In this paper, the experiments of comeback and comeback holding pipe have been performed, then the SME characteristic values of Fe-Mn-Si-Cr SMA sleeve in the case of different ratio of expanding diameter have been tested and analyzed.

The prediction technology of hole enlargement ratio in the condition of underbalanced drilling;

Effect of friction on deforming condition during tube expanding process;

The method of Prediction for the spring back of cylinders in mechanical expanding;

The practice of deep well diameter extension and washing, blasting is introduced in this paper.

Based on such analysis,some criteria and methods have been proposed for judging the situation of honeycomb,segregation,reducing,diameter extension,breaking zone and sedimentation on the bed of pile,etc.

Qinghai Electric Power Transmission and Distribution Corporation undertakes the II section of 750kV Ma\'nasi-north of Urumchi transmission line engineering,and construction technics of hole enlargement conductor paying off has been adopted.