龙门县某石灰岩采石场帷幕止水工程及注浆效果评价

龙门县石灰岩储量丰富，是广东省最大水泥生产基地之一。采石产业带动当地经济快速发展的同时产生了一系列环境地质问题。某石灰岩采石场前期对矿区环境地质条件研究程度不足，在开采过程中意外揭穿断裂F1控制的岩溶导水裂隙带，北侧地下水向采坑排泄，涌水量约3 000 m3 ? d-1。随着地下水位的下降，矿区北部陆续产生17处岩溶塌陷，引起多座房屋开裂，对当地居民的生产生活安全造成威胁。文章基于地面岩溶水文地质调查，运用地球物理勘探和钻探等方法，探明该区域地下岩溶发育分布特征，制定帷幕止水方案，并采用综合检测方法（高密度电阻率法、钻孔抽芯、压水试验和地下水位动态监测）对帷幕的注浆效果进行评价。帷幕两侧地下水位动态监测可以综合反映止水效果及其随时间的变化，建议保留监测设备，继续做好监测工作。检测结果表明，浆液基本完成对帷幕轴线方向上溶洞、岩溶管道、裂隙的填充，帷幕两侧形成稳定的水位差，涌水点的流量明显减小，帷幕的止水效果显著。 

Groundwater sealing by grouting curtain technique and its grouting effect evaluation of a limestone quarry in Longmen county

Limestone has a wide range of uses and is an indispensable raw material in people's life. The main uses include cement， chemical fertilizer， medicine， glass， etc. With the acceleration of urbanization and infrastructure construction， the demand for building materials has increased， and the development of quarrying industry has made great contributions to the national economy. However， due to the lack of study on the environmental and geological conditions of mining area in the early stage of the quarries， frequent and unreasonable mining activities have damaged the ecological environment around the mine， resulting in serious environmental and geological problems. Longmen county is rich in limestone reserves and has many limestone quarries，making it one of the largest cement production bases in Guangdong Province， China. A local limestone quarry accidentally exposed the karst water flowing fractured zone controlled by fault F1 during the mining process， and the groundwater in the north side was discharged to the mining pit， with a water inflow of about 3，000 m3 ? d-1. With the decline of groundwater level， 17 sinkholes occurred in the northern part of the mining area， causing multiple houses to crack and threatening the safety of local residents. Based on the ground karst hydrological survey， this paper used geophysical exploration and drilling methods to explore the distribution characteristics of underground karst development in this region， formulated the grouting curtain scheme，and used comprehensive detection methods，such as high-density resistivity method， verification borehole， Lugeon test and groundwater level dynamic monitoring， to evaluate the grouting effect of the water-proof curtain. Based on the understanding that the water-conducting fault F1 was the main inflow channel of groundwater in the mining pit，it is proposed that the purpose of preventing karst collapse can be achieved by sealing with the curtain grouting technique. The location of the curtain was determined by existing site characteristics，geological conditions， sinkhole location， geophysical testing， exploratory drilling and other factors. The curtain was perpendicular to the fault F1， about 200 m long，with a single row of boreholes and a distance of 10 m. Two major void zones were discovered during drilling. The formations of the west void zones were closely related to the fault position， and the east void zones were developed at the stratigraphic boundary. Conventional cement grouts were used in the curtain， and the grout is prepared according to the rock permeability obtained from the Lugeon test. Once the borehole orifice was closed， the grouts were circulated in the borehole， and the upward and downward directions were connected with segmented grouting. This grouting technique achieved a constant grouting pressure and effectively controlled the diffusion radius of the grouts. After the completion of the curtain， the comprehensive detection methods （high-density resistivity method， verification borehole， Lugeon test and groundwater level dynamic monitoring） were used to evaluate the grouting effect of the curtain. The grouting effect detection results showed that， （1） Comparing the apparent resistivity section maps before and after grouting， the apparent resistivity of the soil and karst development areas after grouting were lower than before grouting， and the apparent resistivity curve of the original low resistivity anomaly in the horizontal direction became flat. According to the core photos of the verification borehole，the cement slurry stones was found in the fracture zones and karst caves at different depths. （2） According to the longitudinal distribution of permeable rate obtained from Lugeon tests， the upper rock masses had relatively large permeable rates affected by faults， and it was the layer where dissolution fractures and karst caves were developed；While， the permeable rates of the lower rock mass were relatively small， and the fractures were not developed， so it was a relative aquifuge. The weighted average permeable rates of the verification boreholes were significantly lower than that of the adjacent grouting boreholes before grouting， indicating that the grouts in the grouting areas had a good effect on the filling of karst fractures. （3） The groundwater monitoring data showed that the groundwater level difference on both sides of the curtain was significantly different before and after grouting， and the backwater amplitude of the groundwater level on the north side of the curtain was significantly greater than that on the south side. The groundwater levels on both sides of the curtain had different responses under drilling construction and rainfall conditions， indicating that the curtain cuts off the hydraulic connection of groundwater on both sides and the water sealing effect of grouting was obvious. A stable groundwater level difference formed on both sides of the curtain， and the inflow rate reduced from 3，000 m3 ? d-1 to approximately 500 m3 ? d-1. The dynamic monitoring of groundwater level on both sides of the curtain could comprehensively reflect the water sealing effect and its change over time. It is suggested to retain monitoring equipment and continue the monitoring work.