Zhongchang Wang

The Mechanism Study of Cracks Propagation of Different Floor Strata Combinations Under Mining

To obtain the water resistance performance of floor strata under different rock layers and fracture combination, the two cracks’ propagation path under different situations was given by using minimum plastic zone theory according to the change of the fracture factor and the plastic strain of different strata combination cracks under the influence of fault, water pressure and mining. The shortest distance of the rock bridge between the two cracks after bursting in different strata combination was obtained. And the water resistance performance of every strata combination was analyzed. The conclusion was that the water resistance performance of the floor strata under the 3214 combination of soft–soft–hard–hard was the worst. While the 1243 combination of soft rock, hard rock, soft rock, hard rock was the best. The fracture factor combination and the plastic strain of the crack would reach maximum under mining condition. And the crack was mostly easy to destroy. The distance of the rock bridge between the two cracks after bursting was the shortest under the 3214 combination of soft–soft–hard–hard strata. The distance of the rock bridge between the two cracks after bursting was the longest under the 1243 combination of soft rock, hard rock, soft rock, hard rock strata. And the distance of the rock bridge between the two cracks after bursting would be shorten when considering the water pressure inside the crack and fault, which resulted in the decrease of rock water resistance performance.

Analysis of Prediction Model of Failure Depth of Mine Floor Based on Fuzzy Neural Network

To obtain the law of failure depth of mine floor and its influencing factors during coal mining process, a large amount of field measured data of floor failure depth was collected, and five influencing factors were summarized based on the analysis of data and years of field experience. The five main influencing factors were the length of working face, mining depth, mining height, dip angle and floor anti-sabotage ability. Based on fuzzy math membership and membership function, the five factors were preliminarily processed, then the sensitivity ranking was obtained according to the weight of influencing factors, and the prediction model of failure depth of mine floor was established based on the fuzzy neural network. It was shown that the order of the weight of the five factors was the length of working faceu2009>u2009dip angleu2009>u2009floor anti-sabotage abilityu2009>u2009mining depthu2009>u2009mining height. The maximum weight of the length of working face was 0.3678. The accuracy of the model was high and the prediction results were in good agreement with the engineering practice according to verification results. To ensure the maximum economic benefit of mine, some measures and methods through human intervention to reduce the failure depth of floor and ensure mine safety were suggested.

The Analysis of Compression–Shear Infiltration Characteristics of Joint Rock Under Different Load Conditions

To obtain the compression–shear infiltration characteristics of joint rock, the coupled compression–shear infiltration tests of samples were carried out under different loading and boundary conditions. The shear dilatation, permeability and the change laws of hydraulic opening of jointed rockmass were obtained under different normal stiffness and loading conditions. It is shown that the contact area gradually becomes smaller and smaller with the relative sliding of two jointed surfaces. And the contact ratio is down to a minimum value when the main processes of the jointed surface reach the peak shear strength. The remaining main processes is gradually destroyed, the contact ratio of joint surface becomes larger after the main processes reaches the peak strength. The contact ratio tends to be stable until all processes were all destroyed. Due to the influence of the joint surface protrusion, the normal displacement is smaller and then increases with the increase of shear displacement. The less the stiffness of jointed rock mass is, the greater the over water area of the joint surface is, the greater the permeability is, the greater the final stability value of the hydraulic opening degree is. The theoretical basis is provided for the fractured rock mass formed of permeable channels, initiation and outbreak of permeability disaster evolution process.

The Stability Analysis of Lining Structure of Water Diversion Tunnel of Hydropower in Strong Earthquake Area

To obtain dynamic stability of lining structure of water diversion tunnel under the 100xa0years beyond 1% probability earthquake condition, the three-dimensional dynamic analysis for water diversion tunnel of large hydropower station was conducted by the dynamic time history method. The distribution of plastic zone and response characteristics of the stress and the displacement and acceleration of each key position of water diversion tunnel under earthquake was obtained. It is shown that the lining structure of the diversion tunnel was subjected to forced vibration according to the excitation ground vibration. The greater the peak of ground vibration was, the greater the dynamic displacement and tensile and compressive stress of the lining structure was. The tensile and compressive stress of the upper horizontal section at the entrance among the lining of diversion tunnel was the largest. The maximum tensile stress of the lining at the entrance is 1.3xa0MPa. The stress of tunnel lining was asymmetry in the horizontal direction. Each tunnel was close to the side of the other tunnel, the stress value was larger, and the stress value was smaller away from the side of the other tunnel. The farther the plastic zone of the diversion tunnel was from the entrance and exit of the tunnel, the smaller the plastic zone was. The plastic area of the surrounding rock between the eight water diversion tunnels did not occur through. After the earthquake, the plastic zone was through only in the export position of eight diversion tunnels. The local position in the diversion tunnel was damage under the 100xa0years beyond 1% probability earthquake condition, but the whole tunnels were safe and stable.

