International Conference on Advances in Energy, Environment and Chemical Engineering (AEECE-2015)

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1 International Conference on Avances in Energy, Environment an Chemical Engineering (AEECE-2015) Stuy on Damage Characteristic of Unergroun Cavern Blasting Excavation Base on Dynamic Damage Constitutive Moel Qian Dong 1, 2, a, Xinping Li 1, b an Hang Zhao 1,2 1 Hubei Key Laboratory of Roaway Brige & Structure Engineering, Wuhan University of Technology, Wuhan, China 2 School of Civil Engineering & Architecture, Wuhan University of Technology, Wuhan, China a ongqianse@126.com, b xinpingli@whut.eu.cn Keywors: Blasting amage moel, Damage criteria, Smooth blasting, Blasting parameters Abstract. The ynamic isturbance to the remaining surrouning rock mass of unergroun caverns prouce by blasting excavation can not be ignore. Consiering the rock mass amage inuce by compression-shear stress in the zone near the blasthole, the KUS ynamic amage constitutive moel was improve, an aing the efine amage iscrimination value to the KUS moel.using the improve KUS amage moel to conuct the numerical calculation of the Xiluou hyropower station left-bank unergroun powerhouse, to stuy the recommene smooth blasting parameters of sie wall protective layer rock mass of unergroun powerhouse. The results show that the amage epth of rock mass aroun the blasthole was influence by the cartrige iameter of blasthole, the increasing of the hole spacing only change the shape of the amage zone, an can not reuce the maximum amage epth.in engineering esign, the cartrige iameter of blasthole an the hole spacing can not be enlarge optionally, must be strictly in accorance with the requirements of the blasting esign. Introuction Traitional rock mass blasting amage constitutive moels such as GK, TCK, KUS, an YANG, which are all base on the expansion of micro cracks in rock mass uner the explosion shock loaing, an efining ifferent amage factors.but most of traitional blasting amage constitutive moels only consiere the rock mass amage cause by the tensile stress, it is not fully consiere the amage inuce by compression-shear stress in the area near by blasting source.therefore, the calculate amage range of the rock mass near the explosion impact loa is not accurate enough. On the basis of the TCK amage moel, Yang consiere the attenuation law of acoustic in the process of rock mass amage, an got a new moel of rock mass blasting amage,the moel was embee into the LS-DYNA3D ynamic finite element software[1].wang moifie TCK with the general bilinear an elastic-plastic constitutive, an embee the moifie moel into the ynamic finite element analysis software LS-DYNA, the rationality an accuracy of the moel were verifie by the engineering examples[2].li base on Yang-Liu amage moel, an took the amage variable into the elastic-plastic constitutive equation, stuie the amage range an criterion of Xiluou hyropower station unergroun powerhouse rock mass by numerical simulation metho an in-situ blasting vibration test[3].xiao couple the Mohr-Coulomb elastic-plastic constitutive an Yang-Liu rock mass amage moel, simulate the amage characteristics of a circular tunnel surrouning rock mass failure process[4].meng base on the blasting crater test, establishe the improve H-J-C rock mass blasting amage constitutive moel by consiering the amage cause by tensile stress,through the LS-DYNA software, stuy on blasting crater formation process[5].accoring to the measure ata of surrouning rock acoustic wave test, the KUS amage constitutive moel of rock mass was improve by RDA moel, it was showe that the numerical results of this moel was close to the measure ata[6]. In this paper, the KUS ynamic amage constitutive moel was improve, by consiering the rock mass amage inuce by compression-shear stress, an aing the efine amage iscrimination value to the KUS moel.therefore using the improve KUS amage moel to conuct the numerical The authors - Publishe by Atlantis Press 668

