深厚冲积层钻井井壁底力学特性实验研究

Experimental Study of Mechanical Characteristics at Bottom of Shaft Lining Drilled in Deep Alluvium

用相似材料对钻井井壁底的力学特性进行了实验研究。结果表明：由于削球部位的经向应力较大，该部位出现的破坏裂纹多为沿圆周方向的锯齿状裂纹，并且破坏位置均在削球与支承环交界处；另外由于支承环部位的环向应力较大，井壁底支承环部位出现的破坏裂纹多为与竖直方向呈45°～60°夹角的斜裂纹，由此可见，钻井井壁底的破坏均属压剪破坏。由实验和有限元计算结果可知，井壁底的最危险截面在支承环与削球部位交界处，因此在进行井壁底设计时，可以考虑对井壁底进行局部加强，以减少支承环与削球交界处的应力集中。

An experimental study of mechanical characteristics of drilled shaft was carried out by resemble material. The results of tests showed that the cracks of cutting sphere were dentate around its latitude due to big longitude stress in cutting sphere, and the cracks were in the intersection of cutting sphere with supporting annulus. On the other hand, the angles of the cracks in supporting annulus at bottom of shaft lining are 45°-60° with vertical direction owing to the big annular stress. Thus it can be seen that deconstruction at bottom of drilled shaft lining is due to shearing stress. Based on results of test and finite element analysis, the most dangerous section at bottom of shaft lining is in the intersection of cutting sphere with supporting annulus. In shaft lining bottom design, it can be considered to strengthen the intersection of cutting sphere with supporting annulus to reduce stress concentration.