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  --2019, 38 (12)   Published: 01 December 2019
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2019-12期目录
 2019, 38 (12): 2377-2377
Full Text: [PDF 154 KB] (230)
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Research progress of coal roadway support technology at home and abroad Hot!

SHAN Renliang1,PENG Yanghao1,KONG Xiangsong1,XIAO Yuhang1,YUAN Honghu1,
 2019, 38 (12): 2377-2403 doi: 10.13722/j.cnki.jrme.2019.0386
Full Text: [PDF 983 KB] (304)
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This paper briefly summarizes main achievements in the field of coal roadway support in China and expounds the research status of coal roadway support technology abroad. In recent years,the support technology of coal roadways in China is mainly a variety of single or combined support systems developed around bolting support for solving the emerging new problems of coal roadway support sites,foreign coal roadway support systems are diverse which have brought beneficial inspiration for the improvement and diversified development of coal roadway support theory,equipment and technology research in China,especially for surrounding rock control of coal roadways in deep coal mines with a depth more than 1 000 m. In this paper,the support of coal roadways was deeply studied by means of theoretical analysis,model test,numerical simulation and field test,and the support theory and technology of strengthening sidewalls and corners,composite support technology of longitudinal beams,cooperative support technology and shear-resistant anchor C-shaped tube cable(ACC) support technology in coal roadways were proposed,for realizing bolt and cable integrated(collaborative) support. In addition,based on the physical model test device of dynamic pressure roadway support developed,the simulation technology of coal roadway support was improved,and the innovation points,application conditions and significance,existing shortcomings and improvement directions of each technology were discussed. Finally,based on the above research results,the development trend and suggestions of coal roadway support technology in China were put forward. In the future,the support technology of coal roadways will adopt diversified methods such as the combination of multiple active support technologies or the combination of active and passive support technologies,and gradually develop to the direction of intelligent support.

Rock damage evaluation based on wave velocity field imaging technology#br#

ZHANG Yanbo1,WANG Kexue1,YAO Xulong1,HUANG Yanli2,SUN Lin1,LIANG Peng1,TIAN Baozhu1,LIANG Jinglong3
 2019, 38 (12): 2404-2417 doi: 10.13722/j.cnki.jrme.2019.0497
Full Text: [PDF 984 KB] (219)
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Based on acoustic emission regional wave velocity imaging technology,acoustic emission detection experiments in the process of rock cracking were carried out. The effect of acoustic emission wave velocity imaging technology was examined in terms of the accuracy of damage state detection and the process of rock damage evolution. A damage evaluation system was constructed and a damage variable related to acoustic emission wave velocity field was established. The results show that the spatial location of the damaged area can be accurately described by the regionalization of the velocity imaging nephogram. The weakening area around the low wave velocity can represent the future development direction of cracks. The discrete distribution of high and low wave velocities can depict the real state of rocks. The evolution process of the nephogram reveals that the key fracture damage of rocks occurs mostly at abnormal areas of the wave velocity or their junctions and,around them,the low wave velocity area gathers,expands and penetrates into the whole rock. An evaluation system of feature extraction,determination of weight and comprehensive evaluation by TOPSIS method was proposed for assessing the damage state of rocks. It is also shown that,under multi-stage loading,the rock undergoes a stable and accelerated damage development and that the damage decreases temporarily due to crack compaction in the stage of the accelerated damage development. This evaluation method,which can quantitatively describe the damage state and show the damage distribution area at the same time,has a remarkable effect on the characterization of micro-fracture behavior and great significance for the evaluation of rock damage state.

