查看更多>>摘要：Lunar in-situ resource utilization (ISRU) has been put on the agenda by many countries.Due to the special material nature and low gravity environment,the lunar regolith demonstrates significantly different behavior from terrestrial geomaterials.However,the systematic understanding of its geotechnical behav-ior is now seriously restricted by the scarcity of lunar regolith and the difficulty in simulating lunar grav-ity.A new lunar regolith simulant,termed as China University of Mining and Technology Number One(CUMT-1),has been developed to recover properties of the lunar regolith and simulate the lunar gravity by adopting the recently advanced geotechnical magnetic-similitude-gravity model testing (GMMT)method.The CUMT-1 simulant was prepared by reproducing the in-situ formation and fragmentation of the lunar matrix,which plays a key role in the irregular particle morphology.The mineralogical com-positions,particle morphology and gradation,specific gravity,bulk density,void ratio,shear strength,and compressibility were determined.After quantifying the magnetization and magnetic-similitude-gravity characteristics,an application of the cone penetration resistance under low gravity was further given.The obtained results are compared to the values known for lunar regolith samples and other simulants,which demonstrates promising characteristics for use in geotechnical engineering-based and scientific-based applications,especially considering the influence of lunar gravity.
查看更多>>摘要：As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO2 through P-wave velocity during CO2 sequestration in coal.However,the effects of CO2 on the coal P-wave velocity under triaxial stress are not clearly discerned.In the present study,different bound-ary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO2.Experiments with helium indicated that the pore pressure primarily affected the P-wave velocity by altering the effective stress.Experiments with CH4 and CO2 indicated that matrix swelling induced-cleats porosity decline significantly promoted P-wave velocity.Moreover,CO2 caused a wider scale and severe weakening of coal matrix than CH4,thereby significantly decreasing the P-wave velocity,and the decline in P-wave velocity increases with vitrinite content.Furthermore,experiments under different boundary conditions showed that with the boundary condition having more constraints,the decrement of pore pressure on P-wave velocity is more weaken,whereas the improvement of matrix swelling on P-wave velocity is more evident.This study contributes to understanding the mechanism of effect of CO2 on P-wave velocity under triaxial stress condition and provides guidance for monitoring CO2 sequestration in coal.
查看更多>>摘要：Static cracking agent (SCA) is actively investigated as an alternative to explosive blasting for rock break-age due to its immense expansion property.SCA can eliminate the negative effects of shock,noise and harmful gases encountered in explosive blasting processes.Accurate measurement and deep understand-ing of the expansive properties of SCAs are important in their industrial application.An improved outer pipe method (OPM),termed the upper end surface method (UESM),is proposed in this paper to overcome the shortcomings of the OPM in the expansive pressure measurement of SCAs.Numerical simulation is used to proof the concept and a mathematical model established to relate the internal pressure and the radial strains at different positions in the upper end surface method test equipment.The new equip-ment is calibrated using oil pressure and strain measurements.The calibrated equipment is then used to measure the expansion pressure of SCA at three different water contents to proof its potential.The dif-ferences in the measurements with OPM and UESM at three different moisture contents are less than 4％.The experimental results confirm the accuracy and applicability of the more user friendly and less expensive UESM in the measurement of the expansive pressures of SCAs.
查看更多>>摘要：Sandstone is widely distributed in cold regions and the freeze-thaw deterioration of them has caused many geological engineering disasters.As an important and direct index of frost resistance,the strength loss of sandstones under freeze-thaw actions should be investigated to provide a guidance for the stabil-ity assessment of geological engineering.In this research,the UCS (Uniaxial compressive strength) loss of six typical sandstones with different water contents after 0,20,40 and 60 freeze-thaw cycles was mea-sured in the laboratory.The experimental results indicated that the freeze-thaw damage was more seri-ous in sandstones containing high water contents,and the critical saturations for causing a significant loss of UCS under freeze-thaw were 60％-80％ for these sandstones.Below this critical saturation,the UCS loss of the sandstones was mainly caused by water weakening rather than freeze-thaw damage.Besides,a developed strength prediction model was proposed by combining the exponential decay func-tion and multiple linear regression method.The initial porosity,elastic modulus and tensile strength of fresh sandstones were a good parameter combination to accurately determine the decay constant in this developed model.The main novelty of this model is that it can accurately and easily estimate the UCS loss of sandstones after any freeze-thaw cycle only using the initial parameters of fresh sandstones,but it does not need to perform freeze-thaw and mechanical strength experiments.This study not only provides an accurate prediction model of UCS under freeze-thaw,but also makes a contribution to better under-standing the frost resistance mechanism of sandstones.
查看更多>>摘要：Due to the significant effect of abnormal arrivals on localization accuracy,a novel acoustic emission (AE)source localization method using clustering detection to eliminate abnormal arrivals is proposed in the paper.Firstly,iterative weight estimation is utilized to obtain accurate equation residuals.Secondly,according to the distribution of equation residuals,clustering detection is used to identify and exclude abnormal arrivals.Thirdly,the AE source coordinate is recalculated with remaining normal arrivals.Experimental results of pencil-lead breaks indicate that the proposed method can achieve a better local-ization result with and without abnormal arrivals.The results of simulation tests further demonstrate that the proposed method possesses higher localization accuracy and robustness under different anomaly ratios and scales;even with abnormal arrivals as high as 30％,the proposed localization method still holds a correct detection rate of 91.85％.
