无水砂层大断面矩形管廊顶管施工渣土改良试验

MUCK IMPROVEMENT TEST FOR JACKING CONSTRUCTION OF LARGE RECTANGULAR CROSS-SECTION PIPE IN ANHYDROUS SAND LAYER

大断面矩形管廊在无水砂层中顶进施工时,由于砂土流塑性差,掌子面易出现"闭塞"、"喷涌"和"结饼"等不良现象,进而影响施工进度。本文以北京市通州区畅和西路(兆善大街-潞阳大街)大断面矩形顶管施工为工程依托,开展了掌子面渣土改良试验研究。以不同配比的钠基膨润土、聚丙烯酰胺(PAM)和水作为砂土改良的添加剂,并通过黏度试验和滤失试验对不同配比的改良剂(膨润土添加聚丙烯酰胺)的性能进行了研究,结合改良后渣土的坍落度试验、直剪试验与压缩试验,评价了掌子面渣土的改良效果。研究表明:膨润土添加聚丙烯酰胺对无水砂层的改良效果显著。通过改良剂性能试验,初步筛选出膨润土∶PAM∶水为60︰2︰1000,70︰1.5︰1000,70︰2︰1000和80︰1.5︰1000等4种性能优良的改良剂配比;通过渣土改良效果试验得出,改良剂最优配比膨润土∶PAM∶水为70︰2︰1000,改良剂最优注入比为15%;通过添加改良剂使得改良后渣土的坍落度降低30 mm,黏聚力增加9.3 k Pa,内摩擦角降低6.5°,压缩系数增加0.090 MPa-1,达到了无水砂层土体处于流塑性状态的预期效果,有效降低了大断面矩形管廊侧壁阻力,提高了顶进效率。

During the construction of large rectangular cross-section pipe corridor in anhydrous sand layer,due to the poor flow plasticity of sand,the bad phenomena such as"blocking","gushing"and"cake forming"are easy to appear on the face of the pipe,which can affect the construction progress.This paper is based on the construction of rectangular pipe jacking with large section in Changhe West Road(Zhaoshan Street-Luyang Street),Tongzhou District,Beijing.It carries out the experimental study on the improvement of muck of front face.It uses different ratios of sodium base bentonite,polyacrylamide(PAM)and water as additives of sandy soil improvement.It uses viscosity test and filtration test of different ratios of modifying agent(bentonite added polyacrylamide)performance.It further uses the modified waste residue of the slump test,direct shear test and compression test,and evaluates the constraints of waste residue.The results show that the effect of adding polyacrylamide to bentonite on anhydrous sand is remarkable.According to the performance test of the improver,four good modifiers of bentonite∶PAM∶water:60︰2︰1000,70︰1.5︰1000,70︰2︰1000 and 80︰1.5︰1000 are screened.The results show that the optimal ratio of modifier bentonite∶PAM∶water is 70︰2︰1000,and the optimal injection ratio of modifier is 15%.By adding the modifier,the slump of the modified soil is reduced by 30 mm,the cohesion is increased by 9.3 kPa,the internal friction angle is reduced by 6.5°,and the compression coefficient is increased by 0.090 MPa-1.At this time,the anhydrous sand soil is close to the plastic-flow state,which effectively reduces the side wall resistance of large section rectangular pipe and improves the jacking efficiency.