Research On Fracture Mechanism Of Shaft-lining And Control Technologies For Deep Vertical Shaft In Unstable Soft Rock

After the deep part is under exploration of resource, deep vertical shaft develops rapidly and large amounts of vertical shafts which are about some kilometers in depth have sprung up in the country. And when the deep is reached, vertical excavation meets such technology problems about supporting as poor self stability of surrounding rock, big deformation, expanding and softening with water. Relevant theory about vertical shaft in surface ground cannot be applied to deep vertical shaft development any longer. Because the extension direction of soft rock tunnel is different from that of vertical shaft,experiences of support technology and theory basis which are used for deep vertical shaft construction are not thoroughly reasonable. As a result, take Niaoshan Mine as research object, investigate and analyze structural fracture features of deep shaft lining and summarize the factors leading to the fractures.By means of field monitoring, laboratory experiment and test, theoretical analysis and numerical calculation, study such factors as nonuniform confining rock, surrounding rock with water, seasonal temperature change and their influence on stress distribution of shaft lining, as well as how self structure strength influences bearing capacity of shaft lining.And stress condition of shaft lining under uniform load can be taken as criterion. Determine the weight of what influence outer factors have on structure stress. Under the direction of this, to begin with, reinforce surrounding rock and homogenize the stress of shaft lining, then come up with measures to avoid the structure damage of shaft lining of soft rock in deep vertical shaft.(1) According to the tracking investigation aimed at working condition of structure of shaft lining and surrounding rock behind shaft lining in different depths of vice shaft in Niaoshan, conclusions are in the following:with the increase of depth of the rock, self stability and uniformity are worse and worse; Based on the damage degree and surface features, fracture phenomena of shaft lining can be classified into ranges of different depth. Damage phenomena of the structure of shaft lining for vice shaft in Niaoshan Mine can be classified into three critical depths,that is,500m～700m、700m～850m、850m～1000m.(2) Testing result of water content of surrounding rock behind shaft lining indicates:after surrounding rock is permeated by water, change of the amount of humidity is a power function of position radius. After substituting that into displacement function caused by the change of humidity, the pressure which the effect of the rock expansion under water give to shaft lining can be figured out according to deformation compatibility condition. The pressure can be influenced by humidity, linear expansion rate, elasticity modulus and permeation.(3) According to monitoring result of spot temperature, temperature stress in shaft lining caused by seasonal temperature change and water inrush are calculated respectively. Analysis show that the stress caused by both is so small that it brings no damage to the shaft lining. Use the computing method of time-division and space-division, and take full account to the change of elasticity, then stress induced by hydration heat in the region of over-excavation. The result shows that tangential compressive stress around the edge finally caused by hydration heat is maximally 1.15MPa. While the inner tangential tensile stress is maximally 0.35MPa.(4) Test on physical and mechanical property of the rock, and monitoring of the load of shaft lining show:the mechanical property is so various in the surrounding rock, and side pressure of shaft lining is uneven, and it has no laws. Given that nonuniform confining pressure is distributed in the form of relatively conservative double angle formula formula, that is, according to calculation and analysis, under the condition of uniform side pressure, there are extreme points in tangential stress inside shaft lining. If the thickness-diameter ratio is too small or the coefficient of nonuniform confining pressure is too big, tensile stress occurs at the minimum point which has a bad influence on the safety of structure.(5)Tests of concrete strength and physical parameters under the action of loads show that: Low loading rate is in favour of concrete curing,and can effectively improve the strength; and concrete damage usually happened due to high loading rate. Test results of groundwater quality and wall strength show that, poor quality shaft-lining is easily erosioned by groundwater, and its strength loss 10 percernt after 36 months.(6) Take the condition under uniform load as standard, then compare and research the influence which nonuniform confining pressure, rock with water affecting, and temperature change have on the stress of shaft lining. Research shows that nonuniform confining pressure has the worst influence on the stress state of shaft lining, while the deformation induced by water has second worst influence, and temperature change has the least influence. As a result, when doing the research of fracture prevention technology, start with water-blocking and reinforcing surrounding rock, and uniforming stress.(7) With comprehensive geophysical prospecting, after verifying headwaters and water inrush tunnel, start with water-blocking and reinforcing rock, and come up with technology of segment coupling umbrella grouting, also weaken the influence which tangential hydrops has on surrounding rock. Use the grouting method that input is combined with output and added in several times.Replace the soft rock in structure which is disrupted and softened. Make up for the deficiency caused by shrinkage of serous fluid. Promote the effect of handling the deformation which watering lead to in rock.(8) Start with homogenizing the force inside the shaft lining, and come up with solutions that improves the structure. Research show that conventional method to add the thickness of shaft lining is not applied just when the coefficient of nonuniform confining pressure is small. For structures which is circular inside and elliptical outside, solution of positive loading does better in homogenizing force than that of passive loading. By accommodating the pressure of air cushion behind the shaft lining, new compress could control the structure, homogenize the load totally, make full use of carrying capability of the structure, releasing the pressure of rock, and make room for the suitable deformation.