Research On The Theory And Engineering Application Of Seepage-stress Coupling Behavior Of Rock Mass Surrounding Tunnel Considering Residual Strength And Damage

This paper relies on the proposed Badaling Underground Project of Jingzhang inter-city railway. The content of the paper,which does a thorough research of the rock mass stress field-seepage field coupling theory which considering residual strength and damage, is based on detail rock mass structure survey statistics and large amount of single and triaxial stress-strain curve of rock. The achievement of the theory is applied to structure optimization and environmental impact assessment of Badaling Underground Project, and this article considers the Jianfengding tunnel on the Wuhan-Guangzhou high-speed railway when electricity pylons are present on the ground surface. The abstract of new research methods and research results are as follows:Characteristics of the residual strength of rock massThe residual strength of rock mass and the mechanical response of rock mass after peak strength are undoubtedly significant in tunnel and underground construction. This paper, from the following3aspects, conducts a study of residual strengthof rock mass:(1) the deformation and damage features of rock mass under uniaxial condition,(2) the residual strength of rock mass under tri-axial condition and (3) the numerical simulation of layered rock mass strength especially the influence of dip angle to the rock mass strength under uniaxial and tri-axial condition.Study on modified damage statistical constitutive model considering residual strengthThe increase amplitude of residual strength of rock is larger than the rock peak intensity of rock with the increase of confining pressure. Gradually, residual strength becomes the main factor of complete stress-strain curve of rock at the stage after peak intensity. Therefore, it’s necessary to consider the residual strength to modify the damage statistical constitutive model for Rock. Based on the strain strength theory and hypothesis of rock particles intensity obeying Weibull random distribution, a damage statistical constitutive model for rock under triaxial compression, which can describe the characteristics of rock post-peak softening, is established by adopting Hoek-Brown criterion and considering the residual strength to modify the damage parameter in this thesis. Then, all these model parameters analytic solutions are deduced according to the geometric features of rock complete stress-strain curve. On the basis of experimental results of granite specimens, the influences of Weibull distribution parameters on the rock damage constitutive model are studied. At the same time, the value of modified coefficient and the damage process of rock are discussed. Finally, the achieved theoretical curves by the damage model of rock under different confining pressure are comparatively analyzed with the conventional triaxial compression test results of four kinds of rock:porphyaceous adamellite, fine-particle marble, sandstone and silty mudstone.Fuzzy-synthetical evaluation on the system of geological strength indexWhen evaluating geologic intensity index, there are great randomness and fuzziness to confirm the value of its basic elements. As a consequence, it is difficult to accurately measure the impact of each influential factor. The fuzziness of the parameters of rock mass characteristics reflects its inherent uncertainty and the fuzzy mathematics theory provides strong measures to depict these characteristics. This article introduces the number of joint sets(Jn), joint spacing(l) and the integrity coefficient of rock mass(Kr) to describe the structure features of rock mass and introduces large-scale waviness(Jw), small-scale smoothness(Js) and Joint altered coefficient(Ja) to describe the conditions of structural planes. Then multifactor fuzzy-synthetical evaluation is applied to the system of geological strength index, meanwhile, analytic hierarchy process is adopted in determining the weight of each factor. As a result, the model of fuzzy-synthetical evaluation on the system of geological strength index is established. Practical project applications prove that this evaluation method has strong pertinence and high accuracy and it can organically combine geological surveys, experiment datum, statistics and expert opinions, so this evaluation method can decrease the subjectivity of researchers’ decisions. The method of fuzzy-synthetical evaluation on the system of geological strength index does provide a new approach to quantizing GSI system.Study on the seepage-stress coupling damage behavior of rockBased on some reasonable assumption, the seepage field and stress field equations have been derived through continuity equation, momentum conservation equation, rock statistical damage amending equation and some substantial equations. Then the seepage stress coupling damage behavior model is established in saturation state. According to some initial and boundary conditions of tunnel surrounding rock, the finite difference method is explored in seepage-stress coupling damage behavior model.Engineering applicationsIn order to access the environmental effects of the Badaling underground station project, numerical analysis for the stability of surrounding rock was done with fast Lagrangian analysis of continua in three-dimension(FLAC3D). Multiple factors were considered including surrounding rock classes, tunnel depths, groundwater tables, construction methods and initial supporting systems. The models are divided into four classes:the exclusion of underground water model, model with underground water seepage flow, model without underground water seepage flow, and a coupling analysis model with grouting reinforcement. According to the results of the displacement of rock mass, the pore pressure distribution and water gushing capacity, the significance, spatial distribution and long-term effects of environmental effects were discussed and the degree of influence were studied as well. The achieved results are successfully applied to the guidance of the tunnel construction for waterproofing of underground station. Furthermore, the study results can provide a theoretical basis for the design of tunnel and underground works in aquifer strata.The strata deformation of large section water-abundant soft rock shallow-buried tunnel under unsymmetrical pressure passing through existing structures would be effected by several factors. This article considers the Jianfengding tunnel on the Wuhan-Guangzhou high-speed railway when electricity pylons are present on the ground surface. First, the article describes the engineering measures needed as in-situ measured data to control large strata deformation. Second, statistical and theoretical analyses comprehensively studies the relationship between strata deformation and the impact of the existing building as affected by terrain condition, attitude of stratum, tunnelling construction, tunnel cross-hole construction, ground load, and ground collapse. Third, quantitative analysis is performed on strata deformation brought about by several critical factors and based on coupled fluid-mechanical numerical computation.