Analysis on surface cracking causes by high cutting and shallow depth coal mining

in order to maser the surace cracking develogment law of the high cutting and shallo w depth mining,.based on No.22001 cal mining face in Chaohua/Mine as the study object theste monitring and theoetical analysis were applied to obtain the surface cracking distrbution features and the deformaton parameters and to analyze the formation causes of the surace discontinuous deformaton. The resuits showed that the pilot distance of the dynamic cracking was 38.5 m and the development period was 19 days.The cracks fnally would have the features with high density.narrow width,no bench type development.small compresson deformation region and small cracking angle, The breaking of the key layer in he overburden strata was the basic causeof the suface ground cracking ocured. Due to the litholegyof the overburden strata was soft and thelose layer was thick,.the stress was relaxed during the transtion perod and thus the posstilty fthe bench cracking development was decreased.The tensie perormanceof the loess ayer was weak and the surface ground would have the cracking features withdense distributin and no bench development.