Measurement of the Strong Pressure Appearance Laws with Hard Roof and Full Mechanized Mining Extra Thick Coal Seam

To master the laws of strong strata behavior of Tashan coal mine under Carboniferous coal mining process, the laws of strong strata behavior in 8107 working face was measured and analyzed. It was shown that the average initial weighting step of 8107 working face was 59.4xa0m. The average periodic weighting step of main roof was 16.2xa0m. The maximum working resistance during periodic weighting was 14,711.1xa0kN. The maximum working resistance during non-periodic weighting was 11,339.9xa0kN. The average dynamic load factor K during periodic weighting was 1.31. The stress of coal column on the side of the goaf could be divided into four zones (stress stabilization zone, stress slow-increasing zone, significant—increasing stress zone, stress reduction zone) along the strike of 8107 working face. There was a peak of lateral support pressure along the trend of 8107 working face. And the peak position was biased to the side of return airway roadway. With the increase of the distance from the down-side of return airway, the pressure peak of the inner coal body along the strike of 8107 the working face increased and the peak position decreased from the coal wall. The peak stress of coal column tended to be close to the up-side of return airway. And the distance from the down-side of return airway for the peak of inner coal was larger than that for the peak of coal pillar. The peak position of abutment pressure of hard roof was in the range of 10–25xa0m in front of 8107 working face under full mechanized mining extra thickness coal seam conditions. The relative stress concentration coefficient of k was 1.3–6.5. The range of 10–25xa0m from the front of the working face to coal wall was stress reduction zone. And the influence range of abutment pressure was about 80xa0m. It was of great significance to the control and practice of the surrounding rock of the stope for the mining of the hard extra-thick coal seam.

The Hazard Analysis of Water Inrush of Mining of Thick Coal Seam Under Reservoir Based on Entropy Weight Evaluation Method

The water inrush of roof induced by mining was related to the height of water flowing fractured zone under large-scale water bodies. Based on the drilling revealed stratum, the thickness of different overlying layers was obtained within the scope of Santaizi reservoir. The height of water flowing fractured zone of different workface on the outside of reservoir under the condition of fully mechanized level mining area was the prediction sample, the generalized analysis of sensitive factors that affected the development of water flowing fractured zone was carried on. The mining depth, dip angle of coal seam, mudstone ratio, compressive strength, mining thickness and the inclined length of the goaf were selected as the influence factors to predict the height of water flowing fractured zone. The height of water flowing fractured zone of unmined working face within the scope of Santaizi reservoir was obtained by objective entropy method. The index weight value of each influence factor was determined. The thickness of the different overlying rock layers above water flowing fractured zone was obtained. And the safety evaluation of water-inrush of unmined working face within the scope of Santaizi reservoir was studied. The important parameter and technical support were provided for the rational design and mining of the working faces under the reservoir.

Analysis of Pressure Relief Effect on the Protective Layer of Hard Roof and Extra-Thickness Coal Seam Mining

The roof of Tashan coal mine was hard and difficult to fall. In the process of fully mechanized coal caving in the Carboniferous extra-thick coal seam, the strong pressure and rock burst appeared in the working face. To obtain the pressure relief effect of the exploitation of Shan 4# protective seam in Tashan coal mine, The stress distribution and displacement variation of the roof and floor of Shan 4# protective layer were obtained by numerical simulation. And by mine pressure observation in the 8107 working face of the un-mining protective seam and in the 8108 working face of mining protective layer, the pressure relief effect of mining Shan 4# protective layer was analyzed. It was shown that the lateral of the open-off cut and the rock mass in front of the working face produced stress concentration when 3–5# coal was mined separately. The stress concentration coefficient of k was 3. The liberated layer was in the floor relief area from the open-off cut after the upper protective layer being mined owing to internal misaligned arrangement of the liberated layer when the protective layer and the liberated layer were mined. The stress concentration of the lateral of open-off cut and working face of the liberated layer was greatly reduced, and the stress concentration coefficient was about 1.5. The middle of the goaf would be re-compacted with the advance of the working face. The maximum principal stress of the liberated layer was W type distribution. The expansion deformation of 3–5# coal was M type distribution. The working resistance of the 8107 working face was mainly distributed in 8000–12,000xa0kN. The working resistance of the 8108 working face was mainly distributed in 4000–10,000xa0kN. The vertical stress of the roof of the 3–5# coal was decreased by about 30% after mining the protective layer. The mining of the protective seam effectively reduced the pressure strength of the roof of the fully mechanized coal seam. The reference was provided for the rational layout of coal seam safe mining with impact tendencies.

