| Principle of underground water sealed storage cavern is put forward in the early1930s. So far, many countries have successfully built more than60underground water sealed storage caverns, but China still has not grasped the core technology of it mainly because foreign countries keep their technique secret. Sweden, France and other foreign companies dominated and build underground water sealed liquefied petroleum gas storage caverns in Shantou, Ningbo, Zhuhai and Huangdao, but they don’t disclose the core technology. Therefore, we are still in the stage of groping and testing the construction technology of underground water sealed storage caverns. The knowledge of deformation-failure characteristics of surrounding rock is not enough and the theories and methods of controlling the deformation and failure is no mature. As we are in the boom of underground construction for energy storage, it has important theoretical and engineering significance to have research on the deformation-failure mechanism and bolt-shotcrete support of surrounding rock.The underground water sealed rock caverns make use of the feature that oil or gas will not mix with water. Then we can control the water pressure of surrounding rock in the caverns reasonably, and make it always greater than the pressure of the oil or saturated vapor in the caverns. Therefore, the type of this engineering include several of special properties, such as the water curtain system must keep injecting high-pressure water continuously, the high pressure water infiltrates into the rock of the cave, the pressure of liquefied petroleum gas changed frequently by the normal exhaust and storage activities, and so on. And all of these engineering properties determined that, the construction of the cavern cannot copy other existing underground engineering experience and technology, but must research the properties separately on the basis of its geological environmental conditions. Because of the long-term effects of water curtain system, the coupling water-rock interaction needs to be considered in the stability analysis. Caverns always be constructed in the place where the rock is hard, and the discontinuity is less-developed. The discontinuity surface generally has no fillings and degree of weathering is low. So, chemical action between the rock and groundwater is minor, and the water exchanges between the rock and fracture is very little, which determine that water-rock interactions mainly for mechanical coupling between seepage in the fracture and rock stress. The discontinuities always have low surface roughness; the dilatancy of rock mass is unobvious, so the main factors that affecting the characteristics of seepage is its normal stress. The underground water-sealed rock caverns are generally constructed in shallow state. This is because, when the engineers designed the depth of caverns, in the considering of the seal principle and economy, it is reasonable that height difference between the water table and the bottom surface of caverns is greater than the saturated vapor pressure of storage medium plus a safety height. Therefore, surrounding rock in the caverns generally has a low strength, and its deformation and failure mode is mainly controlled by the rock structure. And these engineering properties had mentioned above also determined that the support programs are different from other underground engineering. It needs to be studied more directed and reasonable, which can provide more theories and basis to support its safety and economy.The paper analyzes the underground water sealed liquefied petroleum gas storage caverns in Wanhua, Yantai qualitatively and quantificationally by combining testing, monitoring and theoretical analysis and have research on the deformation-failure mechanism and bolt shotcrete support of the surrounding rock. The paper focuses on the interaction between groundwater, rock mass and supporting structure and the resultant deformation and destruction law of rock mass. The researches mainly include:the network model of fractured rock mass is built and characterized by computer technology; the relationship between equivalent hydraulic aperture and normal stress of discontinuities in the caverns area is established based on the hydrology test, in-situ stress tests and borehole image. The deformation-failure modes of surrounding rock is discussed and the deformation-failure mechanism is revealed based on the field monitoring and numerical simulation. The scheme of bolt-shotcrete support is optimized through the Q system and the supporting effect is evaluated with the field monitoring data. The main works accomplished are as follows:(1) Based on the principle of borehole camera technology, the determination processes for discontinuity orientations in inclined boreholes were described and derived in detail in this paper. With the drilled orifice circle centre as the origin, the left-handed Cartesian coordinate system was constructed and the precise analytic formulas for discontinuities orientation in inclined borehole were achieved. Based on the principle of borehole camera technology, the validity of analytic formulas and program were verified. In addition, the PVC pipe experiments were conducted to examine the reliability of borehole camera technology for measurement of discontinuity orientation. Results show that:(1) for inclined PVC pipe with trend of270°and plunge of25°, the degree of reliability of discontinuity orientation is0.10; while inclined PVC pipe with trend of176°and plunge of60°, the degree of reliability of discontinuity orientation is 0.67. The difference of pipe plunge results in the reliability differences of discontinuities orientation.