| With the vigorous development of economy and the continuous improvement of infrastructure,tunnel and underground engineering in China have been rapidly developed.The geological environment faced during tunnel construction is also increasingly complex.Strong karst,large-depth,high ground pressure,and extremely complex geological structures often lead to water and mud inrush disasters,which have become one of the main geological factors that restricts the safe and rapid construction of tunnels.Unclear understanding of the hazard-inducing environment and inaccurate identification of water and mud inrush are the main reasons why water and mud inrush disasters occur frequently and are difficult to prevent.“water and mud inrush hazard-causing system and disaster assessment of intermittent type of water and mud inrush of filled karst cave in tunnel”was the main research object in this paper.Relying on engineering examples such as Qiyueshan tunnel of Lichuan-Wanzhou expressway,through literature and site investigation,software development,theoretical analysis,experimental device development,laboratory tests,typical case analysis and other means,research were carried out from the following three aspects,i.e.,hazard-causing systems for water and mud inrush in tunnel,resistance body assessment method and software of water and mud inrush in karst tunnel,and critical hazard criterion of intermittent type of water and mud inrush of a filled karst cave in tunnel.The following research results were obtained.(1)More than 300 cases of water and mud inrush in tunnels were investigated and analyzed.The distribution characteristics of water and mud inrush tunnels were obtained.The hazard-causing system of water and mud inrush was classified into 3 categories including 1 1 types.The first category was karst,which was about 45%,including 142 cases.The karst category included 3 types,i.e.,the corrosion fissure type,the karst cave type,the piping and underground river type.The second category was fault,which was about 28%,including 86 cases.The fault category included the water-enriched fault,the water-conductive fault and the water-resistive fault.The third category was due to the other causes,which was about 27%,including 84 cases.Other causes category included the intrusive-contact type,the structure-fissure type,the unconformable-contact type,the differential-weathering type and the special-condition type.The structural characteristics,occurrence regularity and identification methods for different types of water and mud inrush hazard-causing system were proposed.Typical cases of each type of water and mud inrush hazard-causing system were analyzed.The hazard-inducing process of water and mud inrush in tunnel was studied and four typical hazard modes of water and mud inrush in tunnels were proposed,i.e.,the directly revealed type of water and mud inrush,the progressive failure type of water and mud inrush,the seepage instability type of water and mud inrush and the intermittent failure of water and mud inrush.The process of hazard-inducing and development of water and mud inrush and its characteristics were described.(2)A Resistance Body Assessment Method(RBAM)against water and mud inrush in karst tunnel was proposed,which can used for rapidly evaluation in tunnel site.An evaluation index system was put forward for this method,which took the thickness of resistence body,unfavorable geology,hydrodynamic condition,characteristics of surrounding rock into consideration.In addition.classification methods and criterions for the evaluation index system were put forward.Grades and score tables were created for efficient evaluation based on aforementioned methods and criterion of classification.The implementation process of the method was expounded.A resistance body assessment software of water and mud inrush in karst tunnel was developed,which realized the routinization and interface of the RBAM and simplified the evaluation operation,and was easy to be popularized and used.The assessment result of a railway engineering was consistent with the actual condition,which proved that the proposed method was rational and feasible.(3)Different failure types of first water and mud inrush and hazard-causing factors of secondary water and mud inrush were studied,and corresponding critical hazard criterions were established.The determining method of the most dangerous sliding surface was proposed for the integral sliding failure of the weak permeability filling medium,and the calculation formula of the force on resistance body was derived.The proposed mehod was verified by Rankine active earth pressure theory.Based on the elastic beam theory,the calculation formula of minimum safety thickness of intact and fissure-containing resistance body were established respectively on the basis of tensile strength and shear strength criterions.And the influencing factors of the most dangerous sliding surface and the minimum safety thickness were studied.To solve the problem of seepage instability in strongly permeable filling medium,a variable-section spiral capillary model for piping in non-cohesive soil was established.Considering the actual flow bending problem of the seepage channel,the concept of capillary pipe curvature was introduced.The relationship between the curvature and soil grain composition,porosity and permeability coefficient of skeleton soil were established.By introducing the concept of helix angle,the relation between the curvature and the inclination of the seepage channel was established.According to the different of fine particle content in the pore of particle framework,considering and ignoring the interaction between the particles,the critical hydraulic gradient formula of fine particles incipient motion were established respectively.For secondary water and mud inrush,the critical hazard criterion considering desilting and rainfall was established,and the hazard-causing mechanism of intermittent type of water and mud inrush in tunnel was revealed.(4)The sedimentary characteristics of filling medium in karst cave influence the characteristics of water and mud inrush in tunnel.An integration test equipment for karst cave sedimentary and tunnel intermittent type of water and mud inrush was developed.The device included four parts,i.e.,stirring device,horizontal flume,vertical deposition device and water and mud inrush control device.The main body was made of high transparency plexiglass.The material of the device realized the visualization of the filling medium deposition process and the intermittent type of water and mud inrush process.Deposition tests of karst caves were carried out.The characteristics of layered deposition of karst caves and the influence law of distance and particle size were revealed.The intermittent type tests of water and mud inrush were carried out.The catastrophic processes of secondary(multiple)water and mud inrush caused by desilting and rainfall were reappeared.The influence of head height,sediment height and grain composition on tunnel intermittent type of water and mud inrush were studied.The results showed that as the height of the water head increased,the development time of the first water and mud inrush in the tunnel was shorter,faster and the sediment inrush increased.As the sediment deposition height increased,the longer time the tunnel water inrush occured.The larger grains of filling medium,the later water and mud inrush in the tunnel occured,and it was prone to be intermittent type of water and mud inrush.(5)An intermittent type of water and mud inrush in Chaoyang tunnel of Guizhou-Nanning high-speed railway was studied.The disaster process and the chracteristics of filling medium were analyzed.The failure mode of first water and mud inrush was considered as seepage instability type of water and mud inrush through grain composition analysis.By analyzing psephicity and mineral characteristics of karst cave filling medium,and considering the characteristics of water and mud inrush and hydrogeology in tunnel site,the water source was founded.The reason was that the karst cave had a hydraulic connection with the underground river.The cause of karst caves development and water and mud inrush were reveald by analyzing the lithology,topography,rock dip,rainfall and ground water sources,which provided useful re ferences for tunnel construction.The result of the resistence body assessment showed that the water and mud inrush was a lag-type failure,which was consistent with the actual project. |
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