Research on High Strength and Pre-stressed Coupling Support Technology in Deep Extremely Soft Rock Roadway

The roof and floor of transportation roadway of S2S2 working face of Xiaokang coal mine were oil shale and siltstone. The content of clay mineral in the surrounding rock was about 60–80%, which was easy to softening with water and weathering. The deformation of primary archy support roadway was serious and the repair rate was high. To control effectively the deformation of extremely soft rock roadway of Xiaokang coal mine, A combined support system of circular full closed sectionu2009+u2009high strength and pre-stress anchoru2009+u2009“W” stripu2009+u2009powerful anchor cableu2009+u2009shotcreteu2009+u2009360U yieldable steel supportu2009+u2009back wall filling support was suggested. By combining numerical calculation and field measurement, the convergence and convergence velocity of new circular support roadway were analyzed after excavating completion and compared with the value of primary archy support roadway. The convergence and convergence velocity of new circular support roadway significantly decreased. The deformation of surrounding rock tended to be convergent in a relatively short time. The new supporting technology was a kind of effective control method for the large deformation roadway of deep extremely soft rock. The experience for reference was provided for the support of roadway of other similar mine.

Field Monitoring Analysis of Construction Process of Deep Foundation Pit at Subway Station

Taking the excavation of deep foundation pit of a subway station in Ji’nan city as the background, and the measured data of the deep-horizontal displacement, support axis force and the surface settlement of the retaining pile body during the excavation was analyzed. It was shown that with the increase of excavation depth of the foundation pit, the position of the maximum horizontal displacement of the pile gradually moved downward from the top of the pile, and the pile deformation curve gradually changed from a similar cantilever beam to a “bow shaped” curve, the phenomenon of moving to the outside of the pit occurred at the top of the pile in the end-well of subway station. It is necessary to prevent the first reinforced concrete support and the retaining structure from being broken due to the lateral displacement of the top of the pile. The foundation pit excavation caused the settlement of the surrounding surface. The maximum settlement point was about 15xa0m from the boundary of foundation pit. The maximum surface settlement value was located in the middle of the standard section. The maximum settlement was 18.5xa0mm. The maximum horizontal displacement of ZQT37 measuring point at the standard section was 23.79xa0mm, and the location of maximum horizontal displacement was approximately 17xa0m from the top of the foundation pit. The axial force of the concrete support and the third steel supports at the ZCL20 section of the standard section were the largest. All supports were in safe working condition during excavation of the foundation pit.

Analysis of Deep Foundation Pit Construction Monitoring in a Metro Station in Jinan City

In order to study the deformation law of adjacent building structures, surface settlement, displacement of supporting piles, axial force and variation of water level during different excavation stages of deep excavation construction, the deep foundation pit project in the M1 line of the Jinan Metro was used as the background, and the data from field measurement of excavation and support were analyzed. The results show that the horizontal displacement of the pile presented a pronounced “bow” shape with the excavation of the foundation pit. The maximum horizontal displacement of the pile appeared at one third of the top of the pile, with a maximum of 31.98xa0mm. The maximum value of monitored axial force was 3100xa0kN, which was much less than the control value of 6847xa0kN. The maximum axial force appeared on the second steel support. The axial force of the first reinforced concrete support rapidly increased with the time. It was considered that the initial bearing capacity of the concrete was low, so the axial force of the concrete support was smaller than the steel support. The strength and load-bearing capacity of concrete increased in the later period, which resulted in a rapid increase in axial force. At the same time, during the process of setting up or dismantling the support, the attention should be paid to the axial force change of the adjacent support to prevent the danger caused by the abrupt change of the axial force. The maximum settlement value of the building appeared at the two corners far from the foundation pit, with the value of 4.3xa0mm. When the constructions were 34xa0m away from the deep foundation pit, the impact of dewatering on the building was greater than that of the foundation pit excavation, and he effect of the dewatering on the variational soil texture in this area was different. The maximum angular variation of adjacent constructions was 1/16,050, which was less than the 1/5000 of the minimum angular variation. The foundation pit structure and building were in a safe state, and the layout of the supporting structure was reasonable.