Heterogeneous information phase space reconstruction and stability prediction of filling body–surrounding rock combination

Traditional research believes that the filling body can effectively control stress concentration while ignoring the problems of unknown stability and the complex and changeable stress distribution of the filling body–surrounding rock combination under high-stress conditions.Current monitoring data processing methods cannot fully consider the complexity of monitoring objects,the diversity of monitoring methods,and the dynamics of monitoring data.To solve this problem,this paper proposes a phase space reconstruction and stability prediction method to process heterogeneous information of backfill–surrounding rock combinations.The three-dimensional monitoring system of a large-area filling body–surrounding rock combination in Longshou Mine was constructed by using drilling stress,multipoint displacement meter,and inclinometer.Varied information,such as the stress and displacement of the filling body–surrounding rock combination,was continuously obtained.Combined with the average mutual information method and the false nearest neighbor point method,the phase space of the heterogeneous information of the filling body–surrounding rock combination was then constructed.In this paper,the distance between the phase point and its nearest point was used as the index evaluation distance to evaluate the stability of the filling body–surrounding rock combination.The evaluated distances(ED)revealed a high sensitivity to the stability of the filling body–surrounding rock combination.The new method was then applied to calculate the time series of historically ED for 12 measuring points located at Longshou Mine.The moments of mutation in these time series were at least 3 months ahead of the roadway return dates.In the ED prediction experiments,the autoregressive integrated moving average model showed a higher prediction accuracy than the deep learning models(long short-term memory and Transformer).Furthermore,the root-mean-square error distribution of the prediction results peaked at 0.26,thus outperforming the no-prediction method in 70%of the cases.

Effects of water intrusion and loading rate on mechanical properties of and crack propagation in coal–rock combinations

Tackling the problems of underground water storage in collieries in arid regions requires knowledge of the effect of water intrusion and loading rate on the mechanical properties of and crack development in coal–rock combinations. Fifty-four coal–rock combinations were prepared and split equally into groups containing different moisture contents(dry, natural moisture and saturated) to conduct acoustic emission testing under uniaxial compression with loading rates ranging from 0.1 mm/min to 0.6 mm/min. The results show that the peak stress and strength-softening modulus, elastic modulus, strain-softening modulus, and post-peak modulus partly decrease with increasing moisture content and loading rate. In contrast, peak strain increases with increasing moisture content and fluctuates with rising loading rate. More significantly, the relationship between stiffness and stress, combined with accumulated counts of acoustic emission, can be used to precisely predict all phases of crack propagation. This is helpful in studying the impact of moisture content and loading rate on crack propagation and accurately calculating mechanical properties. We also determined that the stress thresholds of crack closure, crack initiation, and crack damage do not vary with changes of moisture content and loading rate, constituting 15.22%, 32.20%, and 80.98% of peak stress, respectively. These outcomes assist in developing approaches to water storage in coal mines, determining the necessary width of waterproof coal–rock pillars, and methods of supporting water-enriched roadways, while also advances understanding the mechanical properties of coal–rock combinations and laws of crack propagation.

Mapping of oil-source faults in reservoire-cap rock combinations without a source rock

Oil and gas exploration near faults in shallow strata is investigated in this study based on an analysis of oil-source faults in reservoire-cap rock combinations without a source rock.The oil-source faults were mapped by superimposition of the distribution area of oil-source faults and the leakage area of cap rocks.This method is applied to the mapping of oil-source faults for two sets of reservoire-cap rock combinations without a source rock in the Banqiao area of the Qikou Sag in the Bohai Bay Basin,eastern China.Combination B is formed by a mudstone cap rock of the middle sub-member of the 1st member of the Shahejie Formation(E3s1 M)with its underlying reservoir,while Combination C is formed by a mudstone cap rock of the 2nd member of the Dongying Formation(E_(3)d_(2))with its underlying reservoir.The results show that the oil-source faults of Combination B are relatively better developed and mainly occur in the northeast and southeast,while those of Combination C are not as well developed and are only distributed at the southeastern edge of the study area with a small proportion in the north.These results are consistent with the fact that oil and gas are mainly distributed near oil-source faults,proving the method proposed is workable in determining the oil-source faults in reservoire-cap rock combinations without a source rock.

