Numerical Analysis of Effect of Water on Explosive Wave Propagation in Tunnels and Surrounding Rock

Sept. 2007Jourmal of China University of Mining & TechnologyVol.17_ No.3Available online at www.sciencedirect.comSCIENCE@)DIRECT.J China Univ Mining & Technol 2007, 17(3): 0368 -0371Numerical Analysis of Effect of Water onExplosive Wave Propagation inTunnels and Surrounding RockXIA Chang-jing, SONG Zhen-duo, TIAN Lu-lu, LIU Hong-bin, WANG Lu, WU Xiao-fangSchool of Mechanics & Civil Engineering, China University of Mining & Technology, Beijing 100083, ChinaAbstract: Based on the application of practical engineering, propagation processes of explosive waves in rock withwater well and tunnel are simulated by ANSYS/LS-DYNA software. The evolution of damage in rock is presented. Theeffect of water on the damage of the concrete slab in a tunnel is compared with damage inflicted without water. Thenumerical simulation ilustrates that water plays an important role in the evolution of damage of the concrete slab in amine tunnel. In the presence of water in the rock the concrete slab is damaged more severely than without water in rock.The effect of water location in the rock is also considered. It is found that the concrete slab in the tunnel shows variousdegrees of damage as a function of the different locations of water. Attenuation laws of stress waves over time-space inrock with water are also obtained. Numerical results indicate that, under blast loading, there are three zones in the rock:a crushed zone neatby the explosive charge, a damaged zone and an elastic zone. The conclusions of numerical analysismay provide references for blasting designs and structure protection.Key words: explosive wave; numerical simulation; concrete slab; damage evolutionCLC number: 0381; TU 458.31 Introductionthat the tunnel's behavior of resisting the impact fromground shock waves is affected by the configurationExplosions over short distances are harmful to ex-of the tunnell. Liu suggested a method which takesiting tunnels, which are major problems in practicalthe incident wavelength, the tunnel diameter and theprojects. Many recent accidents of water penetratingdistance between charges and tunnel surface into ac-nto tunnels have occasioned heavy losses due tocount to determine the dynamic stress concentrationnearby blasting. It is therefore important to study thefactor on the surrounding rock facing the charge bypropagation of explosive waves in rock with tunnelsnumerical simulation and dynamic photo-elastic ex-under conditions of blast loading. But it is a difficultperiments'. Zhao et al used the coupled method ofproblem to solve because there are complex factorsUDEC to simulate the propagation of blast waves inaffecting this problem. including the explosive charge,the jointed rock mass and found joints in rock aredifferent media, the tunnel itself (its configurationconducive to the attenuation of explosive waveso.and materials), etc.Smith maintained that the use of rough-walled tun-During the last decade, a sizeable body of pub-nels could offer a means of providing an efficientlished work has appeared relating to explosive waveprotective entrance to a sensitive structurel9!.propagation in rock and safety problems of tunnelsAlthough these earlier works presented havebecause of nearby blasting'Liu summarized theachieved significant progress, they do not satisfy ourpresent situation of the effect of nearby blasting on aneeds with respect to theories and methods to solvetunnel and pointed out the weaknesses and problemspractical Droblems. Based on the experience in Chinawhich need to be studied furtherl'. Xia et al foundof ar中国煤化工:ration in the sub-Received 18 Sepiember 2006; acepted 16 January 2007fHCNMHGProjects 2002CB412705 supported by the National Basic Research & Development Program (973), 50579042 by the National Natural Science Foundationof China, NCET-05-0215 by the Chinese New-Century OUutstanding Fellowship and JD102900553 by the Key Laboratories of Beijing Municipal Commis-sion of Education and Science and Technology CommissionCorresponding author. Tel: +86- 10-62331286; E-mail adress: xiacj@cumtb.edu.cnXIA Chang-ing etalNumerical Analysis of Effect of Water on Explosive Wave Propagation in ...._369floor of a mine tunnel caused by nearby blasting, weThe JHC model is employed to facilitate a full simu-simulated the process of explosive wave propagationlation of stress wave propagation in rockt .in rock with water and a tunnel using ANSYS/LS-The JHC model is described asDYNA software.σ° =[A(1-D)+ BP"~][1+CIn(e ")],2 Numerical Simulationwhere D is the damage (0≤D≤1), p'=PIf'the normalized pressure (where P is the actual pres-2.1 Numerical modelure, f' the quasi-static uni-axial compressiveWe simplified the problem as a two-dimensionalstrength) ande° =e1ε。