一、地层和钻探施工情况我队钻探施工在沿河地区的平原地带,钻孔大致可分三个孔段.第一孔段是第四系覆盖层,主要岩层有粘土、亚粘土、砂岩、砂页岩和砾石层,厚度140～240米.第二孔段是风化带,其中一部分是矿层风化,厚度30～70米.第三孔段是基岩,主要岩层有磁铁矿、片岩、片麻岩、角闪岩和大理岩等.粘土层引起钻孔严重缩径;砂层、砂砾层因松散无胶结性而容易坍塌;风化带由于 Construction of Stratum and Drilling Our team drilled in the plains along the river, drilling can be roughly divided into three holes.The first hole is Quaternary overburden, the main rock layers are clay, clay, sandstone, Sand shale and gravel, the thickness of 140 to 240 meters.The second hole is the weathering belt, part of the mine is weathered, the thickness of 30 to 70 meters.The third hole is bedrock, the main rock layers are magnetite, schist, Gneiss, amphibolite and marble, etc. Clay layer causes serious hole diameter reduction; sand layer and gravel layer easily collapse due to loose and non-cementing; Weathering belt due to