of the buried hill and the settlement curve of the surface as well as the distribution of ground fissures are basically the same.There is a corresponding relationship,which indicated that the differential settlement caused by groundwater extraction is the incentive for the formation of ground fissures and the shape of the buried hill to control the late evolution of fractures.The evolution and distribution of ground fissures was analyzed on the basis of the theoretical formula and probability integral method.The corresponding formula of probabilistic integral pumping sedimentation is deduced under the condition.The variation of differential settlement and surface curvature under the condition of buried hill is established.Through the research results,the ground fissures prone area is determined and development disk of ground fissures was evaluated.At the same time,the theory explains that the prone area of ground fissure is not at the top of buried hill in the engineering practice under the condition of bedrock buried hill.And the deduced formula is applied to the spatial prediction of subsidence development location of groundwater exploitation.Finally,from the micro perspective,the mechanism of ground fissures development is explained by using fracture mechanics.The morphology,distribution,width and length of the surface soil fissures were observed and studied.The variation of the corresponding parameters such as development of ground fissures,water content,matrix suction and fracture toughness were found out.The factors affecting the fracture characteristics of soil are obtained by studying the important parameters-fracture toughness in the research of fracture mechanics,which provide the theoretical basis for the study of ground fissures development and evolution.The fracture mechanics explanation is made on the development and evolution mechanism of surface dry shrinkage cracks,and concluded that: soil dehydration shrinkage is an important factor in surface soil to produce ground fissures. |
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