| With the shift of the coal industry’s center of gravity to the west,the construction of new coal mines in Inner Mongolia,Shaanxi,Ningxia and other places still needs to be carried out.However,most of the shafts of these new coal mines need to pass through deep chalk and Jurassic rock formations,which are weakly consolidated,low strength,sanded and mudred in water,so special Wells need to be dug.Drilling method has the advantages of good working environment,high degree of mechanization,construction safety and so on.It is the development direction of deep shaft drilling in the future.However,in northwest China,the winter climate is dry and cold with strong wind,so how to ensure the quality of drilling wall construction in such a cold winter has become a technical problem to be solved urgently.Therefore,this paper takes the central return shaft of Kekegai Coal Mine,which is the first to be constructed by drilling method in western China,as the engineering background to carry out the research on the preparation of precast construction concrete and the crack control of drilling shaft wall in winter in cold regions.First of all,based on the principles of thermodynamics and material mechanics,the thermal calculation of precast concrete materials and the calculation of hydration temperature rise after pouring are carried out in the cold region in winter.Therefore,it is suggested that steam curing shed is necessary for concrete construction of drilling well wall in cold region in winter to ensure that no freezing damage occurs during concrete curing.Secondly,through the selection of raw materials and a lot of preparation tests,the mix ratio of drilling wall pumping high-performance concrete is obtained.The early mechanical properties of commonly used strength grade concrete for drilling well wall were studied through laboratory tests,and the evolution law of various mechanical properties was analyzed.On this basis,the concrete mix ratio is further optimized to reduce the hydration temperature rise of concrete.Then,in the central return shaft construction site of Kekegai Coal mine,the temperature sensor was embedded in the prefabricated shaft wall to measure the temperature of concrete during the pouring and curing of the shaft wall,and the temperature variation rule of concrete inside the shaft wall was analyzed,which provided a basis for studying the stress and deformation of the shaft wall concrete and numerical simulation.The measured results showed that: When the pouring temperature is 10℃,the maximum core temperature of shaft wall can reach 35.3℃,the maximum temperature difference between inside and outside is 14.5℃,and the core temperature drop difference is 26℃.Then,taking the inner steel sheet concrete composite well wall of the central return shaft of Kekegai Coal mine as the research object,a calculation model was established by using the large numerical simulation software FLAC3 D to simulate and analyze the internal temperature field and stress field of the inner steel sheet concrete composite drilling well wall during precast construction and maintenance.The research results show that,The constraint of the inner steel plate is the main factor affecting the internal stress of the borehole.The maximum tensile stress of the inner steel plate is 3.95 MPa,and that of the inner steel plate is 0.71 MPa.The change of ambient temperature will also affect the stress inside the shaft wall.The peak tensile stress in the shaft wall will change with the ambient temperature when concrete is poured.The higher the ambient temperature is,the higher the peak internal temperature will be and the earlier the peak time will arrive.Concrete should be poured at a temperature of 5～10℃.At the same time,the orthogonal design method is used to establish the calculation model,and the three factors affecting the internal stress of concrete(environmental temperature,comprehensive heat transfer coefficient,concrete strength grade)are calculated and analyzed.The results show that the order of influence is: comprehensive heat transfer coefficient > environmental temperature > concrete strength grade,which provides the foundation for the later control of borehole wall temperature crack.Finally,according to the above research results and the analysis of the mechanism of shaft wall cracking,the technical measures for the early crack control of drilling shaft wall are proposed to provide technical support for the winter precast construction and crack control of drilling shaft wall in cold regions.Figure [31] Table [30] Reference [81]... |
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