Experimental study on leaf vein bionic gas drainage of multi-branch#br# horizontal wells in coal seams#br#

GUO Xiaoyang1,DENG Cunbao1,2,FAN Yongpeng3,FAN Nan3,MU Yongliang3
 2019, 38 (12): 2418-2427 doi: 10.13722/j.cnki.jrme.2019.0696
Full Text: [PDF 1547 KB] (59)
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In order to improve coalbed methane recovery in low permeability coal seams,a concept of leaf vein bionic gas drainage of multi-branch horizontal wells was proposed. Vein structure of 4 typical leaves was extracted and analyzed by leaf specimen scanning and structural measurement. The fluorescent labeling experiment was used to study water transport in vein structureand to obtain the bionic features. The physical simulation experiment was carried out by self-developed experimental system to study the influence of leaf vein bionic characteristics on flow-temperature field. The results show that the extraction effect is better with asymmetrical branches and is most affected by the length of branch wells. When the length of branch wells increases by 50%,the gas pressure decreases by 28.37% in the reservoir. Increasing the angle of branch wells can significantly enhance the gas pressure relief. When the distance between the branch wells increases by 50%,the gas pressure decreases by 6.81%. Temperature change lags behind the pressure in the reservoir. The decreases of both the gas pressure and the temperature are positively correlated with the initial gas pressure in the early stage of gas extraction but hardly affected by the initial gas pressure in the later stage.

Study on the strength evolution rule of surrounding rock mass in roadways#br# based on the in-situ borehole shear method

JING Hongwen,SU Haijian,SHI Xinshuai,ZHAO Zhenlong,MENG Bo
 2019, 38 (12): 2428-2437 doi: 10.13722/j.cnki.jrme.2019.0495
Full Text: [PDF 473 KB] (88)
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The in-situ test is the most direct and accurate method to collect the strength and deformation parameters of engineering rock mass at present,which has a significant reference value to the support design and stability control of underground engineering. In this paper,the testing theory,method,applicability and boundedness of ultrasonic exploring method,borehole penetrating method and borehole shear method for testing the in-situ strength of surrounding rock mass in underground roadways were systematically discussed. Both the ultrasonic exploring method and borehole penetrating method rely on the verification and calibration of empirical formula or laboratory test results to some degree,while the borehole shear method absolutely depends on the in-situ testing. The borehole shear method is also appropriate for the surrounding rock mass containing closed or small opening fractures. Therefore,the obtained in-situ strength parameters by the borehole shear method can be served as a comprehensive index to evaluate the stability of surrounding rock mass in roadways. Based on the in-situ cohesion and internal fraction angle tested from the borehole shear method,the uniaxial compression strength can be obtained according to the linear Coulomb criterion. Finally,based on lots of testing results of Pingdingshan mining area and Datong mining area by the authors? team using the borehole shear method in recent years,some topical cases were analyzed and discussed about the spatial distribution and the effect of excavation time of in-situ strength of surrounding rock mass in roadways,strength distribution feature in the coal-rock interface,and the effect of upper coal pillar on the strength of surrounding rock mass. The research results show that,with an increase in testing depth,the cohesion and uniaxial compression strength of surrounding rock mass of Dinger rail roadway in Pingdingshan #9 coal mine,increase gradually and present the spatial distribution feature of an exponential function. The in-situ strength of engineering rock mass also has the excavation time effect. The cohesion and uniaxial compression strength of surrounding rock mass of Wujiu new special roadway in Pingdingshan #4 coal mine after excavation for three months are obviously smaller than those of fresh excavation roadways. The in-situ strength of sandstone in the roof of 5937 roadway in Xinzhouyao coal mine of Datong mining area is larger than that of the coal seam,and the strength of rock mass in the coal-rock interface is between them. The 5704 roadway of Xinzhouyao coal mine is affected by both the neighboring goaf of this working face and the coal pillar of the upper goaf,resulting in the strength difference between two walls,as well as the strength difference of surrounding rock mass with different positions below the pillar.

