基于空芯包体原位应力测试的巷道差异性变形机制及控制技术研究

为了研究不同方向巷道差异变形的地应力机制,采用空芯包体式应力解除法对彬长矿区北部雅店煤矿变形程度不同的巷道进行了地应力测量,结果显示地应力为σ_(H)>σ_(h)>σ_(V),地应力场以水平应力场为主,最大水平主应力方向为NEE-SWW,受控于华北区域构造应力场,此类型地应力场对巷道顶底板的稳定最为不利,南北巷道与东西巷道差异变形的主要因素为水平地应力不均衡和应力集中。中央大巷及井底车场区域最大主应力在12.30~15.41 MPa,属于中等应力区;ZC1101工作面回风顺槽区域最大主应力约为28.10 MPa,属于高应力区,后期回采期间该区域冲击地压影响将较其他区域更为严峻。南北向巷道变形趋于稳定时间为1~2个月,东西向巷道稳定时间5~10 d。实践表明,锚固注浆、U型钢棚喷浆联合支护、锚索+槽钢和锚杆+钢筋网的补强支护能有效地控制巷道变形。

不同岩石破坏准则下水平井井壁失稳分析

在井壁失稳分析过程中,Mohr-Coulomb准则和Drucker-Prager准则是目前运用较为广泛的岩石破坏准则,但2种岩石破坏准则都存在一定的缺陷,从而造成井壁失稳分析的不准确。为此,在引入考虑中间主应力的Mogi-Coulomb准则的基础上,对比计算了不同岩石破坏准则下水平井的井壁坍塌压力值,同时就地应力对水平井坍塌压力值的影响进行了分析。研究结果表明,MohrCoulomb准则下所计算的坍塌压力值最大,Mogi-Coulomb准则下所计算的坍塌压力值次之且更接近实际,而Drucker-Prager准则下所计算的坍塌压力值最小;地应力机制对当量坍塌密度最大值随相对方位角的变化规律影响较大。

Ground movement mechanism in tectonic stress metal mines with steep structure planes

When mining metal mines with steep structure planes by the caving method,there is a mechanical model in which the horizontal stress on the rock mass is simplified as a column before surface subsidence.The model is used to deduce critical support load and limiting column length for a given horizontal stress and support pressure.Considering the impact of the column effect,a method is proposed to determine the movement of the ground and caving area in a mine.After surface subsidence,the horizontal stress on a surrounding rock mass can be simplified to a cantilever beam mechanical model.Expressions for its bending fracture length are deduced,and a method is given to determine its stability.On this basis,an explanation for the large ground movement and subsidence scope was given.A case study shows that the damage effect of column and cantilever beam is significant for ground movement in metal-ore mine,and an appropriate correction value should be applied when designing for its angle of ground movements.

Control technology and coordination deformation mechanism of rise entry group with high ground stress

Based on engineering practices of Wuyang Coal Mine, we carried out X-ray diffract researches on No. 3 coal; and the rocks of its roof and floor by XRD meter, and simulated the interactive effect of the surrounding rock deformation by FLAC2DS.0 numerical simulation software under the condition of different tunneling method of multimine roadway in parallel. The internal structures of the surrounding rocks of 76 belt roadway were monitored by borehole observation instruments： and then, we analyzed the reason of fhilure and deformation of surrounding rocks of several rise entry, and proposed the technical mea- sures for controlling interactive effect of several rise entry surrounding rock deformation at last. For the thickness seam rise roadway, two conclusions were drawn： one is that the co-deformation among roadway groups mainly reflect on that both shear failure and deformation in coal pillar among roadways have decreased the width of pillar core region and clamping action of coal pillar to roof strata, increased the actual span of roof strata, intensified the flexural failure of roof strata and prized the bed separation of roof deep rock strata. The other conclusion is that the factors controlling the interactive deformation among roadways is obvious when appropriate re-adjustment in construction sequence of the tunneling of multimine parallel roadways because the construction sequence among roadways also has great effects on deformation of the surrounding rock in roadway.

Study on the Recent Tectonic Stress Field in the “Huoshan Seismic Window” Region

The focal mechanisms of 62 moderate-small earthquakes since 1980 in the ＂ Huoshan seismic window＂ region are calculated with the method developed recently by Snoke, combining the use of the first motion of P, SV and SH waves with their amplitude ratios. Based on these abundant focal mechanisms, the mean tectonic stress field in the ＂Huoshan seismic window＂ region is inverted with the average stress tensor method, and the result shows that the ＂Huoshan seismic window＂ region is horizontally compressed in the near EW direction and horizontally dilated in the near NS direction, which is in accord with statistical results of focal mechanism parameters. We estimate the difference （also referred to as consistency parameter 0） between the force axis direction of the focal mechanism solution and the mean stress tensor, then further analyze the variation characteristics of 0 versus time, and the relationship with moderately strong earthquakes in the east China region. The result indicates that 0 in the ＂ Huoshan seismic window＂ region is in good correspondence with moderately strong earthquakes in the East China region. When 0 is lower than the mean value, corresponding moderately strong earthquakes may occur in the East China region.

Study on the Recent Tectonic Stress Field in the Yunnan Region

In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Yunnan region. The results show that most moderate-strong earthquakes occurring in the Yunnan region are of the strike-slip type, amounting to 80% of the total. Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes is almost equivalent in proportion, about 8% each. The tectonic stress field of the Yunnan region is near-horizontal, and the dips of earthquake fault planes are large. There are three main dynamic sources acting on the Yunnan region: one is the NE, NNE and NNW-directed acting force from Myanmar, Laos and Vietnam; the second is the SE-SSE directed force from the Sichuan and Sichuan-Yunnan rhombus block and the third is the NW-NNW directed force from the South China block. These three acting forces have controlled the faulting behavior of the main faults and the characteristics of strong earthquake activity of Yunnan and its adjacent regions.

