The blasting fragment size of a mine is required to be less than 0.4 m.However,this area has a geological structure consisting of both hard and soft layers,which makes the traditional blasting method easy to produce boulders,and the blasting quality difficult to meet the requirements.In order to conquer the problem and save the construction cost,blasting tests on square hole layout with both deep and shallow holes were carried out with the middle shallow hole depths of 0 m,4 m,5 m,6 m and 7 m.Firstly,ANSYS/LSDYNA finite element software was used to carry out numerical simulations with a limestone model with RHT constitutive relation in the upper part and a marl model with HJC constitutive relation in the lower part,forming a hardsoft interlayer structure.Then,numerical tests were conducted to initially obtain more optimal middle hole depths,and the distribution characteristics of rock mass damage and the distribution law of blast effective stress under different test conditions were analyzed.Since ANSYS/LSDYNA does not take the effect of detonation gas into account,the middle shallow hole depths of 4 m and 5 m were selected for onsite blast tests in order to obtain more accurate experimental conclusions and not to excessively increase explosive consumption.The research results show that it is effective to reduce the blasting boulder yield by square hole layout combining deep and shallow holes.When the depth of the middle shallow hole is 5m,the curvature coefficient Cc and the boulder yield can be reduced.Before the technology optimization,the average boulder yield was about 64.4%,and the rate of fragments larger than 0.4m have been reduced to about 38.1% after the technology improvement,making the blast fragmentation to a favorable level.So,the scheme of 5 m shallow holes has a better effect of reducing boulder yield than the original blasting scheme and the scheme of 4 m middle shallow hole.