| It is inevitable to use underground cavern for refrigerated liquefied natural gas (LNG) storage in the world. But the very low temperature (-162℃) needed for LNG make a great challenge for building the storage cavern, so as to there isn't a successful engineering. Some researchers have carried out some preparatory study on the rock thermal and mechanical character and the construction of LNG storage cavern. For investigating the jointed rock mass surrounding the LNG storage cavern behavior during the freezing, the effect and action mechanism on rock (porous media) and crack (cranny media) were analyzed systemly when the temperature drop and freezing. Then the rock mass was taken as cranny media, the analysis method on thermo-mechanical coupling damage is established. The results of rock stress and stability during freezing can be provided scientific foundations to design and manage LNG storage cavern. The main contents and innovations can be concluded as follows:(1)The cracks appeared in wall and imbedded near the wall were simplified as a half infinite plane with a fringe crack and with a penetrated crack inside respectively for LNG storage cavern. To explore the action mechanism for crack fracture by temperature depress, the SIF at tip were be studied under many conditions by finite element method such as different parameters, different temperature boundary, different intensity and velocity of temperature change, and the angle of crack surface to the cavern wall.(2)The construction of LNG storage cavern was divided in two phases according as the concept model of building refrigerated LNG storage cavern which advantaged until now. The first phase, from drainage to excavation to freezing rock to before stopping drainage; the second phase, from stopping drainage to the ice ring formed and operating long term. And the damage analysis methods of thermo-mechanical coupling were proposed to each phase.(3)For the first phase, the water existed in unsaturated rock mass don't generate freezing heave when cooling, and ignore the freezing strength on the crack surface, the crack fractured model under complex stress state was be built base on the theory of geometry damage and the fracture and damage mechanics. Based on the area ratio between the contact area and the total area of crack defined as the pressure transfer rate, the thermal conduction model of rock mass was proposed according to the crack geometry and distribution both initial and fractured using the thermal resistance and thermal contact theory. Then the relation between the stress and thermal conduction of rock mass was also proposed through the pressure transfer rate. At last, the thermo-mechanical coupling damage model of rock mass was proposed under the action of temperature stress and initial stress during freezing. The program of transient temperature analysis, temperature stress and damage analysis coupling thermo-mechanical were developed using Fortran 90, and the fracture and damage of rock mass was studied by the developed program.(4)For the second phase, the drainage stopped, so the water begin to infiltrate the rock mass gradually which had been cooled and the ice ring formed. A fracture model of crack during freezing by ice pressure proposed base on the Walder model. The effect of restraining crack extend by the deadweight of rock mass, and the effect of promoting crack extend by water pressure were considered in the new model to meet the work condition after the ice ring formed , both of them had not been consider in Walder model. Then the crack fracture induced by the increasing ice pressure in the crack which developed by moisture transfer under temperature gradient. Finally, the analysis for crack fracture further by ice pressure were carried out from external factors such as the depth, temperature gradient, the wall temperature, coefficient of lateral pressure, the length and the obliquity of crack.
|
PDF Full Text Request