套管超前护壁、管内取样，抽筒是一常用的取样工具。虽然方法简单，所选用抽筒的尺寸或操作不当时，往往出现超样、采样不足以及采不上样等情况，因此，对抽筒与套管的配合尺寸、结构等提出探讨意见。一、抽筒取样的基本原理抽筒借助于自重冲击，插入砂砾样一定深度后，快速提升抽筒，瓣阀关闭，使抽筒底部形成抽吸，并使瓣阀下部到抽筒管脚的砂砾样，随着抽吸而形成抛射、上升。抽吸所产生的负压，促使抽筒与套管的环 Casing ahead of the wall, the tube sampling, extraction tube is a commonly used sampling tool. Although the method is simple, when the size or operation of the selected barrel is not suitable, over-sampling, undersampling and sampling are not always performed. Therefore, suggestions are made on the matching dimensions and structure of the barrel and the casing. First, the basic principle of the drawer sampling The drawer with self-weight impact, insert a certain depth of gravel, the rapid promotion of the barrel, the flap valve closed, so that the bottom of the pump to form a suction, and the lower valve to the pump tube pin Gravel-like, with the aspiration to form a projectile, rising. Suction negative pressure generated to promote the casing and casing ring