Study on the propagation mechanisms of shale fractures #br# under direct shear conditions

HENG Shuai,LI Xianzhong,LIU Xiao,ZHANG Xiaodong
 2019, 38 (12): 2438-2450 doi: 10.13722/j.cnki.jrme.2019.0557
Full Text: [PDF 804 KB] (198)
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In order to deeply understand the propagation mechanisms of shear fractures and directivity effect of bedding,direct shear tests were performed on Longmaxi shale specimens with various bedding orientations with respect to the loading direction under different normal stresses to study the fracture propagation patterns. The evolution process of nucleation,propagation and coalescence of en-echelon fractures and directivity effect of bedding were investigated. The results show that,due to the shear-induced tensile stress,en-echelon micro-cracks are generated around the shear plane,further develop,connect and finally form a macroscopic shear fracture zone with a uniform width and obvious heterogeneity. For layered shale,the shear-induced en-echelon cracks typically develop along the bedding plane. The cracking degree and orientation of the en-echelon cracks are closely related to the bedding orientation,showing significant bedding directivity effect. It is very difficult to induce en-echelon cracks in the direction oblique to the bedding plane along which the shear force is exerted. When the angle between the shear direction and the bedding plane is 30° or 60°,the en-echelon cracks are generated along the bedding plane,especially for 30°. When the shear force is exerted normal to the bedding plane,weak bedding cracking could still be observed to some extent. The shear fracture surface formed by the coalescence of the en-echelon fractures often presents a serrated shape and occurs striation and abrasion in post-peak frictional sliding stage. However,the normal stress could obviously inhibit the formation of en-echelon cracks and make the shear plane smooth. When the shear force is exerted at a certain angle to the bedding plane,complex fracture morphology is formed by the shear induced bedding-parallel en-echelon fractures. The complex fracture morphology is mostly confined to the shear fracture zone,showing obvious localized deformation.

Explosion energy transmission and rock-breaking effect of in-hole dual initiation

LENG Zhendong1,2,FAN Yong1,LU Wenbo3,GAO Qidong3,ZHOU Junru3
 2019, 38 (12): 2451-2462 doi: 10.13722/j.cnki.jrme.2019.0474
Full Text: [PDF 732 KB] (85)
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In the process of rock fragmentation by blasting,the initiation mode has an important influence on the energy transmission and rock-breaking effect. The accumulated energy effect by collision of two oppositely traveling in-hole detonation waves was proved theoretically,and the energy transmission characteristics under the condition of dual initiation were analysed. The rock-breaking scopes under different initiation modes were calculated adopting a tension and compression-shear statistical damage model,and the fragmentation size distributions under different initiation modes were also investigated by comparing the field test results of bench blasting. The results show that when the two in-hole detonation waves collide in the middle of the borehole,the pressure near the collision point is greater than the sum of the strength of the two detonation waves and the local rock fragmentation degree is significantly improved. Under the condition of dual initiation,the volumes of tension and compression-shear failure zones of rock mass near the borehole are larger than those of bottom,top or middle initiation. When the initiation point position of in-hole dual initiation is changed,the volume of the compression-shear failure zone changes little but the volume of the tension failure zone changes obviously. Therefore,through reasonably designing the location and quantity of the initiation points,the spatial distribution of explosion energy can be adjusted by the collision of detonation wave and shock wave to improve the fragmentation degree of local rock and to meet different engineering requirements.

Three-point bending test study on the propagation law of internal cracks and failure characteristics of brittle solids based on 3D-ILC technology#br#

