水文地质钻探的主要对象是第四纪松散地层和基岩（石灰岩），其中卵石层是常见的地层，甚至有的机台全年均在卵石层中施工。卵石层以卵石、砾石为主，组织不均匀，孔隙度较大，孔隙中充填有砂或粘泥。结构松散，容易坍塌掉块。不仅钻进效率低，而且取心困难。对于水文地质钻探，岩心不仅是划分地层、鉴别岩性的一种重要根据，而且是成井工作中选择井管和砾料规格的依据。即使对取心率无要求，坚硬而较大的卵石取不出来也不能进尺。我队过去卵石层取心曾用投卡条、干钻、无泵、投球单管钻具、钢 Hydrogeological drilling mainly targets Quaternary loose strata and bedrock (limestone), of which the pebble bed is a common formation, and some are even constructed all year round in the pebble bed. Pebble layer to pebbles, gravel-based, non-uniform organization, a larger porosity, porosity filled with sand or sticky mud. Loose structure, easy to collapse off the block. Not only is drilling inefficient, it is difficult to corout. For hydrogeological drilling, the core is not only an important basis for stratigraphy identification and lithology identification, but also the basis for selecting the specifications of well tubular and gravel for well-formation work. Even if the heart rate is not required, hard and larger pebbles can not get out and can not enter the ruler. Pebble layer coring in my team used to vote card, dry drilling, no pump, pitching single tube drill, steel