弱富水软岩水-沙混合型突水机制与防治技术——以上海庙矿区为例

近年来我国西北侏罗纪煤田弱富水软岩水-沙混合型间歇式突水事故多发,短时水(沙)量大,缺少有效的防范技术措施,严重威胁矿井安全生产。为揭示其形成机制以便于制定相应的防范措施,以内蒙古上海庙矿业新上海一号煤矿为研究对象,室内测试了岩石力学强度、软化系数等参数,井下实测了围岩松动圈,综合判定为典型的软岩地层;正交偏光镜下显示砂岩成熟度低,黏土质矿物胶结;水理性试验表明砂岩颗粒间泥质胶结物易产生溶蚀现象,能够形成固-液双相混合物,在水动力下具有流沙属性;泥岩极易吸水膨胀、泥化。根据含水层水位和地表岩移长期观测结果,推定低位覆岩内和高位覆岩内均可以产生离层裂隙,且离层裂隙具有汇集水源功能。将111084工作面突水溃沙过程中含水层水位历时曲线与水量历时曲线叠合考察,突水量与突水含水层水位升降变化之间有明显的相关性。初时突水量大、水位下降幅度也大;水量在趋于衰减过程中出现几次跃升,含水层水位在趋于回升过程中出现几次相应的跃降;跃升(跃降)的幅度梯次减小;两次跳跃时间间隔梯次延长。综合以上信息,提出离层裂隙的汇水作用可以强化弱含水层短时突水强度观点,弱胶结砂岩提供了混合突水的沙源;离层水体释放过程中水动力发生强弱变化,随着离层水体释放水动力减弱,大量泥沙封堵突水通道,表现出泥沙自封堵效应。覆岩持续压缩,离层裂隙储水能力逐渐弱化,表现为突水量梯次减小;离层水补给路径逐渐扩展,表现为突水休止期梯次延长。汇水—突水—封堵—再汇水—再突水—再封堵的过程交替进行,揭示了间歇性水-沙混合型突水模式的突水机制。离层水害发生需要具备水源(富水性)、时间、空间、通道、压力等5个必要条件,强调导水裂隙突水通道的重要性。工程应用表明,顶板水预疏干可以改变含水层的富水性条件,预置导流管改变离层空间封闭性和汇水时间条件,突水通道和压力条件,可以有效避免此类事故发生,保障矿井安全生产;同时可实现无顶板淋水、采空区无涌水状态下开采,优化采场作业环境、弱化软岩劣化效应,促进矿井高效生产。

Mechanism and prevention of water sand inrush in soft rock with weakly abundant water:A case study in Shanghai temple mining area

There are many water sand inrush incidents with intermittent characteristics in soft rocks with weakly abundant water in the Jurassic coalfield in recent years.Large amount of water (sand) in a short time,and lack of effective technical preventive measures seriously threaten a safe coal production.In order to obtain the mechanism of water sand inrush and to formulate effective preventive and control measures,a case study was conducted at New Shanghai No.1 Mine.The parameters such as rock mechanical strength and softening coefficient were tested in the laboratory and the rock was synthetically identified as a typical soft rock formation.Orthogonal polarizers show a low maturity of sandstone,and a clay mineral cement.Hydrological tests show that the mud cement of sandstone particles are prone to erosion,can form a solid liquid bipolar mixture,and shows quicksand properties under hydrodynamic conditions.Mud stone easily absorbs water,expands and becomes muddy.Based on the long term observations of aquifer water level and surface rock movement,it is assumed that delamination can occur in both low and high overlying rocks.In addition,the delamination fissure has the function of collecting water source.Considering the overlap of the water length curve and the water length curve of the aquifer in the process of sand breaking in 111084 working surface,there is obvious correlation between the water burst and the change of water level in the aquifer.At the beginning,there is a large amount of water and the water level drops significantly.There are several jumps in the process of water volume decreasing,meanwhile several corresponding jumps in the water level of the aquifer during the process of rising.The amplitude of jumps (drops) decreases.The interval between the two jumps is extended.Based on the above information,it is proposed that the effect of water collection in delamination fissure can strengthen the short term water burst strength of weak aquifer,and weak cemented sandstone provides a source of mixed water inrush.Water dynamics change during the release of delamination water.With the release of water,the power of water release decreases,and a large amount of sediment seals the water burst channels.It shows a self sealing effect of sediment.As the overburden continues to compress,the water storage capacity of delamination layer is gradually weakened,showing a sudden decrease in water level.The progressive expansion of delamination layer water recharge routes,showing a terraced extension of the water burst rest period.The process of recharging flooding plugging recharging replugging is alternating.The water burst mechanism of intermittent water sand mixture is revealed.The occurrence of delamination layer water damage requires five necessary conditions such as water source (water rich),time,space,channel,and pressure,emphasizing the importance of water diversion channel for water diversion fissures.The application practice shows that pre drying of roof water can change the water rich condition of the aquifer.Changing the water inrush channel and pressure condition with prearranging guide tube,this kind of accident can be prevented effectively,ensuring the safety of mine production.At the same time,it can realize mining without water dripping from the roof and in the goaf area,optimize the operating environment of the mining face,weaken the soft rock effect,and promote the efficient production of the mine.