Study On The Performance Of RPC Of Ultra-high-strength Drilling Shaft Lining And Mechanical Properties Of The Shaft Lining Structure In Western China

The development of deep coal resources increases the depths of a newly-built shaft that passes through water-rich and weakly cemented strata;moreover,the external load on the shaft lining structure increases when the drilling method is adopted Therefore,an ultra-high-strength shaft lining structure must be adopted to resist the impact of strong external loads.The concrete composite shaft lining structures currently used in China in the middle and lower support of deep shaft drilling are mostly the inner-layer steel platehigh-strength reinforced and the double-layer steel plate-high-strength concrete structures.Although these two structure types have a high strength,the construction is costly while the processing technology is complicated.Notably in a case of a high degree of groundwater mineralization in the western region,the inner steel plate of the shaft lining corroded severely after a long time.The corrosion considerably reduced the bearing capacity of the shaft lining structure.Therefore,this paper proposed the use of reactive powder concrete(RPC)with ultra-high-strength and high durability as a new drilling shaft construction material,and selected the method of combining laboratory tests,theoretical analysis,similar model tests,and numerical simulation to carry out a systematic study on the performance of RPC of ultra-high-strength drilling shaft lining and mechanical properties of the shaft lining structure in western China.The results of this study have important engineering application value for solving the problem of shaft support in deep and large diameter drilling in western China and realizing the rapid construction of “one drilling and forming process”.The main research contents and achievements of this paper are as follows:(1)The orthogonal test method was used to test and optimize the RPC of drilling shaft lining,and the range analysis method was used to systematically analyze the primary and secondary order and significance level of the effects of silica fume,quartz sand,quartz powder,and water-binder ratio on the compressive strength and splitting tensile strength of the RPC of ultra-high-strength drilling shaft lining.Combined with the comprehensive balance method,the optimal mix ratio of RPC was finally determined.Then,RPC110 and RPC140 were prepared by standard curing and autoclave curing,respectively,and their basic mechanical properties were obtained.Additionally,combined with hydration products and micro-morphology characteristics,the mechanism of autoclave curing to improve the macroscopic mechanical properties of RPC was revealed.(2)The permeability test of RPC during the whole stress-strain process was carried out under the coupling of stress and seepage.Based on the test results,the characteristics of RPC strength and deformation failure corresponding to different stress loading stages were analyzed,and the permeability evolution of RPC in each loading stage was clarified.Simultaneously,X-ray computed tomography(X-CT)technology and AVIZO software were used to establish a 3D meso-equivalent pore network model of RPC,and the MIP test was used to compare and verify the relationship between its permeability properties and pore characteristics.The research shows that compared with C70 high strength and high performance concrete,RPC generally exhibited low permeability characteristics while its permeability evolution law corresponded to the stress–strain relationship under triaxial loading.For RPC140 with autoclave curing,the internal pore size is significantly reduced,and the pores are more sparse,limiting a direct connection between the pores.Thus,the specimen is unable to form a dominant seepage channel.(3)By using the accelerated corrosion test method and taking C70 high-strength and high-performance concrete as control,the experimental study on the durability of RPC of drilling shaft lining eroded by different concentrations of composite salt solution was carried out.The mass loss rate and the corrosion resistance coefficient of compressive strength were used as the basic evaluation indices of concrete durability,and the macroscopic mechanical properties and apparent morphology deterioration of C70 highstrength and high-performance concrete with RPC were compared.By introducing the Drucker-Prager criterion and using the Weibull statistical method and damage mechanics theory,a triaxial compression damage constitutive model of concrete under composite salt erosion was established.Then,combined with experiments,the distribution parameters of the constitutive model and its rationality were solved and verified,and the variation characteristics of the total damage variable and damage development rate were analyzed.(4)By using the accelerated corrosion test method and taking C70 high-strength and high-performance concrete as control,the experimental study on the durability of RPC of drilling shaft lining eroded by different concentrations of composite salt solution was carried out.The mass loss rate and the corrosion resistance coefficient of compressive strength were used as the basic evaluation indices of concrete durability,and the macroscopic mechanical properties and apparent morphology deterioration of C70 highstrength and high-performance concrete with RPC were compared.By introducing the Drucker-Prager criterion and using the Weibull statistical method and damage mechanics theory,a triaxial compression damage constitutive model of concrete under composite salt erosion was established.Then,combined with experiments,the distribution parameters of the constitutive model and its rationality were solved and verified,and the variation characteristics of the total damage variable and damage development rate were analyzed.(5)Based on the dimensional analysis method,the similarity criterion of ultra-highstrength RPC-steel composite shaft lining was derived,and the triaxial loading and testing system of shaft lining was set up.Using RPC as the wall construction material,the similarity model test of ultra-high-strength drilling shaft lining structure under standard curing and autoclave curing system was carried out.The mechanical characteristics and strength characteristics of ultra-high-strength RPC-steel composite drilling shaft lining were studied.The strength criterion of ultra-high-strength RPC of drilling shaft lining and the calculation formula of compressive strength improvement coefficient was established.Additionally,the ultimate bearing capacity calculation formula of this kind of shaft lining was constructed based on dimensional analysis and regression analysis.Taking the north air shaft of Taohutu Coal Mine as an example,considering the strengthening effect of RPC in a multi-axis state,the safety of the drilling shaft lining structure was determined and its wall thickness was optimized,which proves the feasibility of reducing the initial design wall thickness of autoclaved RPC140 drilling shaft lining from 1062 mm to 900 mm.(6)A numerical calculation model of ultra-high-strength RPC-steel composite shaft lining structure was established,and the stress distribution characteristics of RPC of drilling shaft lining under uniform horizontal load were obtained,and the results were compared with the model test results.By using the method of controlling a single variable to change the influence parameters,its influence on the ultimate bearing capacity of shaft lining was analyzed.Additionally,based on the numerical results of ABAQUS software,the five factors of thickness-to-diameter ratio,RPC strength grade,reinforcement ratio,steel strength grade,and steel fiber content were comprehensively considered,and the ultimate bearing capacity calculation formula of ultra-high-strength RPC-steel composite shaft lining structure was further improved.Figure [92] Table [39] Reference [188]...