WANG Haijun1,LI Hanzhang1,2,REN Ran3,TANG Lei1,YU Shuyang1,2,ZHANG Zhitao1
 2019, 38 (12): 2463-2477 doi: 10.13722/j.cnki.jrme.2019.0358
Full Text: [PDF 1354 KB] (76)
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Crack propagation in rocks is one of the important issues in geotechnical engineering. Based on 3D-ILC technology,an ideal brittle material is selected,and the actual internal crack with arbitrary parameter is generated without affecting the surface of the sample. The three-point bending test of ideal brittle material samples containing actual random internal cracks generated without changing the sample surface was carried out and compared with the complete samples. Failure process,characteristic load,failure mode,fracture characteristics,dynamic bifurcation and stress moire were analyzed,and the K-distribution and extension path of the crack tip were obtained by numerical simulation. The results show that the cracking and breaking loads of the specimen are reduced greatly due to the existence of internal cracks,and that the internal crack tip presents petal-like strain moire which can be monitored by the stress birefringence technology combined with 3D-ILC. Under three-point bending,the blank specimens occur dynamic fractures with atomization,feather zone characteristics caused by dynamic crack bifurcation,while the crack-containing specimens gradually crack from the lower tip to the upper tip of the internal crack of a pure type–I failure in a drop-like shape with characteristics of the intersection Wallner line. It is also indicated that both the K-distribution at the crack tip based on M-integral and MTS-based internal crack propagation path simulation are consistent with the test results. Compared with the current mainstream methods in the study of transparent rock,3D-ILC has certain advancement in brittleness,crack authenticity,stress field visualization and fracture characteristics. The test and numerical simulation results will provide experimental and theoretical references for research on problems including internal crack propagation and three-dimensional fracture of brittle materials such as rock.

Study of propagation behaviors of mode I cracks under blasting stress#br# wave based on RPC specimens

WAN Duanying1,2,ZHU Zheming1,2,LIU Ruifeng1,2,LIU Bang1,2,LI Jianfei1,2
 2019, 38 (12): 2478-2490 doi: 10.13722/j.cnki.jrme.2019.0573
Full Text: [PDF 1867 KB] (45)
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In order to study dynamic propagation of mode I cracks under blast loads,a rectangle plate specimen with a crack,prepared by PMMA with good homogeneity and transparency,was proposed in this paper. The experimental system consists of a high dynamic strain amplifier,an oscilloscope,a constant source,strain gauges and crack propagation gauges. The strain gauges and crack propagation gauges(CPGs) were used to measure the blast load and crack propagation speed respectively,and the scanning electron microscope was applied in studying the property of the fracture surface. AUTODYN was applied in simulating crack dynamic propagation behavior. The JWL equation of state(EOS) and a linear EOS were respectively applied to describe the explosive detonation products and the relationship between the pressure and density of PMMA. A modified principle stress failure criterion was employed to assess the material state. Based on displacement extrapolation method,a numerical model was established in ABAQUS code to acquire dynamic stress intensity factors at the crack tip. The experimental and numerical results show that the propagation of mode-I cracks under blast stress wave can be divided into stable propagation and unstable propagation stages,Fracture surface roughness will decline with crack propagation in the stable propagation stage and fracture surface is relatively smooth in the unstable propagation stage. It is also revealed that crack propagation velocity varies in a certain range in the stage of crack stable propagation.

Shaking table test research of the influence of voids on seismic#br# responses of tunnel structures

YAN Gaoming1,SHEN Yusheng1,XIN Chunlei2,3,GAO Bo1,ZHOU Pengfa1,ZHANG Xi1,YANG Jiaqi1
 2019, 38 (12): 2491-2501 doi: 10.13722/j.cnki.jrme.2019.0547
Full Text: [PDF 1310 KB] (59)
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A large shaking table model test was carried out to investigate the dynamic response of the tunnel lining with a void behind the crown,and the test results were discussed based on the acceleration response characteristics,strain response characteristics and damage patterns of the tunnel lining under vertical ground motions. Combining with the Fourier spectrum and the frequency transfer function,the spectrum characteristics of the lining structure were demonstrated. The results show that the vertical ground motion mainly affects the crown,arch springing and invert of the lining with or without voids. The voids increase the peak value of the acceleration response of the tunnel while have no influence on the characteristic of the acceleration response. The larger the input peak ground motion is,the more significant the effect of voids on the acceleration response of the lining structure is. The existence of voids does not change the spectral characteristics of the structural response. The main frequency component of the lining structure is excited under earthquake action,and the 1st and 2nd dominant frequencies at the lining reflect the seismic properties of model soil and lining structure respectively. The void behind the crown changes the stress states of the crown and arch springing of the lining. For the lining without voids,large tension strains appear at the crown and invert while large compression strains occur at the arch springing. In the case of the lining with voids,however,large tension strains appear at the crown,arch springing and invert.