2 calculation of the Xiluou hyropower station left-bank unergroun powerhouse, to stuy the recommene smooth blasting parameters of protective layer rock mass of unergroun powerhouse sie wall. The establishment of the efine ynamic amage constitutive moel In this paper, an improve KUS amage constitutive moel was aopt, the computational theory an the framework of this constitutive moel was elastic-plastic constitutive equation of isotropic harening. In the elastic stage, the constitutive moel use generalize Hooke's law, the calculation formula as shown in Eq.1. E (1) Where,, are stress an strain of rock mass, E is the elastic moulus of rock mass. In the KUS amage constitutive moel, the tensile strength of rock mass is much less than the compressive strength[7]. Therefore, when the rock is in the three irection loaing, the micro cracks growth when the rock mass uner volumetric tensile stress, an calculation formula of crack ensity C as shown in Eq K 1 C km IC m (1 D) 2 C (2) P max Where, max is the maximum volumetric strain rate,, CP an K IC are the ensity, p-wave velocity an fracture toughness of rock mass, D is the amage factor of rock mass uner blasting loa, k, m are the material parameters.the mechanical parameters of amage rock mass as shown in Eq.3. 3(1 2) E E( 1 D) ; K K( 1 D) ; G K (3) 2(1 ) Where, K, G, K, G are the bulk an shear moulus before an after rock mass amage.the incremental Hooke law of rock mass contains the blasting amage as shown in Eq.4. K 2Ge (4) kk Where,, an e are stress, volumetric strain an eviatoric strain tensor respectively.the incremental theory of plastic mechanics was aopte after rock mass reache the yiel stage, by using isotropic harening criterion for etermining the plastic stress state of rock mass. In the rock mass area near blasting source, although the compressive strength of rock mass is much greater than the tensile strength, but the explosive loa near blasting source is in the large scale, will lea to the compression-shear amage of rock mass.base on a large amount of research works, the ratio of the principal stress ifference to the uniaxial compressive strength of rock mass was use as the iscriminant value F of rock mass amage egree as shown in Eq F (5) c Where, 1, 3 are the maximum an minimum principal stress of rock mass, c is the ynamic compressive strength of rock mass.in the efine ynamic amage constitutive moel of this paper, the iscriminant value F was embee in the efine moel through the FORTRAN language,an wrote in LS-DYNA program.the value F calculate at each loa substep in LS-DYNA program. Accoring to the safety vibration velocity stanar, the amage threshol C was erive,when the value of F excee the value of amage threshol C,it can be consiere rock mass into the compression-shear amage state, an each moulus got further reuce in Eq.3 as shown in Eq.6. E C E, K C K, G C G (6) f f f Where, C is the reuction factor,the calculation formula as shown in Eq.7. f 669

3 C f 1, F F C 1 C a, F C Where,the value F calculate at each loa substep in LS-DYNA program,the value of C an are 0.3 an 0.2 accoring to numerical calculation. The amage law of unergroun powerhouse protective layer uner blasting excavation Accoring to the excavation ata an spatial imension of unergroun powerhouse protective layer,the numerical moel was establishe as shown as in Fig 1 an 2. (7) Fig.1 Application of in-situ stress an constrains Fig.2 Sketch of numerical moel The whole numerical moel is meshe into D soli164 elements, an ue to the symmetric of numerical moel, in the numerical calculation, it only nee take half of the moel to be calculate. Symmetric bounaries are applie on the symmetry planes, an non-reflective bounaries are applie to the other outer bounary.the material parameters of rock mass in iversion tunnel groups is shown in Table 1. Elastic Tangent Cohesive Friction Compressive Poission s Density moulus moulus strength angle strength ratio 2700kg/m 3 50GPa 8GPa 2.6MPa MPa 0.25 Table 1 Dynamic material parameters of rock masses In the C-J conition,the average pressure of explosive etonation, for the ecoupling charging boreholes, the calculation formula of explosive pressure as shown in Eq D c l e p 0, pm p n 2(1 ) b l 0 (8) b Where p 0 represents average pressure of explosive, 0 is the ensity of explosive material, D is the etonation velocity, is explosive constant,usually takes 3. p m represents maximum explosive pressure on the wall of blasthole in ecoupling charging conition, c is the charge iameter, b is the borehole iameter, l e is the length of grain, l b is the charging length of blast-holes. n is a pressure enlarging coefficient. Accoring to the in-situ blasting parameters:etonation velocity an ensity are 3600m/s, 950 kg/m 3, charge an blasthole iameter are 25 mm an 50 mm respectively. It s assume that l e is equal to l b, then p m can be calculate to 320.4MPa, an the measure in-situ stress was 10 MPa. The numerical calculation time is 1s, in which the in-situ stress is applie on the rock mass structure in the whole calculation process, an the blasting loa is applie to the time perio of s, the time of 670

