山东某煤矿老采空区上方大型工程建设案例

A case of large buildings construction above oldmine goaf in Shandong Province

以山东某采煤塌陷地为例,开展了煤矿采空区上方大型工程建设研究和实践。通过调查与测绘,高密度电法、大地电磁法、瞬变电磁法等多种地球物理勘查方法和钻探相结合的方法对老采空区进行了精细勘查,获得了4,9,10-2煤3层采空区分布位置、重叠关系、采出率、积水性等参数,揭示了老采空区赋存特征。从地表残余变形对建筑物稳定性影响以及建筑荷载对采空地层稳定性影响2个方面分析了拟建大跨度数据处理中心、4栋高层等建筑物场地稳定性,研究范围内地表因老采空区活化导致的附加变形中附加下沉值为260 mm,超过了拟建建筑修建和使用期间的地基变形要求;9煤层采空区裂缝带与上方高层建筑荷载附加应力影响范围在研究区西部存在重叠区域,部分区域的建筑物地基稳定性差,需要进行采空地层加固治理。采用垂直剖面法确定治理水平治理范围、根据采空覆岩运动特征确定垂直治理范围,依据各煤层采空区间距划分2个注浆层位,注浆钻孔在地面东西走向间距为25 m,南北走向间距为20 m,帷幕孔间距均为15 m,帷幕、注浆孔均一次成孔。采用“无压自流+加压扩散”注浆技术与工艺进行采空地层加固治理,一个注浆层位采用一次注浆工艺,多个注浆层位采用上行式注浆工艺;通过钻孔冲洗液漏失、钻孔取心进行单轴压缩试验、二次注浆等方式检验注浆加固治理效果,钻孔冲洗液无漏失或少量漏失,结石体单轴抗压强度均在9 MPa以上,各钻孔二次注浆量均小于周边钻孔注浆量平均值的10%,所注浆液有效充填了采空地层。分析了采空区地表变形对拟建的高层建筑和大跨度数据处理中心稳定性影响,高层建筑稳定性受地表倾斜影响显著,主体建筑基础采用“桩+筏板”形式,并将高层建筑下的部分注浆钻孔作为小桩基以增强其基础稳定性;大跨度数据处理中心稳定性受地表水平变形影响显著,设置基础连系梁和增强上部结构整体强度来增强其抗水平变形能力,数据处理中心修建过程中地面最大下沉5 mm,平均下沉速度0.01 mm/d。目前研究区内建筑物已投入使用,运行稳定。实现了大跨度、高标准数据处理中心以及22层综合楼等大型建筑群在3层采空区上的安全修建与运营。

A case of large buildings construction site over old mine goaf in Shandong was studied.The fine exploration of the old mine goaf was carried out through investigation and mapping,high density resistivity method,magnetotelluric method,transient electromagnetic method,other geophysical exploration methods and drilling methods.The distribution position,overlap relationship,recovery rate,water accumulation and other parameters of the three-layer goafs of 4,9,10-2 coal seams were obtained,and the characteristics of the old mine goaf was revealed.The site stability of the proposed large-span data processing center and four high-rise buildings was analyzed and evaluated from two aspects:the impact of surface residual deformation on the stability of buildings and the impact of building load on the stability of goaf strata.The additional ground subsidence value caused by the activation of the old goaf in the study area was 260 mm,which exceeds the requirements of the foundation deformation during the construction and the usage of the proposed buildings.There was an overlap area between the 9 coal seam goaf fracture zones and the additional stress influence range of upper high-rise building load in the western study area.The stability of the building foundation in some areas was poor,and it was necessary to reinforce the goaf strata.The vertical section method was used to determine the horizontal governance range,and the vertical governance range was determined according to the movement characteristics of mined-out rock.Two grouting layers were divided according to the spacing of goaf in each coal seam.The spacing of grouting boreholes in the east-west direction was 25 m,and in the north-south direction was 20 m.The spacing of curtain holes was 15 m,and the curtain and grouting holes were completed once.The“pressureless flow+pressurized diffusion”grouting technology and process were used to reinforce the goaf stratum.One grouting layer adopted one grouting process and multiple grouting layers adopted upward grouting process.The grouting reinforcement effect was tested through the leakage of drilling flushing fluid,the uniaxial compression test of drilling core and the secondary grouting.There was no leakage or a small amount of leakage of drilling flushing fluid,and the uniaxial compressive strength of the stone body was above 9 MPa.The secondary grouting amount of each hole was less than 10%of the average grouting amount of the surrounding hole,the grout was effectively filled in the goaf strata.The influence of surface deformation in goaf on the stability of proposed high-rise buildings and large-span data processing center was analyzed.The stability of high-rise buildings was obviously affected by the inclination ground,and the main building foundation adopted the form of“pile+raft”,and some grouting holes under high-rise buildings were used as small piles to enhance the foundation stability.The stability of the large-span data processing center was obviously affected by the horizontal deformation of the ground.Setting the foundation connecting beam and strengthening the overall strength of the upper structure were used to enhance its ability to resist horizontal deformation.During the construction of the data processing center,the maximum ground subsidence was 5 mm,and the average subsidence speed was 0.01 mm/d.At present,the buildings in the study area have been put into use and operated stably.Large buildings were safely built and operated above three-layer coal seam gobs,which include a large-span,high standard data processing center and 22-storey complex buildings.