Mechanical performance of rock bolts under combined load conditions

Rock bolts are subjected to different loading conditions along their lengths such as axial,bending,and/or shear forces,which can cause failure at lower loads than those considered for design purposes.The common existing methodologies do not consider the actual loading of the rock bolts and assume it is only pure axial or pure shear.This study was conducted to investigate the un-grouted rock bolt performance under combined load conditions.Two loading regimes were evaluated:the effect of initial shear displacement on axial load capacity and displacement,and the effect of axial displacement on the shear load capacity.The first regime was also conducted for shear with a gap,when there is a spacing between the shear interfaces.The results of this study showed that the rock bolt can resist higher axial loads than shear under pure or combined load conditions.Under combined load conditions,the rock bolt capacity decreased significantly for both regimes.However,when applying the shear load with a gap,the rock bolt load capacity was not affected significantly.Also,the total bar deformation was improved for shear and axial.The findings of this study show the need to improve the rock bolt design considering the complex loading conditions in situ with/without a gap.

Experimental Study on Dynamic Mechanical Properties of Sprayed Concrete-Surrounding Rock Combined Body

To investigate the dynamic response problem of the double medium formed by the adherence of sprayed concrete and surrounding rock in the tunnel,a split Hopkinson pressure bar of 75 mm in diameter was adopted at the ages of 3,7 and 10 d.Experimental results showed that dynamic compressive strength and dynamic increase factors(DIF)of the combined bodies increase with the strain rate.With the growth of strain rate,the critical strain of the combined bodies first increases,then deceases.Furthermore,the combined bodies of 3 d reveal the plastic property and brittle property for 7 d and 10 d when the strain rate is over 80/s.The failure characteristic of the sprayed concrete changes from tearing strain damage to crushing damage as the growth of strain rate,and the failure characteristic of rock presents the tensile failure mode as demonstrated by the scanning electron microscope(SEM).

Failure behavior of a rock-coal-rock combined body with a weak coal interlayer

Using an MTS 815 testing machine,the deformation and failure behavior of a rock-coal-rock combined body containing a weak coal interlayer has been investigated and described in this paper.Uniaxial loading leads to the appearance of mixed cracks in the coal body which induce instability and lead to bursts in coal.If the mixed crack propagates at a sufficiently high speed to carry enough energy to damage the roof rock,then coal and rock bursts may occur-this is the main mechanism whereby coal bumps or coal and rock bursts occur after excavation unloading.With increasing confining pressure,the failure strength of a rock-coal-rock combined body gradually increases,and the failure mechanism of the coal interlayer also changes,from mixed crack damage under low confining pressures,to parallel crack damage under medium confining pressures,and finally to single shear crack damage or integral mixed section damage under high confining pressures.In general,it is shown that a weak coal interlayer changes the form of overall coal damage in a rock-coal-rock combined body and reduces the overall stability of a coal body.Therefore,the whole failure behavior of a rock-coal-rock combined body in large cutting height working faces is controlled by these mechanisms.

Determination of combined effect of ampli- fication and attenuation of soft rock site us- ing digital seismic data

In the paper, for the application of stochastic simulation of ground motion, we put forward a method to determine ″the combined effect of amplification and attenuation″ (combined effect for short) of soft rock site by using digital seismic data of moderate and small earthquakes. Our approach aims at solving the problem of the combined effect of soft rock site, which is difficult to determine in most regions of China because fewer measures were done for S-wave velocity structure. The combined effect of soft rock site can be determined by using the approach recom- mended by us. An example is given to discuss the practical application of the method.

Combined blasting for protection of gob-side roadway with thick and hard roof

The deformation control of surrounding rock in gobside roadway with thick and hard roof poses a significant challenge to the safety and efficiency of coal mining.To address this issue,a novel approach combining directional and non-directional blasting techniques,known as combined blasting,was proposed.This study focuses on the experimental investigation of the proposed method in the 122108 working face in Caojiatan Coal Mine as the engineering background.The initial phase of the study involves physical model experiments to reveal the underlying mechanisms of combined blasting for protecting gob-side roadway with thick and hard roof.The results demonstrate that this approach effectively accelerates the collapse of thick and hard roofs,enhances the fragmentation and expansion coefficient of gangue,facilitates the filling of the goaf with gangue,and provides support to the overlying strata,thus reducing the subsidence of the overlying strata above the goaf.Additionally,the method involves cutting the main roof into shorter beams to decrease the stress and disrupt stress transmission pathways.Subsequent numerical simulations were conducted to corroborate the findings of the physical model experiments,thus validating the accuracy of the experimental results.Furthermore,field engineering experiments were performed,affirming the efficacy of the combined blasting method in mitigating the deformation of surrounding rock and achieving the desired protection of the gob-side roadway.

Surrounding Rock Control Technology of Strong Dynamic Pressure Roadway in Hudi Coal Industry

Aiming at the problems of large deformation and difficult maintenance of deep soft rock roadway under the influence of high ground stress and strong dynamic pressure, taking the surrounding rock control of 1105 lane in Hudi Coal Industry as an example, the deformation characteristics and surrounding rock control measures of deep soft rock roadway are analyzed and discussed by means of geological data analysis, roadway deformation monitoring, rock crack drilling and field test. The results show that the main causes of roadway deformation are high ground stress, synclinal tectonic stress, advance mining stress, roadway penetration and surrounding rock fissure development. Based on the deformation characteristics and mechanism of lane 1105, the supporting countermeasures of “roof synergic support, layered grouting, anchor cable beam support, closed hardening of roadway surface” are proposed, which can provide reference for the control of deep roadway surrounding rock under similar conditions.

Rock burst mechanism analysis in an advanced segment of gob-side entry under different dip angles of the seam and prevention technology

In order to investigate the frequent occurrences of rock burst in gob-side entry during the mining process of the mining zone No. 7, the mechanical model of main roof of fully-mechanized caving mining before breaking was established by the Winkler foundation beam theory, and the stress evolution law of surrounding rock with different dip angles of the seam during the mining process was analyzed by using FLAC3 D. The results show that: with the dip angle changing from 45° to 0°, the solid-coal side of gobside entry begins to form an L-shaped stress concentration zone at a dip angle of 30°, and the stress concentration degree goes to higher and higher levels. However, the stress concentration degree of the coalpillar side goes to lower and lower levels; the influence range and peak stress of the abutment at the lateral strata of adjacent gob increase with dip angle decreasing and reach a maximum value at a dip angle of 0°, but the tailgate is not affected; the abutment pressure superposition of two adjacent gobs leads to stress concentration further enhancing in both sides of gob-side entry. With the influence of strong mining disturbance, rock burst is easily induced by dynamic and static combined load in the advanced segment of gob-side entry. To achieve stability control similar to that in the roadway, the key control strategy is to reinforce surrounding rock and unload both sides. Accordingly, the large-diameter drilling and high-pressure water injection combined unloading and reinforced support cooperative control technology was proposed and applied in field test. The results of Electromagnetic Emission(EME) and field observation showed that unloading and surrounding rock control effect was obvious.

Mechanism of rock burst caused by fracture of key strata during irregular working face mining and its prevention methods

To study the occurrence mechanism of rock burst during mining the irregular working face,the study took irregular panel 7447 near fault tectonic as an engineering background.The spatial fracture characteristic of overlying strata was analyzed by Winkler elastic foundation beam theory.Furthermore,the influence law of panel width to suspended width and limit breaking span of key strata were also analyzed by thin plate theory.Through micro-seismic monitoring,theoretical analysis,numerical simulation and working resistance of support of field measurement,this study investigated the fracture characteristic of overlying strata and mechanism of rock burst in irregular working face.The results show that the fracture characteristic of overlying strata shows a spatial trapezoid structure,with the main roof being as an undersurface.The fracture form changes from vertical‘‘O-X"type to transverse‘‘O-X"type with the increase of trapezoidal height.From the narrow mining face to the wide mining face,the suspended width of key strata is greater than its limit breaking width,and a strong dynamic load is produced by the fracture of key strata.The numerical simulation and micro-seismic monitoring results show that the initial fracture position of key strata is close to tailgate 7447.Also there is a high static load caused by fault tectonic.The dynamic and static combined load induce rock burst.Accordingly,a cooperative control technology was proposed,which can weaken dynamic load by hard roof directional hydraulic fracture and enhance surrounding rock by supporting system.

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Influence of dynamic pressure on deep underground soft rock roadway support and its application

Due to high ground stress and mining disturbance, the deformation and failure of deep soft rock roadway is serious, and invalidation of the anchor net-anchor cable supporting structure occurs. The failure characteristics of roadways revealed with the help of the ground pressure monitoring. Theoretical analysis was adopted to analyze the influence of mining disturbance on stress distribution in surrounding rock,and the change of stress was also calculated. Considering the change of stress in surrounding rock of bottom extraction roadway, the displacement, plastic zone and distribution law of principal stress difference under different support schemes were studied by means of FLAC3D. The supporting scheme of U-shaped steel was proposed for bottom extraction roadway that underwent mining disturbance. We carried out a similarity model test to verify the effect of support in dynamic pressure. Monitoring results demonstrated the change rules of deformation and stress of surrounding rock in different supporting schemes. The supporting scheme of U-shaped steel had an effective control on deformation of surrounding rock. The scheme was successfully applied in underground engineering practice, and achieved good technical and economic benefits.

Establishing the need to model the actual state of stress along rock bolts

Proper design of rock bolt support in underground mines is critical to avoid incidents, accidents and loss of production. The traditional design approach only considers the axial(tensile) capacity and this is clearly not the situation in situ, where a rock bolt is subjected to both axial and shear/bending loads which determines its overall performance and failure behaviour. To demonstrate and analyse the shear displacement in bedded roof, scaled physical models of underground excavation were created. From the models it was found that the shear displacement between the layers depends on the vertical roof deformation and thickness of beds. To analyse the effect of combined loading on rock bolt design for suspension and beam building models, analytical methods were used to calculate the required spacing of rock bolt for a given safety factor. Numerical models were then created using Rocscience RS2 software to establish the stresses on the rock bolt. The results show a significant reduction in safety factor for suspension as demonstrated in an example(reduced from 3.5 to 2.0) and beam building(2.0 to 1.36) when the rock bolt capacities are calculated considering the effect of combined loading as opposed to just the axial or shear loads.

Experimental study of a new multifunctional device for rock fragmentation

A new multifunctional testing device for rock fragmentation was introduced, which can conduct many experiments such as single cutting under static load, crushing under impact load, thrusting under static load and cutting-impact test under the dynamic and static load. The results of granite and concrete抯 experiments with polycrystalline diamond compact (PDC) flat cutters and carbide alloy cutters under different loadings show that the device has good performance, and the characteristics of broken rock under the combined loads are similar to that under the single static pressure or impact crushing the rock, and the combined loads can increase the effect of rock fragmentation obviously. The experimental methods and effects have the important meaning for studying new drill-ing tool on hard rock fragmentation.

针药结合对糖尿病胃轻瘫大鼠胃窦RhoA/ROCK/MLC信号通路的影响

目的:观察针刺结合益气健脾中药复方对糖尿病胃轻瘫(DGP)大鼠胃肠动力的影响,探讨其可能的作用机制。方法:SD大鼠随机分为空白组、模型组、针刺组、中药组、针药组和西药组,除空白组外采用链脲佐菌素(STZ)尾静脉注射及高糖高脂不规则喂养法建立糖尿病胃轻瘫模型。成模后针刺组每日给予三阴交、足三里穴针刺30 min治疗,中药组每日给予益气健脾中药复方5 g/kg灌胃,针药组先给予益气健脾中药复方5 g/kg灌胃再行针刺(操作同针刺组),西药组每日给予多潘立酮3.15×10^(-3) g/kg灌胃,模型组和空白组每日给予生理盐水10 mL/kg灌胃1次,所有治疗持续4周。治疗过程中记录大鼠一般情况,4周后记录血糖、体质量,酚红灌胃法检测胃排空率及小肠推进率,免疫组化法测定胃窦组织中Ras同源物基因组成员A(RhoA)、Rho蛋白相关卷曲螺旋激酶2(ROCK2)阳性表达,Western blot法测定胃窦组织中磷酸化肌球蛋白磷酸酶靶亚单位1(p-MYPT1)、磷酸化肌球蛋白轻链(p-MLC)蛋白的表达。结果:与空白组比较,模型组大鼠一般情况较差,胃排空率、小肠推进率和RhoA、ROCK2蛋白表达显著降低(P<0.01);与模型组比较,各治疗组大鼠一般情况明显好转,胃排空率、小肠推进率和RhoA、ROCK2、p-MYPT1、p-MLC蛋白表达水平显著升高(P<0.05或P<0.01),针药结合组改善最明显。结论:针刺和中药均可有效促进胃排空,增加小肠推进率,改善胃肠动力,其作用机制可能与上调RhoA/ROCK/MLC信号通路有关,且针药结合疗效更显著。

