| In order to meet the needs of the energy strategy of China,a large number of water sealed caverns need to be built.Exploring the relevant technology of water sealed cavern has become the top priority of the national energy strategy,and carrying out the research on the relevant theory and engineering practice of water sealed cavern has also become a hot topic in the new era.However,in the pre-feasibility study stage of water sealed cavern,due to the lack of sufficient drilling data,the research of engineering often stays in the stage of investigation and theoretical analysis.In view of this background,this thesis takes an underground water sealed cavern project in Yantai,Shandong Province as an example,and puts forward a method of in-depth research on the water sealed cavern in the pre-feasibility study stage,combining with field survey,geological survey,in-situ test,indoor test,numerical simulation and other technical means.The underground water sealed cavern project in Yantai,Shandong Province was taken as the example.Combined the field survey work carried out in the target area with a small amount of borehole information,the three-dimensional spatial distribution characteristics of rock mass discontinuities were studied,in the pre-feasibility study stage,due to the lack of borehole information.Then,by analyzing the information characteristics of discontinuities in the borehole,a comprehensive model of hydraulic parameters based on the parameters of discontinuities was established.Through the numerical simulation software,combined with the statistical results of structural plane,the overall stability of surrounding rock and local block stability were analyzed.By using FEFLOW software,the water seal conditions of water sealed caverns under different conditions were analyzed.This method could become a general research method in the pre-feasibility study stage and even in the follow-up stage.The main conclusions are as follows:(1)Combined with field survey and indoor borehole image interpretation,the outcrops,air raid shelters and structural planes in boreholes were counted,and the collected structural plane sample data were screened and grouped.In view of the inconsistent sampling accuracy of field outcrops,air raid shelters and internal fractures in boreholes,the tiny fractures in boreholes were deleted by controlling the linear density.According to the statistical results of discontinuities at different sampling points,the corresponding dominant discontinuities were selected and grouped on the needs of 3D discontinuity network modeling.Then,the 3D network model of structural plane was established by using random function through AUTOCAD.And based on the 3D network model,it was proposed that the minimum and maximum area of structural plane density should be avoided in axis selection,that was,the two axis strike intervals of 30°to 50°and 120°to 150°should be excluded.Using the virtual drilling of the longitudinal section of the three-dimensional network model,the quality of the rock mass was evaluated.The results showed that the large structural plane in this area was extremely undeveloped,and the rock mass was complete with good quality.It was an ideal site selection area for large water sealed caverns.Finally,the traditional BQ method was used to classify the surrounding rock,and the consistent rock quality evaluation conclusion given in the three-dimensional network model was obtained.This method could be used to establish a three-dimensional network model by statistical fracture discontinuities,and to form a preliminary understanding of the distribution characteristics of discontinuities in the field with a small number of boreholes in the early stage,which was conducive to the subsequent work of surrounding rock stability and water seal condition analysis.(2)By analyzing the theory of permeability coefficient of fractured rock mass,the structural plane parameters,such as roughness,gap width and dip angle,which were suitable for establishing the comprehensive model were selected.The relevant information of fractures in the borehole was extracted through drilling video.Combined with Barton's empirical formula,the comprehensive model of hydraulic parameters based on structural plane parameters was established.By comparing the model calculation trend,indoor test trend and in-situ test trend of the relationship curve between permeability coefficient and buried depth,it was concluded that the model calculation trend could relatively well reflect the results of in-situ test.And the difference between outdoor and indoor fracture seepage curve mainly came from the sample preparation and test conditions.When the water pressure test was difficult to be carried out in some certain section of the borehole,the calculation results of the model could be used to replace the water pressure test,or it could be used to reduce the number of water pressure tests to decrease the cost,and to help to establish the hydrogeological model.(3)The three-dimensional geological model of water sealed cavern was established through ANSYS software,and the stability of surrounding rock with or without cracks passing through the cavern area was analyzed.According to the results of the overall stability analysis of the cavern,the plastic zones around the surrounding rock of the cavern were mainly concentrated on both walls of the cavern,so it was necessary to carry out the local block stability analysis for this situation.The numerical simulation results showed that the stress field,the displacement field and plastic zone of the surrounding rock in the cavern area changed little,and the surrounding rock was considered with good stability.The stability change of surrounding rock with cracks was mainly reflected in the stress,and due to the particularity of fracture tendency,the change of X direction was relatively obvious.Because the total stress change was not large,it was considered that the stability of cavern was good as that without cracks.Based on the analysis of the key blocks,through UNWEDGE software,the key blocks were determined by using the previous statistical results of structural planes and the following conclusions were obtained:(1)the volume of a key block was large at the left vault of the combination of2,3,4 structural planes in area N,and its falling off created a certain threat to the construction;(2)the volume of a key block at the left vault of the combination of 2,3,4structural planes in area S was largest,which is 4 m~3.It would pose a great threat to the safety of personnel and equipment in the construction process.(4)According to the geological model established before and the stratification of permeability coefficient of surrounding rock determined by the hydraulic parameter comprehensive model based on structural plane parameters,the hydrogeological model of water sealed cavern was established by using FEFLOW software,and the water seal conditions under different conditions was analyzed,such as whether there were cracks passing through the cavern area,whether there was water curtain layout,and whether excavation or operation was different.The conclusions are as follows:(1)the water curtain system should be arranged before the excavation to ensure the water seal condition around the surrounding rock of the cavern,and the water curtain system must be arranged during the operation process to maintain the safe water seal condition;(2)the water seal property of large cracks would be greatly affected when they pass through the cavern area,so it was necessary to block the large cracks in time. |
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