查看更多>>摘要：Understanding the mechanism of progressive debonding of bolts is of great significance for underground safety.In this paper,both laboratory experiment and numerical simulation of the pull-out tests were per-formed.The experimental pull-out test specimens were prepared using cement mortar material,and a relationship between the pull-out strength of the bolt and the uniaxial compressive strength (UCS) of cement mortar material specimen was established.The locations of crack developed in the pull-out pro-cess were identified using the acoustic emission (AE) technique.The pull-out test was reproduced using 2D Particle Flow Code (PFC2D) with calibrated parameters.The experimental results show that the axial displacement of the cement mortar material at the peak load during the test was approximately 5 mm for cement-based grout of all strength.In contrast,the peak load of the bolt increased with the UCS of the confining medium.Under peak load,cracks propagated to less than one half of the anchorage length,indi-cating a lag between crack propagation and axial bolt load transmission.The simulation results show that the dilatation between the bolt and the rock induced cracks and extended the force field along the anchorage direction;and,it was identified as the major contributing factor for the pull-out failure of rock bolt.
查看更多>>摘要：Thermogravimetric analysis/differential scanning calorimeter (TGA/DSC) technique along with basic coal characteristics study is carried out for eighty coal samples of Indian coalfields,to determine spontaneous combustion propensity behaviour of coal.TGA study of coal samples indicates that there is an increase in the mass of coal samples in the temperature range 150-350 ℃,which may be due to oxygen adsorption and absorption.The correlation and principal component analysis states that the component of proxi-mate analysis (Mad,VMd,FR,and VR) have an acceptable correlation with the TGA experiments results i.e.,Tgsh and Tgign.Multiple fixed nonlinear regression analysis shows that thermogravimetry (TG) exper-iment results Tgign may be the best index to categorise/classify the coal as per their susceptibility towards spontaneous combustion.The authors proposed four groups of classification as per their propensity towards spontaneous combustion depending upon the moisture (Mad),volatile matter (VMd),and TG ignition temperature from differential thermogravimetric (DTG) curve (Tgign) using hierarchal clustering analysis.The coal samples of different seams from Indian coalfield may be classified into four different clusters,viz.very highly/extremely susceptible (Tgign ＜ 260 ℃),highly susceptible (260 ℃ ≤ Tgign ＜ 290℃),moderately susceptible (290 ℃ ≤ Tgign ≤ 320 ℃),and poorly susceptible (Tgign ＞ 320 ℃).The field observations and TGA/DSC experiment results with the following statistical analysis substantiate a sim-ilar assessment.
查看更多>>摘要：To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tests were conducted for the damaged samples.Besides,coupling modeling technology of finite difference method (FDM)-discrete element method (DEM) was used to carry out the numerical investigation.The results show that after multiple impacts,more white patches appear on the surface,and some microcracks,macro-fractures as well as pulverized grains are found by optical microscopic.The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample.The interaction between grains in the damaged sample becomes intense in the subsequent static loading process,causing a relatively large strain.The volume of the fragments falling off around the loading points becomes larger as impact number increases.As the dynamic damage increases,the absorbed energy of sample during the static loading first decreases and then tends to he stable.Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.
查看更多>>摘要：Ultra-thick steep coal seam mining will inevitably lead to the increase of greater and violent ground sub-sidence and deformation.A subsidence control method by inversely-inclined slicing and upward mining is proposed in this paper.By this method,the sequence of collapse of overlying strata and the direction of propagation of strata movement are changed,the extent of roof-side deformation thereby is lessened,and boundary angle of roof-side subsidence is reduced by 5°-10°.The mechanism of this mining method for control of strata movement has been evidenced by numerical simulation and experiments with similarity materials.A subsidence prediction model based on the variation of mining influence propagation angle can be used to evaluate the surface movement and deformation of the mining method.The application of the method in No.3 Mine in Yaojie mining area has yielded the expected result.
Vladimir S.LitvinenkoMikhail V.DvoynikovVladimir L.Trushko
113-119页
查看更多>>摘要：Currently,construction of facilities in the Arctic is carried out on sand islands,but there are limitations for remote coastal conditions.These restrictions are associated with the lack of quarries with construction sand in the immediate vicinity of the work site,as well as the risk of seasonal flooding of the territories.This article includes conceptual solutions for construction of modular piling in Arctic nearshore condi-tions,upon which drilling rigs and auxiliary equipment can be placed for the purpose of subsequent wild-catting,development and exploratory extended reach drilling wells (with measured depth about 15000 m).During the construction of the modular piling foundations,a mathematical simulation of the thermodynamic condition of the frozen ground was conducted,and the bearing capacity of the foun-dations was assessed.The proposed solutions will solve these problems by constructing modular pile foundations and placing the necessary infrastructure on them,taking into account the distribution of loads during operation in seasonally flooded areas.
NETL
NSTL
万方数据
维普