Research On The Permanent Support With Shotcreting And Bolting Structure And Its Design Method In Oil And Gas Pipeline Tunnel

With the development of the Belt and the Road,the international cooperation for oil and gas pipeline on a large scale has been expanded.The planning and building multiple energy corridor are being continuously increased and there will be more than 150000 kilometers oil and gas pipeline at the end of 2020.The construction of oil and gas pipeline will become the main point for government-led investment,crossing pipeline tunnel has become the normalized control engineering in the mountain areas,the construction quality of tunnel engineering is directly related to the quality and operation safety of oil and gas pipeline.The composite lining by NATM is used in the pipeline tunnel at the present stage,with a small section size and large longitudinal gradient,however,the composite lining by NATM is constructed at low speed,but having high construction cost and even poor security.From the strategic demand of China's oil and gas pipeline tunnel construction,there are lots of new craft and technique challenges that have never been encountered before to meet the high quality and high security requirements.Therefore,the research on the permanent support structure of shotcrete and anchor,especially the permanent support structure and its design method of the oil and gas pipeline tunnel,also providing the technical support for the revision and improvement of the existing provisions for General regulations on design for mountain tunnel of the oil&gas pipeline project has great practical significance and engineering demonstration effect.Based on the project in the Petrochina Company Limited scientific research and technological development item "Research on safety of lining support structure with shotcrete and anchor and structure of oil and gas pipeline tunnel "(Grant No.XVQ-V-52(50)-2013),by using theoretical analysis,laboratory test,numerical calculation and in situ test are adopted,the permanent support structure and its design method for the oil and gas pipeline tunnel are studied systemically in thia paper.The main results and conclusions are as follows:(1)Based on a large number of engineering practice and the existing domestic and foreign shotcrete and anchor structure specification,comprenhensively using engineering analogy,field test and so on,the design parameters of the permanent support structure of the shotcrete and anchor in the pre design stage of the oil and gas pipeline tunnel are determined,at the same time,the rationality of the design parameters of anchor bolt is verified by the field loose circle test.(2)The high-performance Spray Concrete mixture rate design method has been proposed.The result of basic mechanical performance test and the durability test shows that the design strength of the 6 kinds of mixture rate all meets the technical standard of C35,and the mixture rate with fiber is excellent in toughness and durability.(3)According to the laboratory test,the effect mechanism of the early mechanics of high performance shotcrete has been revealed and the mechanical properties of high performance sprayed concrete at different age have been proved,in view of the early mechanical properties the recommended mixture rate is given;The calculation method of the hardening process mechanical properties of the high performance sprayed concrete(bond strength,equivalent elastic modulus and compressive strength)has been put forward considering the distribution coefficient and the characteristics of steel fiber through the comprehensive means of theoretical analysis,literature research.(4)Using discrete element method,stimulate the steel fiber prayed concrete generation process,establish the three-dimensional discrete element mechanical non-linear model of steel fiber prayed concrete adopting the actual prayed concrete mixture rate.In view of the stress-strain curve of steel fiber reinforced concrete,the mechanical model is calibrated.The development law of the steel fiber sprayed concrete crack in the basic mechanics numerical test(UCS,Three point bending)has been proved.The failure characteristics and toughening mechanism of the steel fiber sprayed concrete has been revealed from the micro level.(5)From statistical results of different span(3.3m?32m),the rock level(? to ?),depth(5m?100m)large number of section(173)field tests,the radial contact pressure value and the distribution form of the shotcrete permanent support structure have been obtained,which can provide technical support for structure desagn and construction of oil and gas pipeline tunnel.(6)Considering the high-performance spray concrete "coupling effect of mechanical properties evolution at early age and surrounding rock",a three-dimensional model of construction mechanics has been built to reveal the temporal and spatial distribution of stress and deformation characterastics of shotcrete support structure in the gas pipeline tunnel at early age;based on the superposition theory,considering the hardening characteristics of shotcrete,a new method to evaluate the combined structure of the permanent support structure has been put forward to establish the safety evaluation method of the permanent support structure.(7)Based on the damage theory,and combined with the results of laboratory experiments,a method to determine the damage parameter of steel fiber prayed concrete has been put forward on the basis of the stress-strain curve of steel fiber reinforced concrete.The damage evolution process of the shotcrete permanent support structure has been proved by the layer-structure model.The safety evaluation method of the shotcrete permanent support structure based on the damage mechanics has been created.(8)The methods of theoretical analysis,laboratory test and numerical analysis were used and tensile softening properties of high-powered sprayed steel fiber concrete at early age were analyzed to acquire the relationship about bending-curvature.The limited crack width and curvature of high-powered sprayed steel fiber concrete were confirmed and the evaluation methods of entire life cycle durability for high-powered sprayed steel fiber concrete were formed.(9)By Limit State Design Method,analyze the damage characteristic of lining structure and the safety of the composite structure of the whole construction process,evaluate the safety of entire life cycle for Shotcrete Support Structure under the indexes of both Limit State Design Method and Composite structure method.Finally,the design method considering safety and durability of structure was established.