(2) The reliability grade of discontinuity orientation should be high for general rock engineering, so that the plunge of inclined boreholes is not less than71°should be needed.(2) Based on iterative self-organizing data analysis technique algorithm, a discontinuity grouping model named self-organizing fuzzy clustering is established. This model can consider multiple indexes of discontinuity quantitative description and their weighting. For details of this model, firstly iterative self-organizing data analysis technique algorithm was improved according to basic requirements of discontinuities data treatment, secondly fuzzy membership and fuzzy weighted index were added to the improved algorithm, thirdly index weighting was included in Euclidean distance equation and standard deviation equation. Based on space architecture relation, calculation formula of discontinuities spacing is given under the grouping model.(3) Based on pseudo-random number generated by Excel and three-dimensional discontinuity disc modeled with AutoCAD, three-dimensional network simulation of discon-tinueities is successfully realized. The paper point out that structural homogeneity of rock mass and network model checking based on engineering geological conditions and the measured data are significant. When three-dimensional network simulation of discontinuities is checked through the measured data, the specific location of discontinuity could not be confirmed but some statistical parameters might contrast. This is because that three-dimensional network simulation of discontinuities is not a real scene but only the simulation of statistical sense. The latter error recognition is the root of the abuse of three-dimensional network simulation of discontinuities.(4) Because of the limitation of computer hardware, the large number of discontinuities model cannot be operated generally or the result is unreliable owing to the numerical truncation error. So the short and intensive discontinuities are eliminated by setting the diameter threshold value, occurrence difference threshold and center distance threshold. After the discrete element model was established, small blocks that are easy to affect the calculation rate and deformity are cut off by setting the volume threshold. Finally, the same discontinuity is given with different parameters regards to characterize the virtual and real parts. Thus, the discrete element representation of rock mass structure model based on stochastic simulation comes true successfully. This exchange algorithm is programmed through FISH language in3DEC software.(5) A discontinuity equivalent hydraulic aperture inversion method is put forward. The method is based on the borehole image, water pressure test in borehole and permeability tensor theory calculation. Firstly, based on the trial method, the reduction coefficient is confirmed and the equivalent hydraulic of the structure in aperture water pressure test section is preliminarily determined. Then genetic algorithm is used to optimize equivalent hydraulic aperture with greater uncertainty, to obtain more accurate numerical. The fracture network calculation method has calculated taking the single structure as a unit but without discontinuity set, it can improve the reliability of the results. The method can simultaneously inverse a large number of discontinuity equivalent hydraulic aperture.(6) Analyses of statistics show that:borehole pressure water experimental section that average aperture is70to100times as the initial equivalent hydraulics aperture counts77.5%in the overall experimental sections. It means that geometrical average aperture is greatly different from equivalent hydraulics aperture. While studying rock hydraulics and fractured rock masses, it is essential to notice this difference. The court construct surface that equivalent hydraulics aperture distributed from10um to100um counts99%in all, and they gathered between lOum to45um, which almost counts65%in all. When normal stress of discontinuity is larger than7MPa, the relationship between equivalent hydraulics aperture and normal stress is not that obvious, while it is smaller than7MPa, equivalent hydraulics aperture will be obviously decreased as normal stress increased.(7) The estimating formula of mechanics parameters for rock mass with different Q value is given, which is based on the relation of GSI and Q value, Hock-Brown failure criterion and rock mechanics test. Taking Q value is4as an example; test is carried out with monitoring data. The result shows that the method is rational and reliable. The discontinuity mechanics parameters are obtained from direct shear test and empirical formula. Taking cavern group consists of shaft, water curtain tunnel, branch tunnels and main cavern as study object, considering rock mass Q value is4and ignoring water-rock coupling, the numerical simulation is carried out using3DEC software. Result shows that the distance between each underground structure is reasonable, there is no influence with each other, and the global deformation-failure mechanism is controlled by the secondary stress and the displacement and plastic zone is small.