the dimensionless strain rate(where ε is the actual strain rate and E = 1.0s-plane strain model.Fig. 1 shows the overall configuration and the sizethe reference strain rate). A, B, C and N are the mate-rial constants.of the numerical model.The radius of the explosive charge is 175 mm. TheParameters of the materials used in the calculationdistance from the explosive charge to the concreteare listed in Tables 1-3.slab is 9500 mm. The water well is 8500 mm longTable 1 JWL equation of state parameters ofTNT usedand 600 mm wide and the distance between the waterPwell and the charge is 6000 mm. Because of the com-(gcm) (m/s)(GPa) (GP2) (GPa) Ri Rz_“(GPa)plex distribution of the multi-hole strip explosive1.566700 22.25 650.0 9.25 4.2 1.1 3.4 8.5charge, it was simplified as a single-hole explosivecharge as suggested by Henrych in 197910.Table 2 Parameters of rock materialf'(g/em)Smxs (GPa)DIDrHc μ (GPa) (GPa)2.680.160 7.0 14.86 0.04 1.0 0.001 0.10 0.0160.80RI75Table 3 Parameters of concrete material800000: 5000p(g/em)E(GPa)o,(MPa)e9500 .600035.70.2014.00.003Fig. 1 Sketch of the explosive charge and tunnel construction3 Analysis of Numerical Results1. Water well; 2. Concrete slab; 3. Rock;4. Tunnel; 5. Explosive charge (Unit: mm)3.1 Stress wave propagation in rockFig.2 shows the propagation of stress waves in2.2 Model and parameters of the materialdifferent locations in rock when the distance of theIn our study, the JWL state equation has beenwater is 6 m from the charge. The peak value of stressadopted to describe the. behavior of the explosionwave reduces rapidly near the charge while it reducesproduct of TNT charge'. Because the concrete slabslowly far from the charge. At a distance of 1.0R (R isis in the area beyond a certain scaled range, the elas-the radius of the explosive charge) from the chargetic plastic model is applied to describe the damagecenter the stress peak is 2 GPa, while at a distance ofprocess and fragment formation induced by the stress7.0R the stress peak is not more than 200 MPa.wavel2l. The null material model is selected for water.2250p300r一x11.0R2000-501750x-25.0OR1500... x-2.0R125050-1000x=5.0R .750.... x=7.0Rs00中国煤化工常00.0.8.21.CNMHGTime (msYH细) Low distance(b) High distanceFig. 2 Stress waveform at dfferent locations from the charge in rockJoumal of China University of Mining & TechnologyVol.17 No.33.2 Damage evolution in rockfrom the charge in rock is larger than 11.8R, the ac-Fig. 3 presents the accumulated damage evolutioncumulated damage value is smaller than 0.02 whichof rock in different locations when the distance of thecan be ignored. According to the accumulated dam-water is 6 m from the charge. It can be seen that theage in the closed basting, the damage can be dividedaccumulated damage value of rock is different in dif-into three rock zones: the crushed zone where D isferent locations. Near the explosive charge, the ac-equal to 1 (2.3R≤x≤3.1R), the damage zonewhere D is smaller than 1 but larger than zerocumulated damage value is 1, i.e, the rock is crushed.(2.3R≤x≤11.8R). The elastic zone is the zoneWith the propagation of stress waves in rock, the ac-further than 11.8R from the charge.cumulated damage value decreases gradually. Beyonda certain scaled range, the rock is not damaged but.3 Effect of water on concrete slab damageexperiences elastic deformation. When the distanceIn order to analyze the effect of different locationsx-3.1R1.of water on the concrete slab damage, the distancesbetween water and the charge in the numerical simu-x3.8R0.8lation are chosen as 7, 6, 5, 4 and 3 m, respectively.From Fig. 4, it can be seen that the concrete slab inthe tunnel shows various degrees of damage given thedifferent locations of water in the rock. The reason isthat with different locations of water the strength of0.the reflected wave is different. Fig. 5 also shows thatthe second pressure peak varies in different cases.When the blast operation is near the water, the opti-Time (ms)mal location of the explosive charge should be takenFig. 3 Accumulated damage evolution of rock at dfferentinto consideration in order to realize the expectedlocations from the charge(a) Distance of waler is 7 m from the charge(b) Distance of water is 6 m from the charge(C) Distance of waler is s m from the charge(d) Distance of water is 4 m from the charge中国煤化工(e) Distance of water is 3 m from the chargeYHCNMHGFig. 4 Damage of concrete slabXIA Changjing etalNumerical Analysis of Effect of Water on Explosive Wave Propagation in ....371ing was studied through numerical simulation. The_ Without waternumerical results indicate that under blast loading.. Distance-7m。 Distance-6mthere are three zones in the rock: the crushed zone. Distance 5mnear the explosive charge, the damage zone and theDistance-4melastic zone. The range of each zone is indicated.， ... Distance=-3mWater greatly affects damage to the concrete slab.2The concrete slab, in the case when water is presentin the rock, is far more damaged than without water.Different degrees of concrete slab damage are pre-sented when the distance of the water location fromTime (ms)the charge varies in the rock. The conclusions of ourFig. 5 Pressure-time history in the middle of concretenumerical analysis may provide reference values forslab in different casesblasting designs. Numerical methods can be used toevaluate the safety of tunnels in the case of nearby4 Conclusionsblasting.The behavior of rock and tunnels under blast load-ReferencesLiu H. Study progress of influence of nearby blasting on a tunnel. Blasting, 1999, 16(1): 57- -63. (In Chinese)2] Wang Q H, Shen J H, Wei H. Analysing the failure efect of tunnel under the act of blast impact wave. The Chinese Joumal ofGeological Hazard and Control, 2000, 11(3): 67- -69. (In Chinese)3] Xia z X, Miao X X, Mao X B. 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