The Focal Mechanism and Characteristic of Stress Field in the Zipingpu Area before the M_S8.0 Wenchuan Earthquake

Based on seismic wave records of the Chengdu digital seismic network and Zipingpu reservoir digital seismic network from August 16,2004 to May 12,2008 when the Wenchuan MS8.0 earthquake occurred,the parameters of focal mechanisms of 486 earthquakes with magnitude larger than M1.6 in the Zipingpu reservoir area were calculated using amplitude ratio method,meanwhile the temporal-spatial variation characteristics of mechanisms and stress field were analyzed based on these parameters.Results show a low ratio of thrust earthquakes and an increased number of strike-slip earthquakes in the reservoir water area in the period from 2006 to 2008.While in the areas far from the reservoir waterfront,the thrust earthquakes took up a high proportion and the strike-slip ones did not increase.The direction of mean principal compressive stress field was deflected and disturbed differently in each area before the Wenchuan MS8.0 earthquake.

Source Mechanism of the M_S 6.6 Xinyuan-Hejing Earthquake of June 30,2012

In this article,we use the CAP method to invert the focal mechanism of Xinyuan-Hejing M S6. 6 earthquake on June 30,2012. Our result shows that the best double couple solution of the M S6. 6 event is 299°,68° and 164° for strike,dip and rake angles respectively. The other nodal plane is 35°,75° and 23°. The azimuth and dip angle of the P-axis are 166°and 5°,those of the T-axis are 258° and 26°. The moment magnitude is 6. 3. The estimated focal depth is about 21 km. The predominant rupture direction of this seismic sequence is NWW. The dip angles are between 60° and 90°. The rake angles are in the majority of ± 180°± 30°. The predominant strike of the azimuthal angle of the P-axis is near NS and T-axis is near EW. Preliminary analysis indicates that nodal plane I is the seismogenic fault,which is a NWW-trending,nearly upright left-lateral strike-slip fault.The displacement property,the principal compressive stress of this M S6. 6 earthquake and the P-axis preponderant orientation of this seismic sequence agree with the characteristics of the tectonic stress field of the focal area and its surroundings.

Research on Stress Drops and the Focal Mechanisms of the Xinyuan- Hejing ML6.8 Earthquake Sequences

Based on the digital waveform data recorded by Xinjiang Digital Seismic Network for the Xinyuan-Hejing M_L6.8 earthquake sequences of June 30,2012,this paper analyzes the stress drops of earthquake sequences and the correlation coefficients of focal mechanisms significant for strong aftershocks.Firstly,the source parameters of the Xinyuan-Hejing M_L6.8 earthquake sequences are obtained by applying the spectrum analysis and the Brunes source model.Then,the correlation coefficients of spectral amplitudes are calculated using the low-frequency spectral amplitude recorded by the same station for the different events.Finally,based on the results of the correlation coefficients of spectral amplitudes,the events with similar focal mechanisms are grouped using the clustering method.The results show that:(1)The stress drop values show a steady trend in the aftershock sequence calm period and the stress drop values show a rise-fall in strong aftershocks.(2)The moving average correlation coefficient of amplitude spectrum begins to spread after the main shock.It shows that the correlation decreases between the main shock and the aftershocks in mechanisms.(3)The results of focal mechanism groups show that the earthquake sequences are mainly strike slips.The stress distribution of the main pressure axis is nearly NS,which is the same as the structural stress field.(4)The magnitude and mechanism show that there is an agreement before the strong aftershock,which shows that the regional stress field is enhanced.

Consistent Distribution of Stress before Strong Earthquake from Focal Mechanisms

At some stage of a strong earthquake preparation, the focal mechanisms of small earthquakes have roughly the same direction with the tectonic stress field. According to this feature, we define the angle between P, B and T axis of focal mechanisms and the three stress axes of tectonic stress field as the consistency parameter a in studying the dynamic changes of stress fields in earthquake preparation areas. We mainly analyze the changes of the consistency parameter a of the Mw8. 3 Knril island arc earthquake and the Mw8. 4 Peru earthquake. Our study shows that before the strong earthquakes, the earthquake area saw a low consistency, and the focal mechanisms of a series of small earthquakes had small differences in the directions with the tectonic stress field, which means the foreshocks were under the control of the stress field. On the other hand, a higher consistency means the focal mechanisms of their aftershocks are scattered and have big differences in the directions with the tectonic field, which indicate that the control of background stress field starts weakening.

Focal mechanisms of the Lushan earthquake sequence and spatial variation of the stress field

Using broadband seismic records from regional networks, we determined the focal mechanisms and depths of 37 earthquakes in the 2013 M7.0 Lushan earthquake sequence(3.4≤Mw≤5.1) by fitting the three-component waveform data. The results show that the earthquakes are predominantly thrust events, with occasional strike-slip mechanisms. Most earthquakes occurred at depths of 10–20 km. We derived the regional distribution of the average stress field in this area using the damped linear inversion method and the focal mechanisms obtained in this study. The inversion results suggest that the Lushan region and the adjacent area are mostly under compression. The orientations of the maximum principal axes trend NW-SE, with some local differences in the stress distribution at different depths. Compared with the distribution of the stress field in the Wenchuan earthquake area, the stress field in the southwest section of the Longmenshan Fault zone(LFZ) share similar characteristics, predominantly thrust faulting with a few strike-slip events and the maximum compression axes being perpendicular to the LFZ.