Dual fractal features of the surface roughness of natural rock joints

SUN Shengyue1,LI Yingchun1,TANG Chun?an1,LI Bo2
 2019, 38 (12): 2502-2511 doi: 10.13722/j.cnki.jrme.2019.0542
Full Text: [PDF 557 KB] (143)
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To characterize the morphological properties of natural rock joints and to quantify waviness and unevenness of rock joints,the cut-off grid size and cut-off wave vector were established as the critical parameters for two-order roughness decomposition through the classic triangular-prism method(TPM),and the fractal dimensions and root mean squares of the two-order roughness were respectively calculated through the power spectrum density method(PSD). The scale dependence of the fractal parameters of the two-order roughness was investigated for three large-scale natural granite joints. It is found that TPM is universally applicable for separating waviness and unevenness of the joint surface at various sizes,whereas the cut-off grid size and cut-off wave vector depend on the range of the joint surface size. Waviness and unevenness of the rock joint with a size varying from 100 mm×100 mm to 1 000 mm×1 000 mm own individual fractal dimension. The fractal dimensions of two-order roughness exhibit random scale effect. It is also shown that,as the joint size increases,the root mean square of the waviness increases,whereas the root mean square of the unevenness which is obviously smaller than that of the waviness varies smoothly. Accurate characterization of the two-order roughness facilitates in-depth understanding of the shear slip of geological discontinuities,by which the early warning of geological disasters such as slip bursts can be predicted.

Damage analysis and deformation early warning of surrounding rock mass during top arch excavation of underground powerhouse of#br# Shuangjiangkou hydropower station

QIAN Bo1,XU Nuwen1,XIAO Peiwei1,2,ZHAO Tieshuan3,DONG Linlu1
 2019, 38 (12): 2512-2524 doi: 10.13722/j.cnki.jrme.2019.0476
Full Text: [PDF 2593 KB] (82)
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A three-dimensional spatial microseismic monitoring system of the underground powerhouse at the left bank of Shuangjiangkou hydropower station was constructed to pick up the surrounding rock microseismic signals during the excavation period,and the surrounding rock damage area was determined according to the microseismic activity characteristics. The relationship between spatio-temporal evolution characteristics and construction dynamic response of microseismic activity was analyzed based on conventional monitoring results and on-site exploration,and the evolution law of the fractal dimension of the surrounding rock from progressive damage to macroscopical deformation was revealed adopting the fractal-rock mechanics theory. The results show that the microseismic activity is closely related to the construction conditions and geological conditions. The microseismic event of the downstream side of 0–57 m–0–43 m in the installation interval is controlled by the blasting excavation strength and the giant rock mass fissure. The damage of surrounding rock mass exhibits non-shear rupture characteristics,and the microseismic signal shows low-frequency characteristics when the rupture scale increases. It is also revealed that the steep drop of the fractal dimension is the precursor signal of macroscopical deformation of surrounding rock mass. The research results can provide reference for the analysis of surrounding rock damage and deformation warning in underground powerhouse excavation.

Numerical analysis of the bearing capacity of floating energy piles during the full#br# process of thermal-mechanical coupling

