| The production capacity of Lilou-Wuji iron mine is 7.5 million t/a,which is one of the large-scale underground metal mines in China.Large structure stope and high efficiency trackless mining have become the basic means to meet the requirements of large-scale mining.The two-step subsequent filling mining method is adopted in the Lilou-Wuji mine,with a level height of 100 m,a room and pillar width of 20 m,and a lateral exposure area of 4000-6000 m2.With the large-scale mining process of the Lilou-Wuji iron mine in the-400 m level,ground pressure disasters such as roof caving,bib spalling and support falling off along the vein roadway seriously restrict the safe and efficient mining of the mine.Therefore,taking the-400 m stope as the engineering background,in-situ stress measurement,stope surrounding rock ground pressure monitoring,filling body internal stress monitoring,FLAC 3D numerical simulation and other methods were applied to comprehensively study the high-level two-step mining ground pressure activity law,focusing on solving the technical problems such as stability of mining large-scale stope and optimization of structural parameters.The main research contents are as follows:(1)The in-situ stress of 12 measuring points at the level of-300 m section,-350 m section and-400 m section in Lilou-Wuji mining area was measured by the front-end digital hollow inclusion strain gauge.At the same time,the multi-regression fitting method was used to simulate the spatial distribution of the geostress field in the mining area,and the geostress field regression model was established.Combined with the geological structure of the mining area,it was determined that the stress state of mining area was transition from the thrust type to the translation type.(2)Combined with the ground pressure survey of the-400 m level in the Lilou mining area,the ground pressure monitoring position of the high level large stope structure was determined.Through monitoring the surrounding rock ground pressure in four horizontal stopes of one-step 12-1#pillar and two-step 10-4#pillar,it was revealed that the surrounding rock ground pressure in the same level of the stope had three stages:gradual rise stage,pressure stability stage and pressure relief stage.The surrounding rock in the two-step stope space presented the opposite"layered and stepped" transfer law:the one-step stope is "top-down" while the two-step stope is"bottom-up".Based on the independent development on-line stress monitoring device,the three-dimensional stress of cemented backfill in four different sections of the 26-1#stope was monitored in full time,which revealed the three-dimensional stress evolution law of cemented backfill.(3)The relationship between the law of ground pressure activity and the mining operation process in the two-step stope was revealed:when the first-step room was mined,the stress field in the mining area was redistributed for the first time,which was mainly supported by the pillar.When the two-step pillar was mined for the first time,the stress field of the mining area was redistributed for the second time.The reserved ore pillar and surrounding rock were the main bearing objects of the mining area.The capacity of the cemented filling body was not high,but the cemented filling body played a role in providing lateral pressure for the mining field surrounding rock,improving the self-supporting capacity of the surrounding rock.During the second mining process of the two-step pillar,the stress field in the mining area was redistributed for the third time.The surrounding rock of the hanging wall and footwall and the surrounding rock of the north and south ends were the main bearing objects of the mining area.The bearing capacity of the weak cemented filling body and the cemented filling body was not high.However,the weak cemented filling body linked the two cemented filling bodies together,which made the two-dimensional force of the cemented filling body become three-dimensional force and improved the stress state of the cemented filling body,so that the whole two-step mining is safer and more stable.(4)The reasonable exposed area of the high-level large structure stope was determined by the Mathews stability diagram method.Combined with the FLAC 3D numerical simulation,the mining sequence and structural parameters of large structure stope were optimized.It was determined that the original mining method of "take one every the other one" was maintained,and the width was changed to 22m while the length of the ore house and pillar remained 50 m and the height remained 100 m. |
