Mechanism of roadway floor heave and control technology in fault fracture zone

In terms of the floor heave problem at -650 south wing fully mechanized chamber ( -650 centralized cooling chamber after repair) in Yangcheng coal mine,the influence factors of the floor heave were investigated by field inves- tigation and laboratory test,including the influence of fault fracture zone,the poor quality of floor rock mass,the deteri- oration of floor soaking and the weak support of the floor. Among them,the first two belong to geological factors. The second two belong to human factors. The optimized design and waterproofing should be considered. The formation process of floor heaves under the original support and rework support conditions was simulated by finite element meth- od. It was revealed that the zero displacement mark of roadway floor was about 7 m away from roadway floor and the zero strain mark was about 10 m away from roadway floor. There were three distinct areas in the floor:tensional strain increasing area,tensional strain sinking area and compressive strain sinking area,among which the tensional strain in- creasing area was widely distributed and into great deep area ( that is,the depth of the zero displacement marking), and the continuous displacement of tensional strain increasing area under surrounding rock stress was the key cause of floor heave. The rework scheme optimized the full section support and focused on strengthening the support force of the floor,which greatly increase the zero displacement marking. The simulation showed that the zero displacement mark of the floor after repairing was about 4 m away from the floor of the roadway. Compared with the original support condi- tion,the zero displacement mark increased about 3 m,which reduced the depth of the floor heave,and the effect of the bottom control was good. The mechanism of floor heave was analyzed with the depth of floor zero displacement marking (the depth of floor heave producing area). Under single variable conditions,the correlation function of floor support force,floor rock strength,roadway depth,roadway radius and zero displacement line depth were in accordance with log- arithmic function,power function,linear and logarithm function,respectively. Among them,the effect of floor support force and roadway radius was significant,the effect of floor rock mass strength was second,and the effect of roadway depth was weakest. Therefore,in order to restrain floor heave,the support force of floor should be increased as much as possible under the conventional support conditions;the size of roadway should be reduced as much as possible under the condition that the roadway met the production requirements;the strength of floor rock mass should be maintained or optimized as far as possible for the soft rock floor,and the floor waterproof and drainage must be carried out. Finally, the combined rework support scheme was put forward to optimize the whole section support with anchor net,cable spra- ying and concrete filled steel tube support technology,and reinforce the floor support with reinforced concrete bottom beam. The engineering practice showed that the floor heave was well controlled and the floor heave was less than 20 mm after the rework. The calculation results showed that the supporting force of reinforced concrete bottom beam was 1. 02 MPa,that of concrete filled steel tubular support was 0. 91 MPa,and that of the repairing scheme is 1． 93 MPa,which belongs to the high supporting force scheme. But the repaired support also was complicated in construction and high in cost. Therefore,an optimized support system composed of prefabricated arc plate,controlled bottom anchor cable and waterproof layer was proposed,which was simple in construction and low in cost.