Monitoring in Building Road Tunnel Across Coal Measures

地球与环境05年第33卷第3期162EARTH AND ENVIRONMENVol.33No.32005rticle ID:16729250200503-0162404Monitoring in Building Road TunnelAcross Coal measuresXIE Ye, ZHANG Dong-ming, KANG Hui-ming(I. Chengdu University of Technology Chengdu 610059, China 2. College of Resource and EnvironmentalScience, Chongqing University Chongqing 400044, China 3. China PertoleumEngineering CO., LTD. Southwest Company Chengdu 610030, ChinaAbstract In some cases coal measures goaf, big caves and huge faults as well as high initial stress cannot be avoided in road tunnelexcavation. These geological features may make it more difficul practical tunnel construction. So it is necessary to take strong precautious measures against gas outburst water bursting and roof fall in a tunnel across coal measures with risk of gas outburst. The techniques such as advance drilling exploration multiple-cycle shallow depth hole controlled blasting reinforced supporting which in-clude concrete grouting and twice supporting, and monitoring measures are often applied in the construction of tunnels and satisfied re-sults are achieved. Results in this paper can help others to get experiences in road tunnel construction with similar geological featuresKey words road tunnel coal measures gas outbyCLC number P642Document code :A1 IntroductionMethod NATM ) In thisbuilding and safetynitoring in building the tunnel across coal measures at theFollowing the development of highway constructionwestern entrance of the right line is introduced brieflyin Southwest China, road tunnel problems are put forward frequently. Mountains and hills spread all over Si2 Geological conditionshuan Province. Some expressways have to pass theseAccording to the geological explorationandareas.The Huayin Tunnel, which is located in the designing, the rocks and coal measures, whichHuayin Mountain area was a key project of Guang-Yunel goes across are Permian in age. The coal measuresvary in thickness between 1. 97-2. 61 meters,conEessway. It was designed to be a single way line tained by the first period of those measures,was theunnel, i.e., there were two tunnels involved in this main mining coal measures in this area. The westernThe distance between the two tunnels is 40 entrance mileage was YK33 +750 from the point wheremeters. The whole length is 9389. 95 metersleft the tunnel passed through coal measures( PTC).Thedepth of PTC is 438. 6 meters. Min coal measures haveone is 4795. 95 meters long and the right one is 4684an average thickness of 2. 55 meters, the elevation an-meters long. The Huayin Tunnel is one of the longest gle is 63 degree, gas pressure is 1. 87 MPa, and gastunnels in China. In this area the geological conditions content is 8. 94 cubic meters per ton. According to theare very complicated, including coal measures coalscheme of classification, gaseous coal measures belorto coal rock)and gas outburst coal measures. Tianchiwaste, huge fractured zone cave gas gasoline gascoalf +he huayin tunnel areahigh initial stress around the Huayin Tunnel. The tun中国煤化ich passed through thenel was constructed by the New Austrian TunnelingtuniCNMG540, 640 and 790 meReceived date 2005-06-08ters high. Among them, No 540 horizontal main driftFoundation item: Doctoral Funds of Ecucation Ministry of China( 2m61115)intersected with YK33 +771 mileage of the tunnel inBiography XIE Yd 1976-), female editor of Geological Hazardone cross section The第3期XIE Ye et al. Monitoring in Building Road Tunnel Across Coal Mea163lowest point of No 540 drift and its goa36 age. Then, the lower section was excavated. Becausemeters from arch point in the cross section of the road of gas outburst hazard and short distance between Ptotunnel. The goaf was closed 9 years ago. So plenty of and Tianchi mine goaf, blasting working of touchingas and water was accumulated, the surrounding rocks and excavating of the coal section must be short work-were severely unstable due to the development of frac- ing cycle( 1.5-2. 0 meters per working cycle ) multures. The conditions would affect road tunnel s stabil- tiple working cycle and long distance blasting. Thus,itcould be done well to prevent gas outburst and tunnel3 Excavation across coal measureselapsing. In blasting working the millitor and electric initiating device were adoptedAccording to local geological conditions meticu- 3. 3 Coal section supporting( structurelous schedule should be instituted in the coal section toWith the aim of preventing outburst collapse andprevent coal and gas outburst, and collapse of coal water and local practical situation short diametermeasures and goaftransporting tube and self-going rockbolt were adopted3. 1 Advance drillhole probing(42 steel tube and R32N, R25N were chosen as transWorking place stopped to excavate at 10 meters porting tube and rockbolt. Tubes and rockbolts werefrom coal measures 4 advance drillholes were arranged laid in three layers. The first layer had R32N self-go-n the working place in the front direction to find out ing rockbolts each rockbolt was 9 meters long and hadwhere the coal measures were located and their occur- 3-5 elevation angle. 42 steel tube was laid as thesecond layer, the reach tube was 9 meters long with 8Excavation in the working place stopped again at 5 12 elevation angle. In the third layer R25N self-goure. At the same time ,3 ing rockbolts were laid. Every rockbolt was 10 meterspredicting drillholes and 1 press-measuring drillhole long with 15-18 elevation angleere made to detect outburst hazard of coal measuresThe distance between the frame holes of the layersBy these drillholes the angle on the strike was 34 de- was 20 centimeters. Radial distance between the holesgree, inclined angle was 65 degree, coal measure was 20 centimeters, too. Frame hole diameter was 50thickness was 3. 4 meters and the angle between the millimeters. Cement and sodium silicate mixture wascoal measures and the center line of the tunnel was 85 grouted to fix surrounding rocks by rockbolts and tubesdegree. This angle should be so that coal measures and in the coal section. HG-A routin gastuff was blendedtunnel were almost perpendicularly intersected. The into the mixture. Steel frames at the intervals of 30nearest point where the tunnel touched coal measures centimeters were used to support the exposed parts ofwas YK33+750. 