摘要
评估煤矿顶板水压致裂的起裂水压,需要定量分析致裂过程中水对预制切槽尖端岩石断裂特性的影响。为评估王台铺煤矿石灰岩顶板的起裂水压,分别在天然和饱水状态下对煤矿现场采集的顶板石灰岩样品进行了单轴压缩试验、纯Ⅰ型断裂试验以及Ⅰ-Ⅱ复合型断裂试验。采用ANSYS模拟软件以单轴压缩试验结果为材料参数、以断裂试验峰值载荷为受力条件构建了断裂试验试件的有限元模型,计算了2种状态下顶板石灰岩的Ⅰ型断裂韧度KIC和多组复合型断裂发生时试件裂纹尖端的KⅠ,KⅡ值,获得了2种状态下的复合型断裂临界曲线。试验结果显示:(1)饱水状态下顶板石灰岩的各项指标相对于天然状态有不同程度的弱化,Ⅰ型断裂韧度的弱化最明显,其次是抗压强度和弹性模量,泊松比受影响较小;(2)不同状态下顶板石灰岩遵循不同的Ⅰ-Ⅱ复合型断裂判据。通过将顶板水压致裂的预制切槽简化成币型裂缝,结合天然和饱水状态下试验测定的顶板石灰岩各力学参数及Ⅰ-Ⅱ复合型断裂判据,导出了2种状态下起裂水压计算公式。将天然和饱水状态下起裂水压计算值作为真实起裂水压的上下确界,可以评估顶板水力压裂起裂水压的范围,还可以根据地应力优化预制切槽的倾角选取,从而使水力裂缝在相对更低的水压下起裂。在王台铺煤矿XV2307工作面开展了石灰岩顶板水压致裂试验,现场测定的真实起裂水压位于饱水状态计算值与天然状态计算值之间,验证了评估方法的有效性。
The premise of initiation pressure evaluation of roof hydraulic fracturing is to quantitatively analyze the effect of water on the fracture characteristics of rock at the tip of pre-cut notch during fracturing.In order to evaluate the initiation pressure of roof hydraulic fracturing in Wangtaipu Coal Mine,a batch of roof limestone samples were collected,and a series of uni-axial compression tests,pure typeⅠfracture tests andⅠ-Ⅱmixed mode fracture tests were carried out in natural and water-saturated states.Series of finite element models of the fracture test specimens were constructed by ANSYS with the uni-axial compression test results as the material parameters and the peak load of fracture test as the load condition,the typeⅠfracture toughness KIC of the roof limestone and groups of KⅠand KⅡat the crack tip of specimens whenⅠ-Ⅱmixed mode fracture occur were calculated,and the critical curves ofⅠ-Ⅱmixed mode fracture of limestone in natural and water-saturated states were obtained.The test results show that:(1)the indexes of roof limestone in water-saturated state are decreased in different degrees,the decrease of KIC is most obvious,followed by compressive strength and elastic modulus,and Poisson’s ratio is less affected.(2)The roof limestone follows different mixed mode fracture criteria in different states.Based on the test results,a set of initiation pressure evaluation method of roof hydraulic fracturing was proposed.By simplifying the pre-cut notch of roof hydraulic cracking into coin type crack and combining with the mechanical parameters and theⅠ-Ⅱcomposite fracture criteria of roof limestone in natural and water-saturated states,the calculation formulas of initiation pressure under two conditions were derived.Taking the calculated value of initiation pressure in natural and water-saturated states as the upper and lower bounds of the real initiation pressure,the range of initiation pressure of roof hydraulic fracturing can be evaluated,and the selection of inclination angle of pre-cut notch can be optimized according to the in-situ stress,to make the hydraulic fracture initiation under relatively lower water pressure.The measured initiation pressure of roof hydraulic fracturing field test in the coal mine verifies the validity of the evaluation method.A hydraulic fracturing test of limestone roof was carried out in XV2307 working surface of Wangtaipu Coal Mine.The initiation pressure measured on site is between the calculated value of water-saturated state and the calculated value of natural state,which verifies the validity of the evaluation method.
作者
唐铁吾
刘大安
崔振东
韩智超
刘兵权
王之东
TANG Tiewu;LIU Daan;CUI Zhendong;HAN Zhichao;LIU Bingquan;WANG Zhidong(Key Laboratory of Shale Gas and Geoengineering,Institute of Geology and Geophysics,CAS,Beijing 100029,China;Innovition Academy of Earth Science,CAS,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;School of Mechanics and Civil Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2020年第S02期727-735,共9页
Journal of China Coal Society
基金
国家自然科学基金资助项目(41972296,41072242)
关键词
水压致裂
天然状态
饱水状态
Ⅰ-Ⅱ复合型断裂
断裂判据
hydraulic fracturing
natural state
water-saturated state
Ⅰ-Ⅱmixed mode fracture
fracture criterion
