| Land subsidence is one of the worldwide geological problems that its evolution will cause serious geological disaster. The large numbers of extraction of underground resources which were water, oil, gas and coal, and the disorder underground engineering created the 90% land subsidence, for instance, the overrated underground water extraction caused strata settlement, civil engineering(like subway construction) caused foundation base subsidence and mining caused strata movement or surface subsidence. The vertical shaft developing was the main development method of the mining area in eastern China, the shaft passed through the thick quaternary unconsolidated layer, and the vertical shaft deformation and broken became the major calamity of the mining safety production in these districts, and this type of geological disaster had a strong threat to mining safety production. The root cause of the vertical shaft wall fracture was the water loss compression subsidence of the thick quaternary unconsolidated layer, its subsidence deformation prevention was critical to predict the shaft repeat fracture. Application of fiber optic sensing technology in subsidence monitoring of unconsolidated layer made the unconsolidated layer deformation behavior research, unconsolidated layer subsidence deformation calculation and prediction possible. The fiber optic sensing technology and the research of unconsolidated layer subsidence deformation mechanism and behavior provided the theoretical foundation and the engineering basis to the thick quaternary unconsolidated layer subsidence deformation monitoring caused by water loss in eastern China mining area, it had important significance to prevent unconsolidated layer subsidence deformation and predict the shaft fracture.This dissertation aimed at the compression subsidence caused by water loss at the bottom of the thick quaternary unconsolidated layer in eastern China mining area, combined with the geological structure, the dynamic hydrological characteristics and the unconsolidated layer subsidence monitoring technology based on fiber optic sensing, the rheological characteristics of different lithological soils of unconsolidated layer, the subsidence mechanism and the unconsolidated layer deformation behavior have been studied at several aspects which summarized below.(1) The unconsolidated layer deformation mechanism was studied by high pressure consolidation test and sand particle size screening test, three kinds of lithology soils of thick quaternary unconsolidated layer in eastern China mining area were tested, which were sand soil, clay soil and sandy clay soil. In this paper, the creep properties of unconsolidated layer in eastern China mining area were studied, and the stress-strain-time nonlinear rheological model of unconsolidated layer at different lithology was built. The tests showed that the unconsolidated layer had instantaneous elasticity and viscosity properties, the sand soil had the larger proportion of elastic deformation in a single load, then the sandy clay soil, the clay soil had the smaller elastic deformation, and the sandy clay soil had an obvious elastic aftereffect. The effect of different stress history on rheology property was investigated, the deformation rate of soil mass at a load bellowed the average stress level was less than it at a load above the average stress level. The subsidence deformation mechanism of the unconsolidated layer in eastern China mining area was studied, which showed that the particles breakage and particles slippage have been impacting the subsidence deformation together.(2) The physical model test device based on fiber optic sensing technology for unconsolidated layer subsidence deformation monitoring was designed and manufactured independently. The model test of thick quaternary unconsolidated layer subsidence deformation monitoring based on distributed fiber optic sensing technology was implemented. Deformation behaviors of the thick quaternary unconsolidated layer under water injection condition were studied, and the associated parameter to retarding the unconsolidated layer subsidence was obtained too. Then the deformation behaviors of the bottom of thick quaternary unconsolidated layer under water loss condition were studied. The relations of the effective stress increment and strain under water loss and water injection of unconsolidated layer were researched. An experienced prediction model of unconsolidated layer subsidence was built based on nonlinear rheology constitutive model and strain model, which completed the expression of unconsolidated layer subsidence deformation behaviors in eastern China mining area which was based on the water level lowering-settlement experiential fitting model. Experimental studies showed that: water injection effectively improved the stress state of unconsolidated layer; the influent height of the upside of the water injection layer was about 0.024 times as the water head. The water injection depth would be under the compression layer. The stress state changed from tensile stress to compressive stress when the unconsolidated layer loss water, the vertically compress extended from the lower group aquifer to the middle group aquiclude with the water level continually decreasing, and there would generate tensile stress concentration areas at the upper water injection layers and the junctions of unconsolidated layers in different lithology. The stress state of unconsolidated layer water injection process met an elastic-elastoplastic-plastic, 1-2 kPa stress relaxation presented at the initial stage of the water loss process.(3) The strain transfer function of embedded fiber Bragg grating sensors for unconsolidated layer settlement deformation detector was theoretically elicited, and the temperature compensation method of fiber Bragg grating sensing monitoring was investigated by field test. In this paper, the assumed condition of embedded fiber Bragg grating sensor was presented, and a new mathematical model of strain transferring of the unconsolidated layer and FBG sensors which considered borehole radius and elasticity modulus of the borehole sealing materials, and the relations of strain transfer with borehole radius and borehole sealing material was proposed. It shows that the strain transfer rate would be higher when the elasticity modulus was in the range of 8-15 GPa.(4) A field test was carried out based on former theoretical and experimental studies, and the unconsolidated layer subsidence deformation in eastern China mining area was investigated. The relation of unconsolidated layer strain and time was analyzed, the dynamic water level and the corresponding layer strain changes was studied. Characteristics of unconsolidated layer vertical settlements were researched, the compressive strain increased when the unconsolidated layer was near the bed rock. Determination and prediction method of main compressive layer in thick quaternary unconsolidated layer was put forwarded, it would comprehensively considered the thickness, deformation rate and unit deformation value, the determination should on the basis standard of contribution ratio that the layer subsidence to the total subsidence. The results showed that the middle group sandy clay layer was at a long-term creep deformation stage, little water level rise could not offset the long-term creep deformation. The lower group clay soil layer and the lower segment of middle group sandy clay soil layer were the main compressive layer at the present stage, the research extended the cognition that the thick quaternary unconsolidated layer subsidence in eastern China mining area occurred in the lower group or lower bottom group, and the impacts of middle group subsidence to the shaft fracture should be taken serious. The lower segment sandy clay in middle group and lower bottom layer of the thick unconsolidated would be the main subsidence layer, the shaft depth corresponding to unconsolidated layer which the creep deformation occurred should be paid attention to and enhance the deformation monitoring and maintaining of these vertical shafts. |
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