Research on the bearing performance of grouted steel pipe piers and their application in gob-side entry retaining under fully mechanized top-coal caving mining

Li Huaizhen; Li Jiahao; Yuan Ruifu; Mu Bangbang; Xie Shuaishuai

doi:10.16186/j.cnki.1673-9787.2025030007

Abstract：Objectives The use of filling materials for roadside support in gob-side entry retaining under fully mechanized top-coal caving mining is often associated with large material transportation volumes,com-plicated construction processes,low early strength,and high costs.Therefore,there is a strong need to de-velop a high-strength,high-stiffness,lightweight,and modular roadside support structure.Methods The bearing performance of grouted steel pipe piers was investigated through theoretical analysis,laboratory ex-periments,numerical simulations,and engineering application.Steel pipe specimens with a length of 500 mm and a diameter of 159 mm,fabricated with different wall thicknesses and grouted with slurries of vari-ous water–cement ratios,were subjected to axial loading tests and numerical simulations to identify the key factors influencing bearing capacity and to determine reasonable design parameters.Based on structural optimization,steel pipe piers with a length of 1 200 mm and a diameter of 159 mm were manufactured and grouted with a slurry at a water–cement ratio of 0.4,followed by axial loading tests and numerical simula-tions.Furthermore,taking a gob-side entry retaining project in a fully mechanized top-coal caving working face as the engineering background,the bearing performance of field-used grouted steel pipe piers(length 3 000 mm,outer diameter 299 mm,wall thickness 8 mm,water-cement ratio 0.4)was analyzed using the limit equilibrium method and numerical simulations.Results The results indicate that a steel pipe wall thickness of 8 mm combined with a water–cement ratio of 0.4 provides an optimal ultimate bearing capac-ity for the grouted steel pipe piers.The axial ultimate bearing capacity of the piers applied on site exceeded 4 800 kN,which is in excellent agreement with theoretical predictions.Conclusions By optimizing the steel pipe wall thickness and slurry mix proportion,grouted steel pipe piers exhibit high bearing capacity while simplifying the construction process and reducing equipment requirements and material costs.Engi-neering practice demonstrates that when grouted steel pipe piers are applied for gob-side entry retaining un-der fully mechanized top-coal caving mining,the maximum convergence between the roof and floor is 78 cm,and the maximum convergence of the roadway ribs is 95 cm after stabilization,meeting the engineer-ing requirements for roadway deformation control.