| Southwest Hubei is the area where the karst is most developed and typical in ourcountry, the newly built Yichang-Wanzhou railway just lie in east Chongqing, andwest Hubei area, the topographical condition is specially scurviness. Along the railline the mountain is high and craggedness, rivervalley is evry deep. The karst landformis evry developed, the structure is complex and badnessly geology universaldevelopes. Shore deposit and shallow sea deposit carbonate rocks distributsuniversally, approximately composing 70% of the whole length of the railway. Thelength of bridge and tunnel approximately composes 72.66% of the total length, so itis one of most difficult lines in railroad construction history of our country. Speciallymany tunnels bury deeper than 500m, the greatest burying depth reaches 800m.Some tunnels pass under the subterranean river, underground water level is evry high, thehydraulic pressure is big, the greatest watere head difference reaches 300-400m.This paper depends on the karst hydrology geological investigation project of newlybuilt Yichang-Wanzhou railway, study the karst development regularity, thedistribution rule and its influence upon the tunnel construction. The objective is clear,so it has important theoretical and thepractical significance.This paper take the sixâ… level risk tunnels of Yichang-Wanzhou railway forexample, divide the whole line into four sectors, eastern part, middle part, mid-westpart and west part, and mainly take middle, mid-west, west part as research key, toanalyze the karst landform type, the karst developmental characteristic, summarize thekarst developmental regularity of each sector. On this foundation, particular analyzesthe tunneling influence of karst development upon the tunneling construction.1. In middle sector the basic landform type is plain hill and deep ravine, and thekarst watermigration pattern is gather water in syncline vally, longitudinal runoff,concentrative discharge. Karst development is controlled by stratum-lithology,geologic structure, landform and so on. The karst developmental feature mainly is:The karst development is intense. Karst development is inhomogeneous. karst waterssystem military suppliesarea Karst development is relatively homogeneous in recharge area, but in the runoff and discharge area, the karst development is extremelyinhomogeneous, concentrative karst cave and karst conduit as the main form. Verticalzoning of karst development is obvious, basipetal division as follow: The epikarst zone, erticalvadose zone, horizontal runoff zone, deep circulation zone, their developmental thicknessrespectively is 5～30m, 30～200m, 100～200m, 200～500m. The karst developmental regularitymay summarize as: the karst development has stratification, inhomogeneity and developing todeep.2.In mid-west sector the basic landform type are karst hilly depression, the dissolved-corroded fengcong vally. The karstwater migration pattern is dispersive and concentrativerecharge, vertical runoff to horizontal runoff transforming frequently, multilevel and concentrativedischarge. Surface and underground karst shape is developed which is mainly controlled bystratum-lithology, geologic structure, hydrodynamic force condition, basipetal division as follow:the ertical vadose zone, seasonal flucturation zone, horizontal runoff zone, deep circulationzone, and the karst development depth change obvious in different hydrogeology sector. The karstdevelopmental regularitycan be summarized as follow: Karst development is controlled bystratum-lithology, structure, lithological contact zone of dissolved rock and undissolved rock, andthe karst water system has the characteristic as multilevel discharge, but evry discharge level is notcomplete discharge. Through comparing the result, with hydrogeochemistry and isotopichydrogeology theory, it conducted the result that the source of bursting water in Maluqing tunnelis older sealed cavern water.3.In west sector the basic karst landform type is Karst ridge valley. By thecontrolling of anticline and fault, obstructing of undissolved rock, it forms thekarstwater migration pattern that is lateral recharge, anticline ridge runoff,concentrative discharge in karst conduit of longitudinal valley. Each kind of karst formis complete. Karst development is mainly controlled by stratum-lithology, geologicstructure, the hydrodynamic force condition. The karst developmental regularity maybe summarized as: karst develop along the rock lay, karst develops along structurefissure, karst develops along the fault, karst develops along different lothologicalcontact zone and karst is not developed in karst breccia.The influence of karst development upon the tunnel respectively is: 1. The inlet part of Baziling tunnel in middle sector lie in non-carbonate rock andthe impure carbonate rock area, so it does not encounter the harm of karst water. TheDalupo storage structure of syncline is the most possible location where it mayencounter static reserves with high hydraulic pressure. Chuanxinping storage structureof syncline is lie in the outlet part, and it may encounter mid-scale bursting water andkarst cave in the contact strip between P2c and P2w. The karst point of Yesanguan andDzhiping tunnel area mainly lies in syncline core and anticline wings, so it mayencounter large scale bursting water and mud when the tunnels pass through thesespots. because the majority of Yesanguan tunnel and Dzhiping tunnel are located indeep circulation zone except the inlet and outlet of Dzhiping tunnel, it is advantageousto the tunnel construction.2.In Maluqing tunnel area of the mid-west sector, the subterranean river is nettyand ramose, and the majority of tunnel is located in the ertical vadose zone, seasonalflucturation zone, horizontal runoff zone. The most dangerous section are Niaolahevally and Xiaomatan-Liangfengdong subterranean river. There is a big low resistivityanomaly zone nearby the tunnel route correspondence those two positions. The karstcave where the 1.21 accident happened was disposaled, so its influence to the tunnel issmall. The karst is evry developed in Baiguoba anticline wings and the contact zonebetween Cambrian carbonate and Ordovician aquifuge in Yunwushan tunnel area, andmany cave were disclosed, so it may encounter large scale bursting water in rainyseason.3.In west sector, carbonate rock in Qiyueshan tunnel area approximately compose47% of the tunnel total length. The main possibly bursting water sector of tunnel areaare:Deshengchang valley area, Qiyueshan anticline core and its two wings. Theconcrete spot are: nearby the fault zone, along structure fissure, the completecalcareous rock contact strip and lithological contact zone of dissolved rock andundissolved rock(or karst breccia). |