JIANG Gang1,LI Renfei1,WANG Hao1,CHEN Gen1,2,LU Hongwei3,SHAO Dong1
 2019, 38 (12): 2525-2534 doi: 10.13722/j.cnki.jrme.2019.0273
Full Text: [PDF 583 KB] (52)
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The energy pile,integrating the heat exchange tubes of the ground source heat pump and the pile foundation of the building,has better heat transfer performance with a larger length of the energy pile,but at the same time,the coupled thermal-mechanical behaviors become more complicated and are paid little attention to. Taking a 40 m long floating energy pile of the Kunshan energy pile project as an example,a simplified thermo-mechanical coupling numerical model was established,and the bearing performance of the pile and the displacement behavior of the pile top during the whole process of load-temperature coupling were studied. The results indicate that the load transfer characteristics such as the pile axial force,shaft resistance and settlement of the floating energy pile are influenced obviously by temperature change when the load is lower than 50% of the ultimate load Pu. When the load is equal to 25% Pu and 50% Pu,the maximum change of the axial force of the floating energy pile respectively increase to 3.1 times and 1.6 times,and the settlement change range of the pile is over 66% and 25% respectively. When the load level of the pile is higher than 75% Pu,the pile load will have dominant effect on load transfer characteristics of the floating energy pile,and the changes of the axial force and shaft resistance of the energy pile will gradually decrease induced by load cooling/heating effect. Due to that the settlement of the energy pile will increase obviously under cooling,it is not suitable for the floating energy to continue to play a role. It is suggested that the load should be controlled less than 75%Pu while considering a engineering pile as an energy pile and that the thermo-mechanical effect on bearing performance of the energy pile should be concerned.

Influence of temperature effect on shear strength and particle breaking evolution characteristics of coral reef sand

HE Shaoheng1,XIA Tangdai1,LI Lingling1,DING Zhi2,SHAN Huafeng3
 2019, 38 (12): 2535-2549 doi: 10.13722/j.cnki.jrme.2019.0170
Full Text: [PDF 908 KB] (59)
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In the construction of many high-temperature infrastructure projects such as submarine oil and gas pipelines in South China Sea,it is necessary to master the effect of temperature on the mechanical properties of coral reef sand on which these projects are seated. The drained triaxial shear tests of coral reef sand from South China Sea were carried out under different temperatures,and the effects of high temperature on shear strength,particle breakage,friction angle and critical state of coral reef sand were studied in depth by comparing with the test results of quartz sand. It is shown that the effects of temperature on the mechanical behaviors of quartz sand and coral reef sand are quite different. Increasing temperature causes pore water discharge of quartz sand,increases the effective contact of soil particles and consequently increases the shear strength and dilatancy of quartz sand. However,increasing temperature results in a significant decrease in both shear strength and dilatancy due to particle breakage and rearrangement of coral reef sand. There exists a temperature threshold value. When the temperature is higher than the threshold value,increasing temperature causes the coral reef sand particles to break and the shear strength to decrease significantly. With increasing the temperature,the relative particle breakage index of coral reef sand increases,and the critical state line in the p?-q plane rotates towards p?-axis. The peak and critical friction angles of coral reef sand have a corresponding negative correlation function relationship with the relative particle breakage index of coral reef sand.

Test study on deformation and failure mechanisms of utility tunnels obliquely crossing ground fissures

HU Zhiping1,2,ZHANG Dan1,ZHANG Yaguo1,2,WANG Shaoqing1,LI Fangtao1
 2019, 38 (12): 2550-2560 doi: 10.13722/j.cnki.jrme.2019.0308
Full Text: [PDF 530 KB] (66)
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Taking the ground fissure sites in Xi?an area as the research background,indoor physical model tests of an underground utility tunnel crossing ground fissures at an angle of 45°were performed with a geometrical reduction ratio of 1:15. The pressure of the peripheral soil and the surface strain,convergence displacement and macroscopic failure of the utility tunnel under the relative movement between the hanging and foot walls were analyzed,and the deformation and failure mode of the utility tunnel were introduced. The results indicate that the longitudinal contact pressure between the soil and the top face of the structure significantly increases in the hanging wall while decreases in the foot wall as the relative movement develops,and that the lateral contact pressure in the intersectant range between the ground fissure and the structural axis is relative larger. The longitudinal and ring cracks in the structure surface distribute respectively in the ranges of 2.9D–5.1D(D = 0.277 m) and 0.9D in the foot wall. The deformation of the utility tunnel is asymmetric and the deformation in the hanging wall is higher than that in the foot wall. The structure is in a complex stress state of torsion, bend and shear,and hence,can be considered as a thin-walled member. The research can provide some references for the structural design and the formulation prevention of underground utility tunnels in Xi?an city.

