Test And Research On Reinforcing The Soft Coal Under Backfill Of Gob-Side Entry By Rotary Jet Grouting Method

Rotary jet grouting method has the advantages of simple equipment,convenient construction,high speed,high efficiency,and low cost,and its application has become increasingly mature in foundation reinforcement.Research on the method employed in the construction of mine to support the flexible formwork concrete walls is first time,which will improve and develop the application of flexible formwork concrete support technology.The formulation of grouting material is an essential part of the rotary jet grouting method.Whether it is reasonable or not will directly affect the physical and mechanical indexes,chemical stability of consolidation block formed by rotary jet grouting method and project cost.In order to apply the method to reinforce roadway floor below the flexible formwork concrete wall in mine,studying grouting material mechanical index with a laboratory test.Water-cement ratio and cement content affected significantly on the compressive strength of consolidation block,and the effect of water-cement ratio on compressive strength of consolidation block is greater than that of cement content.When Water-cement ratio is 0.8,the cement content in the consolidated body should not be less than 30%,otherwise pile-forming effect will be affected.Proper amount of early strength agent can increase the compressive strength of the consolidated bodies in 7d.But when the early strength agent reaches 2%of the cement mass,the compressive strength of the consolidation bodies in 14d and 28d decrease in different degree.So when the engineering project has no higher requirements on the compressive strength of 7d,early strength agent should not exceed 1%of cement mass.In addition,fly ash with cement mass of 10%will reduce the compressive strength of the consolidated body by nearly 10%in 7d and 14d,The amount of fly ash can not exceed 20%of cement mass,otherwise compressive strength of the consolidated body will have greater degree.Compound admixture extend the setting time and decrease the compressive strength at the same age.What's more,compound admixture has the same effect on the final setting time and the initial setting time,which is different with that of fly ash and water-cement ratio.The effect of fly ash and water-cement ratio on the final setting time is much greater than the initial setting time.The increase of the setting time of the consolidation body is due to retarding effect of the compound admixture,and the reason for the decrease in the compressive strength is the decrease in setting rate of the consolidation body.Compound admixture has more influence in setting time than water-cement ratio that is much greater than fly ash.For the specificity of underground coal mine construction,the corresponding rotary jet construction equipment and its construction technology were developed.The equipment in the industrial application test of the No.3603 working face in shanxi huo'erxinhe mine performed well and the reinforcement effect was satisfactory.