Papers by Keyword: Hard Rock

Abstract: The shield tunneling construction would cause the buried pipeline deformation. In order to predict the influence to the buried pipeline when shield tunneling crossing the thick and hard strata, taking 201 contract section shield tunneling of Dalian Metro construction as the research object, the buried pipeline deformation effects are analyzed. Firstly, the shield tunnel excavation and support simulating model is constructed basing on Flac3D technique. Secondly, the ground settlement and its influence to the buried pipeline are analyzed with finite difference digital computation. According to the simulation for the shield tunneling crossing the thick and hard riverbed, the settling volume of the ground, the deformation modes and degrees of the buried pipelines are discussed to reveal the deformation rules. Results show that the deformations of two groups of measuring points tend to be uniform; the excavation process includes the stabilization period, the critical point and the deformation period in 50m long simulation model; the drainpipe appears deformation from three directions, and the severity of deformation mainly comes from the vertical direction settlement.

Abstract: In this paper, a series of true triaxial tests indoor with acoustic emission mornitoring were conducted and the characteristics of acoustic emission rate and energy releasing rate in the section adjacent to failure were gained. According to the different characteristics of acoustic emission rate, we divided the events rate into three types which were main shock, foreshock-main shock and cluster shocks. And then, a prediction method for hard rock was put forward according to different events rate types based on the trends of AE signals in the section adjacent to failure for hard rock.

Abstract: it is already confirmed that the rock mechanical characteristics under unloading condition differ from those under load condition, and the excavation process should be considered to be a typical kind of unloading mechanical behavior. As thus, a series of representative unloading tests and shear strength tests about unloading cracks are performed on hard granite samples from the underground workshop excavation zone in Dagangshan hydropower station in western China, where the surrounding rock is affected by high geo-stress. Based on the tests results, some significant theory research is made.

Abstract: Rock roadway digging machine is generally applicable to soft mudstone, sandy mudstone roadway. When it comes to the harder rock,, the speed of digging machine construction is greatly reduced, the tool were wear seriously, the service life is substantially reduced, the tunneling cost is dramatic increased. So we must use the loose secondary blasting, to soften rocks. According to the specific circumstances of the west lane in Liuzhuang Coalmine, and proposed coal mine loose blasting technique program in keeping with construction requirements after the study, that is reasonable blast-hole depth, hole parameters, charge amount, charge structure, stemming length. Research results have a good loose blasting effect in engineering practice.

Abstract: With the rapid development of urban construction, the shield construction technology has been greatly developed. Shield tunneling method generally adapts to relatively uniform soil, soft rock and sand rock strata, and the shield tunnel construction has been more mature for the homogeneous strata. However, for the soft and hard interbedded strata, how to solve the problems of breaking the hard rock, increasing the tunneling efficiency and reducing the construction costs, are difficult problems in the shield tunnel construction. In this paper, based on a great deal of theoretical analyses and engineering practices, the effective methods of improving the efficiency of tunneling, reducing cutter wearing and decreasing the construction costs in the process of the shield tunneling construction in hard rock and gravel layer are proposed.

Abstract: In the process of deep tunnel excavation, the surrounding rock mass, which often endures high initial geo-stress, is in the state of typical unloading. As the adjustment of stress induced by excavation, rock mass behaves a peculiar kind of mechanical deformation characteristics, different from those in loading conditions. As thus, a series of representative unloading tests on hard granite from DaGangShan power station in China, which is being excavation at 1500 meters deep below earth surface, are carried out to simulate dynamically excavation process for studying the peculiar mechanical deformation characteristics. On the basis of unloading tests, a series of research results are acquired as follows： (1) Under unloading condition, lateral deformation occurs in the unloading direction and volumetric strain changes from compression deformation to dilation deformation. (2) Under unloading condition, hard granites behave brittle failure and Mogi-coulomb criterion can well describe the failure characteristics. (3) According to curves of unloading tests, the constitutive model is deduced for simulation analysis.

Abstract: Rock burst hazard is the main problem of hard rock deep tunnel under high ground stress conditions. The prevention logic of prevention and control of rock burst is proposed by combining local energy release rate index based on the brittle Hoek-Brown model. Stress releasing holes are adopted to lead some energy to release actively and eliminate burst potential of rock burst. Supporting opportunity and parameters were studied by contrasting the magnitude of released energy in FLAC3D numerical software, and then the prevention logic of rock burst is presented. Stress releasing holes relieve stress concentration of the working face, transfer the stress to the deep and reduce the risk of rock burst near the working face. At last, the prevention and control of rock burst for sinping II Hydropower tunnel was analyzed, the results are in good agreement with the actual situations. The proposed method could benefit other deep tunnel projects which have brittle failure.

Abstract: DaGangShan power station in China is being excavation at 1500 meters deep below earth surface, where the surrounding rock is affected by high initial geo-stress. Deep excavation of rock tunnels causes release of high initial geo-stress and produces unloading action. As thus, a series of representative unloading tests on hard granite from DaGangShan power station are carried out to simulate dynamically excavation process, and in unloading tests, the stress path of decreasing confining pressure along with increasing axial pressure is accepted. The results of tests show as follows: (1) Under unloading condition, lateral deformation occurs in the unloading direction and volumetric strain changes from compression deformation to dilation deformation. (2) Under unloading condition, crack deformation appears, which results in Poisson’s ration rise and deformation modulus decrease. (3) Under unloading condition, hard granites behave brittle failure and Mogi-coulomb criterion can well describe the failure characteristics.