Intrusion behaviors of highly compacted bentonite into host-rock#br# fractures in a HLW disposal repository

HUANG Yiyi1,2,CHEN Bao1,2
 2019, 38 (12): 2561-2569 doi: 10.13722/j.cnki.jrme.2019.0198
Full Text: [PDF 422 KB] (28)
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The intrusion-flushing behaviour of compacted bentonite buffer/backfill materials may produce uncertainties to the long-term security of HLW disposal repositories. In this paper,concentrating on the issue of bentonite intrusion,the intrusion behaviour of highly compacted Gaomiaozi(GMZ) bentonite into fractures was investigated using an intrusion instrument,and five groups of tests with different parametric combinations of the fracture aperture(df) and the initial dry density( )were performed. The evolution curves of the intrusion distance and the swelling pressure were obtained,the mass loss of the core bentonite was analysed,and the influence of df and on the intrusion behaviour of bentonite was discussed. The results show that both df and   have great influence on the overall intrusion velocity,the total intrusion amount and the state variation of the core bentonite. The values of the slope of the linear portion of the intrusion distance evolution curve,A,reflecting the overall intrusion velocity,in the cases of the maximum df and the maximum are respectively 2.5 times and 2.1 times as big as those in the cases of the minimum df and the minimum ,and correspondingly,the total intrusion amount values are 3.1 times and 2.8 times respectively. The swelling pressure drop percentages corresponding to the maximum df and the maximum   are respectively 53.1% and 48.6%,which are much higher than 3.6% and 17.6% corresponding to the minimum df and the minimum . It can be concluded that a larger df or a larger will produce a stronger outflow of bentonite mass.

Field test and numerical analysis of a helical steel pile under vertical compression loads considering installation effects

SHAO Kang1,SU Qian1,2,LIU Kaiwen1,2,LI Ting1,ZHOU Heng1
 2019, 38 (12): 2570-2581 doi: 10.13722/j.cnki.jrme.2019.0581
Full Text: [PDF 528 KB] (42)
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An in-situ vertical compression load test of a helical steel pile was conducted in silty sand and sand in order to study the bearing characteristics of helical piles in sandy soils under vertical compression loads. The difference of the existing methods for determining the ultimate bearing capacity of the helical pile tested was discussed. A finite element model of the helical pile under a vertical load considering installing effects was established based on soil layer parameters obtained from field cone penetration tests,and comparison of the pile load-displacement curves between the calculation and measuring results was performed. Based on the numerical simulation,the distributions of the axial force and shaft friction force of the pile along the depth under different load levels were explored,and the magnitudes of the shaft and end resistances and their ratio were investigated. The results show that the ultimate bearing capacity calculated by lgP-s method is larger than those obtained by Livneh & E1 Naggar and modified Davisson approaches,which indicates the later two methods over-conservative and that the simulation P-s curve considering installation effects gives better agreement with field measurement than that without considering installation effects. Under vertical compressive loading,the shaft resistance of the pile and the end resistance of middle-upper plates of the pile take effect almost simultaneously,and with increasing the vertical load,the end resistance provided by lower plates comes into play and increases gradually up to a peak value about 71% of the ultimate load with a displacement of the pile head exceeding about 4% of the diameter of plates.

Field experiment on blasting vibration effect of underpass gas pipelines

ZHU Bin1,JIANG Nan1,JIA Yongsheng2,3,ZHOU Chuanbo1,LUO Xuedong1,WU Tingyao1
 2019, 38 (12): 2582-2592 doi: 10.13722/j.cnki.jrme.2019.0183
Full Text: [PDF 530 KB] (39)
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 2019, 38 (12): 2599-2560
Full Text: [PDF 338 KB] (78)
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