(8) Taking the main rock cavern as study object, considering fracture groundwater mechanics coupling, the deformation-failure mechanism of surrounding rock is studied by3DEC numerical simulation. Results show that the reason of the unstable block on the left shoulder of main rock cavern is the combination of discontinuity and the excavation surface. The flow field in the unstable block is different with others obviously, the flux and flow rate increased rapidly. This is because the increase of permeability coefficient increase caused by the tensile stress which expands the equivalent hydraulics aperture. Meanwhile, the zero water pressure on the excavation surface induces the increase the hydraulic gradient. Through the overall study, the appearance of the unstable block is a local failure, the main reason is the advantageous combination of discontinuities, and the subsidiarity reason is the groundwater which promote and acceleration the failure. It is very necessary to grout appropriately for cutting off groundwater while controlling the unstable block.(9) Based on the construction condition of underground water sealed liquefied petroleum gas storage cavern, the bolt-shotcrete parameters are get through Q system initially. Then these parameters are checked by3DEC software from the aspects of continuous and discontinuous surrounding rock. Results show that:(1) when surrounding rock is continuous, the bolt-shotcrete support has an obvious effect to the displacement of surrounding rock, and the bolt-shotcrete parameters is safe and reasonable;(2) when surrounding rock is discontinuous, the bolt-shotcrete support fails due to the local instability blocks;(3) the support object of Q system does not include local instability block, so it is necessary to support design combined with discrete element numerical simulation, and it is important to discriminate local instability problems during construction stage. (10) Based on bolt-shotcrete parameters calculated from Q system, the optimization study is carried out. Bolt longitudinal spacing, length and shotcrete thickness is chosen as optimization indices. Then surrounding rock displacement, shotcrete stress, cable force and node failure situation is chosen as evaluation indices. The numerical simulation program can be get based on orthogonal design. The nonlinear relationship between evaluation indices and optimization indices is constructed through evolution neural network. In determining the reasonable value of supporting safety evaluation on the basis of shotcrete optimization indices, combined with the actual progress of the project, show that the optimized parameters for a particular section of the Q value is safty, reliable, and can provide for similar projects based on the reference.The following innovation points can be reported for the conducted study:(1) According to the current study situation that borehole camera technology only applied to the vertical boreholes, the determination processes for discontinuity orientations in inclined bore-holes were described and derived in detail in this paper based on the principle of borehole camera technology. In addition, the PVC pipe experiments were conducted to examine the reliability of borehole camera technology for measurement of discontinuity orientation. Based on iterative self-organizing data analysis technique algorithm, a discontinuity grouping model named self-organizing fuzzy clustering is established. This model can consider multiple indexes of discontinuity quantitative description and their weighting. These methods greatly expanded the investigation and analysis of the structural planes.(2) In sight of the applications of three-dimensional network simulation of discontinuity only stay in the geometric hierarchy, so the distinct element algorithm is introduced based on3EDC and FISH language, which can make the three-dimensional network simulation combine with mechanical calculation. The algorithm is needless to build fictitious discontinuity and improves the computational efficiency.(3) The equivalent hydraulic aperture of discontinuity is difficult to determine in engineering. Based on borehole image technology and water pressure test in borehole, the inversion method of equivalent hydraulic aperture is proposed combined with the test algorithm and genetic algorithm, which can invert hydraulic aperture of discontinuity in the whole water pressure test period. The relation between equivalent hydraulic aperture and normal stress is summarized through regression analysis of in-situ stress, which lay a strong foundation for the further study on coupling of flow-stress.(4) The study on rock deformation and failure mechanism of underground water sealed caverns is less and the conclusion is unsystematic result from rare engineering project. The rock deformation and failure mechanism is raised according to cavities unit model and the main cavity in consideration of coupling of flow-stress, through a large number of discrete element numerical calculation, in combination with field monitoring data, in which the secondary stress, rock mass structure, and groundwater are distinguished in the rock deformation and failure process.(5) The parameter optimization of bolt-shotcrete support is easily to fall into local optimal value in past. The new parameter design method of bolt-shotcrete support is proposed, which is based on Q system for choice of primary parameters, orthogonal design and combination of evolutionary neural network and numerical calculation. This kind of method is tend to apply in engineering and has good universality in the project. |
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