Microscopic properties and sealing performance of new gas drainage drilling sealing material

The geological condition of Chinese coal mines are complex and high gassy,which account for ffty percent to seventy percent.Because of the abundant pores and cracks around the drainage drilling hole,the gas concentration attenuates rapidly,and the effective gas drainage period is short.The traditional sealing materials of yellow mud and cement-sand grout will readily shrink after the drilling hole is sealed,the sealing length is short and the sealing quality is not satisfactory.Currently widely used polyurethane material will shrink when it comes into contact with water,and the price is also very high.In this study,taking cement as a base material,a novel composite sealing material mixed by expansion admixture,additive,and fbrin and coupling agent was developed and the sealing performance and expansion property of the material were also studied and analyzed.The FEI Quanta TM 250 environmental scanning electron microscope was used to investigate the microstructure of material.The results revealed that the new composite sealing material had a desirable expansion performance and a defnite fluidity convenient for grouting.The solidifed material,combining closely with the drilling wall,possessed an adequate strength and was not easy to shrink.Compared to the conventional polyurethane,the gas drainage concentration by drilling sealing exceeded 40 percent,and the sealing capacity improves5 times,the sealing effect increases signifcantly.

Effects of geotextile envelope and perforations on the performance of corrugated drain pipes

Subsurface drainage is an important agriculture drainage measure.It is primary to select suitable drain pipes and envelopes for efficient subsurface drainage.And now,corrugated drains and geotextile envelopes are widely used.However,the effects of geotextile envelopes and perforations on the drainage of corrugated drains are not well understood.This study conducted a series of sand tank experiments of steady-state flow with or without geotextile envelopes and with different perforation patterns.The drainage flow and the profile head distributions were analyzed and compared.Furthermore,the applicability of theoretical formulas,which are used to calculate effective radius considering the resistance of different perforation patterns,was evaluated.Results showed that the geotextile envelope weakened the effect of perforations on streamlines,thereby causing the value of effective radiuses to be close to that of the actual radius.The drainage flow of the drain with a geotextile envelope was six times that of the bare drain.The relationship between drainage flow and opening area could be described by inverse proportional function.Meanwhile,the drainage flow was affected by the perforation arrangement.Drain with small longitudinal perforation spacing had a drainage flow of approximately 15%larger than that with wider longitudinal perforation spacing.The bottom perforations drained out first and most,and the drainage flow of the drain opened at the bottom could be 11%higher than that at the top.Low-efficiency perforations cause higher head loss near the pipe wall.Existing formulas of entrance resistance were not suitable for geotextile-wrapped corrugated drains,the effect of geotextile envelope and orifice entrance loss at perforations should be considered.