4 peak blasting loa is s, an the loaing curve is shown in Fig.3.The layout of smooth blastholes in numerical moel as shown in Fig.4. Fig.3 Loaing curve of blasting loa an in-situ stress Fig.4 Layout of the smooth blastholes In orer to stuy the influence of ifferent charge iameter of blasthole on the amage range of surrouning rock, four ifferent conitions were carrie for the contrast analysis, the blasthole spacing was kept as a constant 0.5m in the numerical simulation.the blast loas applie on the smooth blasthole in four ifferent conitions are respectively 160, 320, 640, an 960MPa an corresponing charge iameter are 22, 25, 28, an 30 mm, the number of conitions is from 1 to 4. The istribution figment of the value F in surrouning rock mass as shown in Fig.5. (a) conition 1 (b) conition 2 (c) conition 3 () conition 4 Fig.5 Distribution of the value F in surrouning rock mass Combine with the previous conclusion that when the value of F excee 0.3, the rock mass reache the amage stage.the Fig.5 shows that the amage area were locate aroun the smooth blasting holes, an eepen with the increase of charge iameter. The amage epth ata of various parts of the surrouning rock are shown in Table 2. Table 2 Damage epth of surrouning rock masses Charge iameter(mm) Depth of amge(m) Wall corner Mile of sie wall Arch foot

5 When the blasting loa is constant, the maximum amage epth locate in the arch foot of surrouning rock mass, an with the increasing of charge iameter, the amage epth of arch foot increasing rapily than other part of unergroun powerhouse. In orer to stuy the influence of ifferent blasthole spacing on the amage range of surrouning rock, two ifferent conitions were carrie for the contrast analysis, the blasting loa was kept as a constant 320MPa in the numerical simulation.the blasthole spacing are respectively 0.5 an 1m.The istribution figment of the value F in surrouning rock mass as shown in Fig.6 an Fig.7. Fig.6 Distribution of the value F in surrouning rock mass with 1m blasthole spacing Fig.7 Distribution of the value F in surrouning rock mass with 0.5m blasthole spacing By comparing the ifferent numerical results of blasthole spacing 0.5m an 1m, it foun that the blasting amage range is extene from the center of smooth blasthole.when the hole istance increases, the amage area is serrate, an the amage epth of the two conitions is approximately the same, but the shape of amage area is ifferent. Conclusion The amage epth of the smooth blasting excavation is controlle by the iameter of the charge, although the increase of the hole istance can control the shape of the amage area, but the istribution an epth of the amage area is increase, which is not conucive to the stability of surrouning rock. Acknowlegements This work was financially supporte by the National Natural Science Founation of China ( ). References [1] YANG Jun, JIN Qian-kun. Explosion an Shock Waves. Vol. 20(3)(2000), p (in Chinese) [2] WANG Zhi-liang, ZHENG Ming-xin. Rock an Soil Mechanics. Vol. 29(1)(2008), p (In Chinese) [3] LI Xinping, CHEN Junhu, LI Youhua, et al. Chinese Journal of Rock Mechanics an Engineering. Vol. 29(10)(2010), p (In Chinese) [4] ZUO Shuang-ying, XIAO Ming, XU Jian-ke, et al. Rock an Soil Mechanics. Vol.32(10)(2011), p (In Chinese) [5] MENG Zhuo-chao, ZHOU Ke-ping. Journal of Central South University(Science an Technology). Vol. 43(7)(2012), p (in Chinese) [6] HU Ying-guo,LU Wen-bo,CHEN Ming, et al. Rock an Soil Mechanics. Vol.33(11)(2012), p (In Chinese) [7] KUSZMAUL J S. Proceeings of the 2n International Symposium on Rock Fragmentation by Blasting. Canaa: Keystone, 1987: