玄武岩纤维加筋TRD防渗墙的抗水力劈裂性能

Splitting and tensile properties of basalt fiber reinforced cut-off wall by TRD

高渗压下帷幕防渗结构既要求有良好防渗性能,又要保证其抗剪与防止水力劈裂性能。利用TRD工法在水泥土搅拌方式上的突破,系统研究TRD施工中实现玄武岩纤维在水泥土中分散均匀的现场搅拌工艺,提出玄武岩纤维加筋TRD防渗墙的施工方法。对取芯后的试样开展劈裂抗拉强度试验,讨论水泥和玄武岩纤维掺量、玄武岩纤维长度、养护龄期等因素对玄武岩纤维加筋TRD防渗墙抗水力劈裂特性的影响。结果表明:对于搅拌分散液,P.O 42.5级普通硅酸盐水泥、钠基膨润土、玄武岩纤维与地层土体的搅拌效果较为理想;加筋水泥土的抗拉强度随着玄武岩纤维掺量和长度的增加会出现先升高后降低的峰值特性,最优玄武岩纤维掺量和长度分别为0.4%和12mm。

The curtain anti-seepage structure requires both good anti-seepage performance,as well as anti-shear and hydraulic splitting resistance under high osmotic pressure,which prevents the risk of hydraulic fracturing damage inside the anti-seepage layer.In the construction of traditional cement-soil mixing piles,the fibers are directly mixed with cement slurry.The fibers generally agglomerate and float on the surface of the slurry or settle down,so it is difficult to achieve uniform dispersion.Simultaneously,the biaxial or triaxial cement-soil mixing pile is mainly mixed horizontally inside a single soil layer,and the fibers will be concentrated in the local depth of the cement-soil cut-off wall,which makes it difficult to guarantee the overall quality of the cutoff wall.In the construction site,the direct mixing method to mix basalt fiber and cement soil can not meet the uniformity requirements.Basalt fiber concentration will occur at the bottom or part of the wall,which can easily block the slurry outlet of the TRD host.The basalt fiber was selected as a reinforcing material to improve the tensile strength of cement soil,and the measurement was conducted on splitting and tensile properties of basalt fiber reinforced cut-off wall by TRD.Selection of an external admixture to make the fiber bundles became monofilaments and disperse in the cement slurry.Through the mixing dispersion test,the mixing effects of yellow sand,gypsum powder,plain fill,and sodium bentonite as dispersing mixing materials were studied respectively,and the results were obtained.The basalt fiber reinforced TRD anti-seepage wall construction mixing dispersion material was based on the composition of mass parts,so the on-site mixing process was systematically studied to achieve uniform dispersion of basalt fiber in cement soil during TRD construction and proposes basalt fiber addition construction method of reinforced TRD cut-off wall.The basalt fiber reinforced TRD cut-off wall was drilled and sampled by the open thin-wall soil extractor,and the core sample preparation was carried out by the thin-walled bulldozing and ring knife sample method.The size of the prepared sample was50 mm×100 mm.The split tensile strength test was carried out on the cored sample,and the obtained tensile strength was converted by applying the linear elastic theory.Then,the influence of cement and basalt fiber content,basalt fiber length,curing age,and other factors on the hydraulic fracturing characteristics of basalt fiber reinforced TRD cut-off wall were also discussed.The experimental results indicated that the composition of the construction mixing dispersion material in parts by mass was:P.O 42.5 grade ordinary Portland cement,with the mixing amount wass 25%and water-cement ratio of 1.3.The sodiumbased bentonite,with a mixing amount of 100 kg/m3 and water-cement ratio of 18.6,and basalt fiber,which mixing amount was0.4%,respectively.When curing for 28 d,0.4%of basalt fiber added to the cement-soil sample can obtain a tensile strength growth rate of 50.0%.The tensile strength of reinforced cement soil increased first and then decreased due to the increased basalt fiber content and length.The optimal basalt fiber was 12 mm long with the content of 0.4%.The proposed basalt fiber reinforcement technology can make the basalt fiber monofilament evenly distributed in the cement soil,and the final dispersion has a moderate consistency to facilitate mechanical mixing with the soil.Adding basalt fiber to cement soil can effectively increase the tensile strength within a certain range,and can effectively improve the hydraulic splitting resistance of the cement soil impervious wall.As the curing age increases,the tensile strength of the sample also increases.