Experimental study on air expansion deformation of geomembrane under ring-restrained conditions
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摘要: 对于库底采用土工膜水平防渗的围坝型平原水库,由于库水渗漏、地下水位上升等多种原因,使库区非饱和土层中孔隙气体聚集、上升,并在土工膜膜下形成有压气体,使土工膜产生局部隆起的气胀现象。根据土工膜气胀鼓起变形的特点,将土工膜气胀变形近似简化为环向约束球形鼓胀变形。为了解土工膜环向约束条件下球形鼓胀变形的特性,研制了4种不同规格的土工膜气胀变形专用试验设备,分析了试验设备孔径对土工膜胀破压力的影响,选择外径20 cm试验设备作为土工膜气胀变形试验的基本设备。利用选定的土工膜气胀变形基本试验设备,进行了环向约束条件下土工膜气胀变形和气胀破坏试验,总结了土工膜气胀变形和破坏的规律,得出结论：①土工膜气胀应力应变曲线可分为线性变形、强化变形、弱化变形和胀破拉断4个阶段;②气胀变形表现为不均一性,气胀破坏为张拉破坏,破坏形态表现为一条通过球冠顶点的大圆曲线或不通过球冠顶点的小圆曲线;③对于厚度0.35~0.6 mm的土工膜,其气胀胀破压力为0.08~0.12 MPa,胀破冠顶高度为4.6~5.5 cm;④对于厚度0.35~0.6 mm的土工膜,其气胀延伸率为17.6%~18.5%,远小于土工膜单向拉伸延伸率。Abstract: For the surrounding dam plain reservoirs that use a horizontal anti-seepage scheme, the leakage of reservoir water, rise in groundwater table and other reasons lead to the pore gas in unsaturated soil under the geomembrane gather, rise and change into pressure, which can cause geomembrane air expansion with local swelling. According to its characteristics, the air expansion deformation of geomembrane is simplified as the spherical bulging deformation under ring-restrained conditions. A set of test equipment with four different diameters is developed to study the characteristics of air expansion deformation of geomembrane under ring-restrained conditions, and the influence of the diameter of test equipment on burst pressure of geomembrane is analyzed. The test equipment with outside diameter of 20 cm is selected as the basic equipment of air expansion of geomembrane. A test is conducted using the selected equipment, and the rules of air expansion deformation and failure of geomembrane are summarized. The conclusions are drawn as follows: (1) The stress-strain curves of air expansion deformation of geomembrane can be divided into four stages: linear deformation, strengthening deformation, weakening deformation and bursting break. (2) The air expansion deformation is not uniform, the mechanism of air expansion failure is the tension failure, and the failure mode is a great circle curve through the vertex of spherical cap or a small round curve which does not pass through the vertex of the spherical cap. (3) For the geomembrane with thickness of 0.35 ~ 0.6 mm, the burst pressure of air expansion is 0.08 ~ 0.12 MPa, and the air expansion crown height is 4.6 ~ 5.5 cm. (4) For the geomembrane wiht thickness of 0.35 ~ 0.6 mm, the air expansion elongation is 17.6% ~ 18.5%, which is far less than the unidirectional tensile elongation of geomembrane.
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