采空区保护煤柱对下层煤开采覆岩移动影响分析

为能够更进一步确定采空区保护煤柱对下层煤开采覆岩移动的影响,采用数值模拟测试方法对位于不同起始位置保护煤柱随着采空区下开采面的不断推行,研究上覆岩层的离层空间、动压显现特征以及"三带"开裂高度。经过本次的模拟测试的实验结果表明,在开采面上方的上部顶板岩层中间的拉伸破坏单元一步步增多,加剧工作面上部顶板的断裂和塌落,同时也减小了上部顶板之间的断裂布局。煤层保护性煤柱距离开采面的起始位置越近,则第一次来压期间的位移将会越增大,使裂隙向上发展的高度进一步增大,表明采空区下近距离煤层在开采过程中增加了"上三带"的发展。

混凝土板柱节点弯曲裂缝截面冲切承载力验算方法研究

混凝土板柱结构中,板柱相连截面同时作用较大弯矩和冲切剪力,为主要设计控制部位。《混凝土结构设计规范》(GB 50010-2010)中板的冲切承载力验算方法,未考虑弯曲裂缝减小验算截面的不利影响,可能导致验算结果偏于不安全。结合混凝土板柱结构中节点弯剪破坏工程实例,基于GB 50010-2010规范相应公式,提出了混凝土板柱节点开裂截面冲切承载力验算方法,通过算例说明了相应验算过程且与规范验算结果进行了比较,并配合技术分析给出了相关设计建议,由此初步探索了如何避免裂损促使板柱节点发生脆性冲切破坏,结果可作为规范方法的补充供结构设计参考。

Effect of anions on stress corrosion cracking behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo

The effects of chloride,sulfate and carbonate anions on stress corrosion behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo were studied by stress corrosion cracking(SCC)test method using double cantilever beam(DCB)specimens.The SCC morphology was observed by using scanning electron microscopy(SEM)and the composition of corrosion products was analyzed by using energy dispersive spectrometer(EDS).The results show that the crack propagates to bifurcation in NaCl and Na2SO4 solution,while the crack in Na2CO3 solution propagates along the load direction.The SCC rate in NaCl solution is the highest,while lower in Na2SO4 solution and little in Na2CO3 solution.From the SEM morphologies,quasi-cleavage fracture was observed in NaCl and Na2SO4 solutions,but intergranular features in Na2CO3 solution.The mechanism of anion effect on SCC of steel 23Co14Ni12Cr3Mo was studied by using full immersion test and electrochemical measurements.

Fractured zone height of longwall mining and its effects on the overburden aquifers

As mining depth becomes deeper and deeper,the possibility of undermining overburden aquifers is increasing.It is very important for coal miners to undertake studies on the height of fractured zone during longwall mining and the effects of longwall mining on the underground water while mining under surface water bodies and underground aquifers.In order to study this problem,piezometers for monitoring underground water levels were installed above the longwall panels in an American coalmine.Large amounts of pre-mining,during mining and post-mining monitoring data were collected.Based on the data,the heights of fractured zones were obtained and the effects of longwall mining on the underground water were studied.The results demonstrate that when the piezometer monitoring wells had an interburden thickness of less than 72.7 m,the groundwater level decreased immediately to immeasurable levels and the wells went dry after undermining the face of longwall.The height of the fractured zone is 72.7-85.3 m in the geological and mining conditions.The results also show that the calculated values of fractured zones by the empirical formulae used in China are smaller than the actual results.Therefore,it is not always safe to use them for analyses while mining under water bodies.

Overburden failure and the prevention of water and sand inrush during coal mining under thin bedrock

Coal mining under thin bedrock or thick unconsolidated soil layers brings mining problems related to these special geological conditions. The meaning of the term ''thin bedrock'' is defined through the thick- ness statistics of the coal seam and the bedrock layer. The coal-bearing strata having thick, unconsoli- dated aquifers and thin bedrock located at the Taiping Coal Mine in Shandong province were taken as a geological prototype for subsequent study. The geological, hydro-geological and engineering character- istics of the thin bedrock were analyzed. An engineering geological model was than established. Overbur- den failure and the development of ''Three Zones'' were studied by physical model tests. The rupture pattern and rock failure were analyzed for mining conditions under thin bedrock. The height of the caving zone and the freely flowing water fractured zone of different mining thicknesses were separately calcu- lated. The results show that a mining thickness greater than 3.5 m causes the height of the freely flowing water fractured zone to be sufficient to touch the weathered zone and the bottom of the Quaternary sys- tem aquifer, to various degrees. This, then, would lead to water and sand inrush into the working face. Measures to prevent water and sand flow inrush disasters by eliminating the power source are put fore- word. A field dewatering scheme was designed and observational data were obtained. The dewatering project had an obvious effect and the water level at working face number 8309 dropped to a safe level. The average draw down of the groundwater was observed to be 7.86 m. This showed that the dewatering project played a role in decreasing the hydraulic pressure and ensuring safety mining.

The test research on partial relieving pressure for the entry in the deep mine under high stress and friable surrounding rock

Based on the geological condition of Zhangxiaolou deep mine in Xuzhou mining area, under 986 m in depth, 20.6-31.6 MPa in maximum horizontal principal stress, and friable and fractured surrounding rock, test researches on partial relieving pressure were completed for the entry with U-steel arched yielding support. The relieving pressure parameters, technology process and results of springing blasting by boreholes and excavating pockets in the two sides of entry were introduced. It is demonstrated that springing will not be shaped under the condition of single borehole arrangement after exploded, the arrangement by a group, it will make borehole bottom form springing in 0.6-0.8 m in diameter, that convergence of two sides and roof to floor have some increments by using springing blasting for reliving pressure. This kind of method for reliving pressure is not suitable to use in the deep mine, and that the convergence of two sides obviously declined by excavating pocket in two sides, it can be still used in the entry with metal support, while maintenance of entry in deep mines is difficult, and can not be supported by bolt or bolt with wire mesh.

基于监测数据的装配式T梁桥服役状态可靠度的评估方法

为准确把握装配式T梁桥的服役状态,提出基于监测数据的装配式T梁桥服役状态评估方法。首先,采用应变数据并基于平截面假定反算主梁开裂高度,基于纤维模型建立主梁开裂高度和主梁抗力之间的对应关系;然后,基于动态称重系统监测数据,采用Rice公式极值外推法,建立主梁车辆荷载效应概率分布模型;最后,基于可靠度理论,建立主梁抗力和效应之间的功能方程,计算主梁可靠指标,评估主梁服役性能。结果表明,基于主梁应变数据可以计算得到主梁开裂高度,这样避免了传统主梁状态评估中需要人工检测裂缝的缺点,提高了结构评估的时效性;纤维模型可以准确反映截面裂缝开展全过程,基于纤维模型可以建立主梁开裂高度和主梁抗力之间的对应关系;背景桥梁在当前开裂高度和荷载水平下,主梁可靠指标满足要求,说明服役状态良好。