Results Of Rock Stress Measurements And Engineering Significance Of Song-shu-yuan Tunnel In New Railway From Dali To Li-jiang In Yun-nan Province

Rock stress state in situ consists in stratum and not in disturbance band, also called initial stress of rock mass, utter stress or former rock stress, and called in-situ stress in engineering, too. It is the essential power that arouses distortion and destroy in railway, highway, mining, water resources and hydropower, civil engineering, military affairs and other underground engineering or excavated geotechnical engineering in the open air. And it is the necessary premises for making sure mechanical property of engineering rock mass, analyzing stability of wall rock, scientific designing and decision-making for excavated geotechnical engineering. Results of rock stress measurements can tell the size and direction in the rock mass, thereby supply gist for analyzing the mechanical state of rock mass engineering and for shoring and reinforce of rock mass. It is well-known that the wall rock state of laneway in fleet underground can be divided into three regions: zone of fracture, section of fictile limit balance, section of elasticity and initial rock stress. That can be analyzed by the existing theory of elasticity and plasticity. Rock mass stress measurements are classified to initial stress measurement and distributing stress measurement in underground engineering. Rock mass stress can be measured in boring holes, the open air and in the wall of underground excavation, and can be also obtained from reverse counting according to the displacement in two points in underground excavation. Rock stress measurement includes two methods: firsthand method and backhanded method. The below four methods are abroad applied firsthand methods: the flat jack method, the hydraulic fracturing method, rigidity rounding stress-meter method and sound-transmittal method. And the backhanded methods mostly include the outer-hole stress-release method, part stress-release method, relaxation strain method and geophysical soundex, and the outer-hole stress-release method is a more mature method in the backhanded methods. The hydraulic fracturing method, stress-release method and stress-comeback method are more applied usually.Initial stress measurement in the hydraulic fracturing method on the foundation of elasticity mechanics, the hydraulic fracturing mechanics former is predigested a plane strain problem. According to calculating and analyzing in theory, this plane strain problem can result in the potential rule and the essential character. First, analyzing the curve of rock stress measurement, we can obtain character press parameter P_b. P_r and P_s. And according to the corresponding academic calculation expressions, we can obtain the rock mechanics parameter values at measurement spot: most horizontal stress S_H , the least horizontal stress S_h and the tensile strength of rock in the hydraulic fracturing T_hf. And the split azimuth can be determined by making use of directional moulage method, in order to determining the azimuth of most horizontal stress. Second, according to the distribution features of the rock stress, combined with the mechanical parameters of the tunnel wall rocks, the stress filed in the tunnel area is simulated by using the three dimensional finite elements. Finally, according to the in-situ stress measurements and three dimensional finite element calculation, the basic features and distribution of the rock stress in engineering area are given, and the possibility of occurrence of geological hazards such as rock bursts during excavation of the tunnel is analyzed. Furthermore, the scientific basis for the lining design of the tunnel, choice of the tunnel's cross section and determination of the axial direction of the tunnel is provided.