Experimental study on expansion deformation of non-thermal-bonding composite geomembrane under ring restraint
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摘要: 由于热融合工艺在复合土工膜生产和施工分体拼接过程中,容易灼伤土工膜而产生隐患,因此在南水北调东线大屯水库全库盘防渗中采用了膜、布单独铺设的分离式复合土工膜。针对分离式复合土工膜的气胀问题,将其变形简化为环向约束条件下的球形鼓胀变形并进行了胀破试验,结论如下：①分离式复合土工膜（膜0.4 mm,布250 g/m2）鼓胀变形的胀破压力随加载速率（用液体压入速率示）的增加而缓慢增大,基本加载速率推荐采用100 mL/min。②其鼓胀变形张应力–应变关系曲线可分为线性、塑性、强化和胀破4个阶段,曲线整体形态与土工布类似；其中线、塑性阶段时间很短,曲线形态与膜类似,受膜影响较大；强化阶段时间长,曲线形态与布类似,主要要受土工布影响。③其鼓胀压力由膜、布共同决定,变形初期土工膜承担较多内压力,影响较大；之后土工布逐渐承担越来越多的内压力,并起决定作用,直到发生破坏,相应胀破压力为1.51 MPa,胀破冠顶高度31.5 mm。④其鼓胀变形破坏的断裂伸长率为25.3%,主要由土工布的断裂伸长率决定；破坏形态分为不完全破坏和完全破坏,其原因分别为土工布的非均匀和均匀变形。Abstract: The non-thermal-bonding composite geomembrane separately laid by geomembrane and geotextile is adopted in the horizontal anti-seepage control schemes of Datun Reservoir on the Eastern Route of the South-to-North Water Diversion Project. The reason is that the heat-melt craft is easy to burn the composite geomembrane in the process of production and welding construction, and then to cause hidden troubles. The mechanical model for the air expansion deformation of the non-thermal-bonding composite geomembrane is simplified to the spherical bulging deformation under the ring restraint, and the experiment is accomplished. The conclusions are drawn as follows: (1) The bursting pressure of the non-thermal-bonding composite geomembrane (the thickness of geomembrane is 0.4 mm, the mass per unit area of geotextile is 250 g/m2) increases slowly with the increase of loading rate. The basic loading rate, i.e., liquid injection rate, is recommended to be 100 mL/min. (2) The unit tensile force and strain curve can be divided into four stages: linear, yield, strengthening and bursting. Its overall shape is similar to that of geotextile. The curve shape is similar to that of the geomembrane, which has greater influence during the very short linear and yield stages. In the strengthening stage, the curve shape is more like that of the geotextile and is mainly determined by the geotextile. (3) The expansion and bursting pressure is determined by both the geomembrane and the geotextile. In the initial stage of the deformation, the geomembrane bears more internal pressure. Then the geotextile gradually bears more and more internal pressure and plays a decisive role until failure. The bursting pressure is 1.51 MPa, and the bursting height is 31.5 mm. (4) The elongation at break of expansion is 25.3%, which is mainly determined by the geotextile. There are two types of failure patterns: incomplete failure and complete failure, caused respectively by the non-uniform deformation and uniform deformation of the geotextile.
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图 5 分离式复合土工膜不完全/完全破坏形态
Figure 5. Incomplete/complete failure patterns of non-thermal-bonding composite geomembrane samples
表 1 试验材料常规试验指标
Table 1 Routine test indexes of composite geomembrane
类型 厚度/mm 密度/(g·cm-3) 单位面积质量/(g·m-2) 断裂强度/(kN·m-1) 断裂伸长率/% 聚乙烯土工膜 0.4 0.926 — 8.1 615.0 短纤针刺无纺布 — — 250 8.2 62.7 
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表 2 分离式复合土工膜破坏形式统计表
Table 2 Failure patterns of non-thermal-bonding composite geomembrane samples
序号 加载速率/(mL·min-1) 胀破压力/MPa 破坏形式/次 不完全破坏 完全破坏 1 80 1.44 2 4 2 90 1.47 3 3 3 100 1.51 4 2 4 110 1.52 1 5 5 120 1.53 4 2 6 130 1.52 3 3 合计 17 19
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