砂土地层泥水盾构泥膜形成时间及泥浆压力转化率的试验研究

泥水盾构施工中,维持开挖面稳定的关键是要在开挖面及时形成微渗透的泥膜,才能将泥浆压力转化为有效应力来平衡开挖面的土压力。开挖面处的泥膜是动态泥膜,所以泥膜的形成时间是影响泥膜能否有效支护开挖面稳定的重要因素。利用自行设计的泥膜形成时间测量试验装置,在3种地层中,利用5种泥浆开展泥浆渗透成膜试验,研究泥膜的形成时间及相关规律。研究表明,在泥皮型渗透中泥膜的形成时间一般为10 s左右,泥浆性质及粒径对泥膜的形成时间有重要影响。讨论了国内外部分大型泥水盾构泥膜形成时间,发现泥膜从破坏到形成、再到破坏的时间间隔为5²0 s不等,因此,在实际施工中需要调整泥浆性质,使泥膜形成时间小于泥膜从破坏到再破坏的时间。

Experimental study of forming time of filter cake and conversion rate of slurry pressure in slurry shield in sand stratum

In slurry shield construction, forming a filter cake in time is important for working face stability; the slurry pressure could be transferred into effective stress with filter cake then acting on the working face. The filter cake on the working face is dynamic, thus the forming time of filter cake is the main factor which could affect the supporting for working face. An apparatus is designed which could measure the excess pore pressure in the stratum. Infiltration tests are done in three kinds of high permeability strata with five kinds of slurry to study the forming time of filter cake, its supporting ability and the influencing factors. The results indicate that the forming time of filter cake is 10 seconds in only filter cake infiltration styles. The slurry property and the grain size of stratum have important effects on the forming time of filter cake. The filter cake forming time in part of large slurry shields at home and abroad is also discussed; and the results indicate that the time from destruction to re-destruction of filter cake is ranged from 5 seconds to 20 seconds; thus the property of slurry should be suitable to ensure that the forming time of filter is less than the time from destruction to re-destruction of filter cake.