The multi-point fracturing of oil well vertical to the orientation of the maximum principal stress can improve development effectiveness of the ultra-low permeab.

The soil cutting experiment indicates that the interior friction angle and the shear intensity of soil is reduced;and the maximum principal stress is decreased due to the vibration load;it induces the decrease of digging resistance.

Because there was dissension in the maximum principal stress orientation obtained by in-situ stress measurements by different results measurements,the principal stress axis was determined by conjugate joints,fault occurrence,rake angle and shift symbol of fault slip.

This paper proposes two identification methods of maximal principal stress and its orientation by analysing the stress formula of bevelface.

The critical J integral and the maximal principal stress under joint intensity theory was used as the criteria of crack starting of con-rod,the stress,plastic strain and displacement field were analyzed,and the distribution of crack starting points were displa.

Based on the stresses calculated, the maximal principal stress was taken as the control criterion of the effects of H/B and the distance between bridle rods on the stress of cross section of aqueducts, and the relationship between the aqueduct stress and the rod distance was derived.

Through the differential expression,the variation of maximal radial stress in flange region for circle sheet drawing is discussed and compared with the method by qualitative explanation.