Mechanical mechanism and support design analysis on bolt-beam-net support in soft rock roadway in Qigou Coal Mine

The deformation and failure mechanical mechanism in soft rock roadway is related to the stability of supported tunnels, which is important to coal mine production and construction. By physical mechanics experiments and X-ray diffraction （XRD） tests, the engineering mechanical properties of soft rock, as well as main mineral composition of the surrounding soft rock of Qigou Coal Mine, were obtained. Based on analysis results, a method using bolt-beam-net combination to support was put forward. Mechanical analysis of the support form was done by using the calculation software FLAC3D. Results show that clay minerals of this mine are kaolinite and illite mixed layer, of which the water absorption is relatively obvious and presented mudding characteristic after absorbing water, with the plasticity index of 0.35, with small expansibility, which is weakly consolidated colloid with strong connected force in unit cell. The rock blocks have the characteristics of moisture absorption softening, and the deformation mechanical mechanism of which is with the coexistence of molecular expansive mechanism, colloid expansive mechanism, and weak layer trend type. The calculation results show that the bolt-beam-net support structure makes the bolt, beam, and roof deform compatibly. The beams make the force in the bolt relatively homogeneous, which restricts the displacement of the tunnel roof as well. Finally, using in situ monitoring, the numerical results were verified.

重复冲击下砂岩的动态响应试验研究

高速动能水击压裂可借助聚能水锤效应实现强动载泄入性液压冲击,具有高峰值压力、高加载速率、重复多次渐进扩缝等优势,其中聚能流体贯入性冲击下岩石损伤-破裂的演化机制是该技术优化设计的核心问题。为此,采用岩石动态冲击损伤模拟试验装置,开展高速动能水击压裂破岩试验,分析不同加载速率、冲击次数、冲击组合等对岩石破裂形态的影响规律。结果表明:单次高速动能水击破岩中,随着加载速率的提高,岩石破坏依次呈现出近孔眼破碎损伤(8.5 MPa/ms)、微裂缝聚并串联成宏观裂纹(13.4 MPa/ms)、流体楔入形成脆性崩裂裂缝(15.5 MPa/ms)三种模式;在小峰值压力、低加载速率重复冲击下,岩石损伤破坏呈现近孔眼损伤(1~2次)-裂缝起裂扩展(3~5次)-应力挤压破碎(6~10次)三个阶段,随着冲击次数的增加,孔眼周围损伤加剧,形成3~40 mm(贯穿岩样)不等长的裂缝;“先低后高”组合加载速率冲击方式下,前期重复低速率冲击可在孔眼周围形成微裂纹损伤而又不会产生破碎压实,随后借助单次高加载速率聚能冲击,实现大体积高压流体在微裂纹内的快速楔入,激发多条径向深穿透裂缝,同时该组合冲击方法还可实现主裂缝两侧基质扩容增渗和相交分支缝网,实现改造效果的最大化。

高压水射流辅助锥形PDC齿破碎花岗岩试验研究

深部地层岩石硬度高、研磨性强、可钻性差,地质条件复杂、施工难度大,高压水射流辅助钻井可有效延长钻头寿命,提高钻进效率。采用室内试验与理论分析相结合的方法,开展了高压水射流辅助锥形PDC齿破碎花岗岩试验,分析了高压水射流辅助锥形PDC齿和常规PDC齿破碎花岗岩特性,揭示了射流压力、喷射距离、喷嘴直径及喷射角度等因素对锥形PDC齿破岩效果的影响规律。研究结果表明:在高压水射流辅助破岩条件下,锥形PDC齿与常规PDC齿的破岩比能分别降低了17.36%与19.63%;射流压力越大,射流辅助锥形PDC齿破岩效果越好;在研究条件下,喷距范围为5~10 mm可使水射流辅助锥形PDC齿破岩效果最佳;当喷嘴直径为2 mm时,切削力离散系数最小;喷射角度为30°时,锥形PDC齿切削力与破岩比能达到最小值;喷射角度为20°时,切削力离散系数最小,切削力最稳定。研究结果可为适用于深部硬岩钻井的锥形PDC钻头水力结构设计与优化提供理论支撑。