4. Coal measures had gentle outburst rockbolt and tube. This supporting structure is shownhazard by probing drillholes belonging to low gaseous in Fig. 1. Using the multi-layer supporting methodcoa measuresas wasdrained in advance through (42 steel tube and3. 2 Excavation style in coal measuresthe surrounding rocks were supported by grouting later.The coal-bearing series cut through by the tunnel Thus, water also was blocked outside the tunnel. ThisⅡwas a feasible supporting system to prevent gas,waterFor big excavation section( near 100 square meters ), and roof fallingmeasuresheading and bench driving method was selected as theVL中国煤化工 montoringstyle. The upper half-section was excavateCNMHGwere very important infirst as the heading section, till 20 meters after ptc. road tunnel excavation For the sake ofThis method was useful to lower half-section gas drain也球与环境第3期ensuring working safety during excavation in the coal nel building in the coal section. This information wouldsection and feeding back information of building, vari- be used for later construction and secondary supportous means of monitoring were applied in the whole tun- ing.R25N self- going rockboltR25N self-going rockbolt R32N self-g(42 draught tube(p42 draught tubeStell frameUnit: meterstructure through coal measures4. 1 Layout and measuring of the monitoring sec- survey steel arch set pressure The inner loop equip-tioment was used to survey secondary lining stress. ExceptThe western entrance of the right tunnel mileage secondary lining stress all measuring equipments werewas YK33 +750. 4. Three monitoring cross -sections set after blasting waste cleaning. The point where ewere arranged at YK33+742, YK33+752 and yk33 quipments were set was 2 meters long from the workin+762, respectively. They could measure the displaceplace. Furthermore equipment should be fixed up 4ment and stress. The layout of measuring lines and mediately after waste cleaning then information shouldFig. 2. One typical monitoring sec- be recorded before shotcreting. Information would betion was arranged at YK33 +751 and the measuring e- recorded once a day in the coming 15 days once twoquipment was arranged as shown in Fig. 3. The outer days from the 15th day to the 30th day once a weekloop equipment was used to survey shotcreting layer's from the 30th day to the 90th day and once a month af-radial stress. The middle loop equipment was used to ter the 90th da4.2 Monitoring results4.2.1InData progressing of YK33 +742, YK33+752 andYK33 +762 monitoring cross sections showed the basic3behavior of surrounding rock deformation. There werethree steps fast deformation slow deformation and ap2proximate stability. After excavation of lower half-section surrounding rock deformation and velocity muta-tedA-D: measuring linesRelations between deformation and time illuminate1-5: measuringthat bolting and shotcreting structure pressure andFig. 2. The layout of measuring lines and stakesgidity were stable and sage in the tunnel coal sectilisted in Table 1. The typical deformation- time relation curve is plotted in Fig. 42From these monitoring results the followingre presented中国煤化al stress and steel arch-eginning of supportingtheCNMHG1. Secondary lining stress indicatordecreased in the following days. These two parameterswould get stable after 40 days. They would keep stable3. Steel frame press indicatorand would not fluctuate violentlyFig. 3. The layout of stress indicator and pressure indicators第3期XIE Ye et al. : Monitoring in Building Road Tunnel Across Coal measures165This situation illuminated that the supporting sys- reached balanced condition while the supporting struc-tem, which consists of shotcreting layer-steel arch- ture deformation was in coordination with the deforma-rockbolt constrains the violent deformation at the betion of surrounding rockginning of surrounding rock movement. So the pressure2)In this supporting structure the secondary linof the supporting system appeared to increase. The sur- ing bore is low in pressure( about 0. 118 Mpa ) Thisrounding rocks formed a closed supporting structure by condition showed that preliminary supporting was safeinstalling of inverted arch. Thus the stress of support- enough. Secondary lining bore has no pressure basicaling structure appeared to decrease in some case. It ly and its effect is assistant supportinTable 1. Measured displacements of the tunnel through the coal sectionCross sectionHorizontal accumulativeMaximum contractive Arch top accumulativeArch top maximuncontractive valuevelocitysubsidence valueabsidence velocityYK33+7420.883,210.86YK33+7524213.240.8279Table 2. Measured stress and pressure of cross-section YK33+751Measured itemLeft walleft arch shoulderRight arch shoulderRight wallGrouting layer stress0.0810.06280.0760.1098steel frame stress0.1020.1150.0530.081l184. 2.2 Monitoring results of the typical sectionThe measuring data of shotcreting layer's radical5 Summarystress, steel arch set pressure are listed in Table 2. TheNow the Huayin Tunnel can pass through the coalcurves of stress/time relation are plotted in Fig. 5outburst goaf falling and water bursting were preventedning careful practice strict administration and thorough implementation of NATM. The engineering prac-Vertical displacementtice involving advance drillhole probing, multiple working cycle controlled blasting multilayer supporting andwhole stage monitoring could get positive effect in preventing gas outbursting surrounding rock falling andFig. 4. Curves of deformation and its ratewith time of cross-section YK33 +742water bursting. This engineering practice is useful toother tunnel construction across coal - section in roadRelation of frame pressure andtunnel project.-Relation of grouting layer stress and timeRelation of secondary lining stress and time100Fig. 5. Curves of stress and pressure with timof cross-section YK33 +751References中国煤化工1] Zhao Qianfu. Handbook of Coal Mine Safety[ M ] Beijing: Coal Industry[21 Tang Xiuyi. Forecasting and Preventing of Rock Outburst in Coal Mine[ m 1CNMHG[3] Wang Yanwu. Surrounding Rocks Measuring of Beiru Tunnel on Taijiu Exprehinese Journal of Rock Mechanics and Engineering998,172):148-152