Research On The Distribution Rule Of The Shallow Crustal Geostress Field In The China Mainland And Engineering Disturbance Characteristics

Geostress is natural stress which hosted in the rock mass.It is one of most important data for the design and construction of the geological engineering,the evaluation index of geological environment and crustal stability.With the fast developing of transportation,water resources and hydropower,nuclear waste disposal, petroleum,mining and etc,in our country,the width and depth of human activity space is being more and more widely,and geostress is being more and more important for engineering and research.There are much geostress measured data and engineering examples in our country.In order to research the distribution rules of geostress field and the disturbed characteristics of construction in our country's mainland,based on the geological frame of our country and neighboring region,the mechanism solutions of earthquake focus and the characteristic of the geodetic deformation fields evolution,the characteristic of the tectonic stress field in our country was studied.By collecting vast geostress measured data,the distribution rules of measured geostress in our country was systematically studied.Based on the background of Three Gorges permanent lock slope and Dagangshan underground powerhouse,the characteristics of geostress field and disturb zones for high slope and large underground cavern were studied using the whole process numerical simulation. The main research work and achievement of this dissertation are as follows.(1) the advantages and disadvantages and the applicability of various geostress measured methods were summarized.From the view of the rock mass nonuniformity, measured method itself and geomechanics,the result difference among different measured methods were studied,which formed the scientific evaluation system of geostress measured methods and its results.(2) The preexisting fracture reopening test can determine fracture normal stress with high precision,and also can measure large scale three dimensional geostress.But if the space of the preexisting fracture was large,the stress gradient should be considered.Considering the stress gradient,the preexisting fracture hydraulic fracturing three dimensional geostress measured test was studied.Base on the distribution rule of the geostress with depth,the complete stress tensor expression of the linear stress gradient form of the vertical hole and the regional tectonic stress field were simplified,and the calculation process based on the genetic algorithm and the least square method were derived.It was first applied in the projects in our country. (3) From summarizing the characteristics of the formation and evolution of earths crust,the lithosphere structure,the distribution of fault systems and the plate activity in Chinese mainland and neighboring region,the nowadays characteristic of the geological condition in these regions were analyzed.Based on the existing research results of mechanism solutions of earthquake focus and geodetic deformation in Chinese mainland and neighboring region,the characteristic of nowadays tectonic stress field and the dynamics property in these regions were systemic studied.(4) Through collecting a vast amount of the measured geostress data and correlative materials,the distribution property of the measured stress orientation in Chinese mainland was analyzed.Through collecting the measured geostress data from about 400 drillings,a database was established.450 groups data with less topographical and local influence are selected as statistical samples,to study the distribution rule of the shallow crustal geostress in Chinese mainland.The dispersed point charts of the vertical stress,the maximum and the minimum horizontal principal stress varying with the depth were established.And the dispersed point charts of the ratios of the average horizontal principal stress and the vertical stress,the maximum and the minimum horizontal principal stress,the maximum and the minimum horizontal principal stress,the maximum horizontal principal stress and the vertical stress,the minimum horizontal principal stress and the vertical stress were also established.After corresponding statistical analysis,the distribution rules of the geostress in Chinese mainland were systemic studied.(5) According to their geological origins,111 groups of magmatic rocks data, 232 groups of sedimentary rocks data and 70 groups of metamorphic rocks data were selected from the established database of measured geostress data.The dispersed point charts of the geostress in the three types of rock varying with the depth were established,and the distribution rules of the geostress in different lithology were studied.Based on the measured geostress data with elastic modulus,the change rule of elastic modulus with depth was studied.The relationship between the rock strength, elastic modulus and the magnitude of geostress,and its impact on the maximum,the minimum horizontal principal stress and the vertical stress were studied.(6) The component of nowadays geostress were studied.According to the distribution rules of the geostress of depth and the influence rules of geostress by the pore water,temperature,geologic effect,the multi-factor geostress model with lateral restraint were discussed.(7) Referring to the Three Gorges Project and Dagangshan hydropower project as examples,the stress field of engineering areas was analyzed with mechanism solutions of earthquake focus,water system form distribution and fault striation. Based on the measured geostress in engineering areas and neighboring region, combining with the stress field back analysis of engineering areas,the distribution characteristics and the influencing factors of stress field of the big engineering areas were studied.From the geomechanics point of view,the relationship and difference between the regional tectonic and engineering areas stress field were analyzed.(8) Based on the background of Three Gorges permanent lock slope and Dagangshan underground powerhouse,using the whole process numerical simulation, the distribution characteristics and variation law of the stress field,deformation field and plastic zones of rock mass surrounding the large-scale underground cavern and the deep excavation and high rock slope were system studied.Based on the disturbed characteristics of the stress field after excavation,the stress field were divided into three zones,strong stress disturbed zones,weak stress disturbed zones and none stress disturbed zones.The change law of I₁,J₂,Lode parameters and the magnitude of the geostress of the surrounding rock were analyzed, and the methods for distinguish the disturbed zones and its engineering sense were also analyzed.