Study On Mechanical Behaviors And Control Measures Of The Pipe-Jacking Method Applied For Excavate Hign Level Suction Roadway In Deep Coal Mine

Coal industry has entered the deep mining area below 1000m in China.At present,the deep roadway accounts for 28%`30%of the total 6000km roadway drtving in china.It becomes increasingly difficult to excavate the roadway because of the complex geological environment of deep high ground stress,high ground temperature and high permeability.Traditional drilling and blasting method and fully mechanized digging machine were difficult to meet the requirements of safety,economy and rapid modernization about deep coal mine roadways anymore.Intensification and mechanization are becoming the trend and goal of deep coal mine roadway's construction.Equipment of pipe jacking is portable,which is suitable for deep roadway of coal mine.Since workers can control pipe jacking machine in cavern and the rest work of tunnelling,tapping and supporting will be done automatically,workers needn't to work in tunnel face in pipe jacking construction,which can avoid injury accident from runnel face collapsing and gas outburst.For existing methods having dilemmas of low construction speed,abominable construction environment and poor economic benifits in small section hard rock roadway,once pipe jacking method is applied in roadway construction in deep,rocky environment,it will acheve coal mine safety production,dustless construction and labor intensity reduction to the most extent,which will be breakthrough for intelligent unmanned mining technology in deep,rocky environment.Since structure characterisitics,mechanical behavior and construction respones of rock mass in deep environment is essentially different from rock mass in shallow,roadways in deep,rocky environment and tunnels in shallow environment face completely different construction environment,which mean existing theory and technology of pipe jacking for shallow tunnel no longer suit.At present,correlative theory of pipe jacking in deep,rocky environment is still blank,thus this paper study on a series of rock science and roadway construction problems arround the application of pipe jacking in deep,rocky environment.All the achievements in this paper belong to research project of"Intelligent pipe jacking and rapid drilling technology and equipment",the subproject of"Coordinated development of coal and coalbed methane",which is one of the major project of the thirteenth national technology oil and gas research project.In this paper,elastic plastic theory is uesed to analyze the deformation of surrounding rock and the top force of circular tunnel constructed by pipe jacking method.Basing Heim hypothesis and low plastic strain level of small section circular roadway in deep environment,this paper firstly proposes mathematical description of rock creeping of surrounding rock of small section roadway basing Burgers model,and deduces calculating formula of overbreak amount?35?R.From the example analysis provided in this paper,the elastic radial deformation of small section roadway?r=1.5m².0m?is small?less then 10mm?,even though roadway in soft rock stratum?E=4.5GPa?and in high ground stress level?_vp=30MPa?.Normally,overbreak amount of pipe jacking construction is about 50mm,thus pipe will not be stucked by the surrounding rock under transient radial deformation of roadway.According to derivation process in this paper,the long-term radial deformation of roadway is instable and radial deformation of roadway develops rapidly in initial stage?increasing 45.5%of transient deformation in 24h,57.6%in 48h and 62.0%in 96h?,then turns into stable growth in long-term stage.For example analysis provided in this paper,growth rate of long-term radial deformation development is about 0.0084mm/d,which mean long distance pipe jacking construction must keep jacking speed exceed a minimum value,otherwise,pipe will be stucked by surrounding rock in long-term pipe jacking construction.Theoretical analysis also point out that radial deformation of surrounding rock can be reduced and stabilized by appropriate grouting.In this paper,the discrete element PFC3D program is used to systematically study the creep characteristics of the roadway.Firstly,we use burgers contact model in PFC3D program to calibrate the microcosmic parameters of silt rock which roadway locate in.Data from virtual creep test will be compared to the data from laboratory creep test,and verify the applicability of discrete element method analyzing rock creeping problem,and then,we build plane strain discrete element for roadway and get data of stress and strain in different radial direction by setting measuring balls.With the example of NO.1413A high drainage roadway in the north part of ZhangJi mine,numerical simulating solution of discrete element method agree well to theoretical solution,which make theoretical method a meaningful reference for further research.Basing correcting method for pipe jacking construction,this paper firstly proposes quadratic function can be used to describe the travelling curve of pipe jacking in deep,rocky environment,and receives mathematical description of the relationship between travelling curve and pipe jacking resistance,which can be simlified into correction factor K and shown in the paper.Since pipe jacking construction closely relates to surrounding rock,this paper derives different rock massinto typeI,II,III and IVaccording to pipe jacking resistance.From the analyzing example in the paper,maximum deviation of travelling curve will increase with smaller correction angle,which also lead to further correction curve and less stability of pipe jacking.The most sensitive factor of maximum deviation is initial deflection angle₀?,and with bigger initial deflection angle,maximum deviation increases?with₀??28?1°,travelling curve deflect 3.5cm per each pipe without correction?.Correction angle?also a key factor of maximum deviation,and with bigger?,maximum deviation reduce.Thus when pipe jacking deflection occur,we should measure deflection angle firstly and correct travelling curve if deflection angle is overlimit even though inifial deviation is small.Even in deep,rocky environment,deflection angle should not exceed 1^o.With correction angle remain unchanged,pipe jacking force loss more serious as jacking distance getting further.With jacking speed higher,pipe jacking resistance get bigger and construction period get shorter which mean not easy to get stuck since radial deformation develop little in short term.Therefore,pipe jacking construction in deep,rocky environment should balance the relationship among pipe jacking force,correction angle and overbreak amount.This paper use finite element method to analyze stress state of pipe with elastoplastic model,and verify applicability of this method by full scale test.This paper also firstly proposes classification method of surrounding rock which exclusively suitable to pipe jacking construction in deep,rocky environment.Basing uniaxial compressive strength of rock,integrity of rock mass,ratio between uniaxial compressive strength of rock and ground stress value and slag material condition,this paper classifies deep surrounding rock mass into four types,from good for construction to bad,shown astypeI,II,III and IV.Type I rock mass can form stable surrounding rock which is very suitable for pipe jacking construction,and can reach higher jacking speed and not easy to be stucked.Type II rock mass is less stable,but still suitable for pipe jacking construction.For type III rock mass,pipe jacking method still can be used in roadway construction,but it is easy to be stucked and necessary measures such as setting more relay rings,setting higher grouting pressure and setting bigger overbreak amount should be executed.Type IV rock mass is no longer suitable for pipe jacking construction,traditional method such as blasting method and comprehensive tunneling method will be more suitable.With field test data of first pipe jacking experiment in deep,rocky environment,we found that deformation of surrounding rock is small in small section circular roadway,which coincides well to theoretical research and verifies theory of surrounding rock deforming.By absorpting experience from pipe jacking construction in deep,rocky environment,this paper also proposes improving proposal for equipment,material of pipe and construction technique,which can be ready for the next large field test.In this paper,the applicability of pipe jacking construction in deep,rocky environment is discussed,and the theoretical and technical system of pipe jacking construction in deep coal mine is preliminarily constructed,which can analyze the feasibility of different formation and guide pipe jacking construction in deep,rocky environment.Research result of this paper has important theoretical significance and application in pushing roadway construction technique in deep,rocky environment.With the application of pipe jacking method in deep,rocky environment,more field data and experience need to be accumulated for further studey.