Comprehensive building materials for construction engineering are a new class of geotechnical construction building materials. It is a general term for all products produced from raw materials such as synthetic fibers, resins and synthetic rubbers. It is used inside engineering materials, on the surface and inside various structures, playing the function of strengthening or protecting structures. The basic materials for construction engineering are an interdisciplinary product that gradually emerged with the development of petrochemical processes and textile engineering technology. Composite geomembranes are now widely used in anti-seepage construction of plain hydropower stations. New dams built using the method of cement membrane roof leakage, such as the Heitu Dike in Liaoning, but there are also dangerous earth-rock dams protected with cement membranes, such as the earth-rock dam of Yuankou Hydropower Station in Zhejiang Province, the earth dike of Lijiaqing Hydropower Station in Yunnan, etc.
Geomembranes without cracks have very low permeability, especially under conditions of small water head, their permeability is close to zero. The main factors causing defect leakage are damage during construction, insecure connection welds with concrete membranes, damage during handling, and damage to construction tools during laying, etc. The lower backing plate of composite geomembrane is usually filled with coarse-grained soil such as gravel with larger particle size, non-smooth surface and large gaps. The protruding coarse particles will locally jack up the composite geomembrane as a whole. Under the influence of huge water head, the jacked-up part of the composite geomembrane will suffer huge tension and produce changes or rupture to produce gaps. Under the continuous influence of ultra-high huge pressure water head, the gaps will gradually expand, and the gap thickness will also gradually increase. When the composite geomembrane ruptures to a certain extent, gap leakage leads to an increase in linear seepage in the earth-rock dam, which may cause serious safety accidents. The composite geotechnical layer may also be damaged due to gas expansion. Gas will be supported on the concrete layer, causing gas expansion damage to the concrete layer. Moreover, when the water head drops too much, the gas pressure supported by the gas is much larger than the normal water head pressure, which will cause gas-liquid expansion damage. The mechanical characteristics of composite geomembrane have both the characteristics of geotextile and the characteristics of concrete membrane. Due to the role of geotextile, its mechanical characteristics have been greatly improved compared with pure concrete membrane, and its tensile strength, top-breaking resistance, and puncture resistance are all greatly enhanced.
In addition, the stress-strain curve of composite geomembrane is still the same as geotextile when geotextile ruptures. After geotextile ruptures, due to the strong extensibility of geomembrane material, it is the same as the stress-strain curve direction of pure concrete membrane during continuous tensile deformation. However, the thickness and strength of geomembrane are not directly related to the waterproof leakage of composite geomembrane. What affects its waterproof leakage is the shape of the concrete membrane and the relative deformability of the composite geomembrane. Of course, the degree of compaction between the geotextile and concrete layer in the composite geomembrane also plays an important role in its thermodynamic properties. According to experimental observations, the degree of bonding has a greater effect on its tensile strength, while the top-breaking force is small. Therefore, in the product design of composite geomembrane, the tensile strength of geotextile must be listed as a key product design goal, while the tensile strength of a single concrete layer can become a safety reserve. The durability of composite geomembrane is one of the key items among its advantages. And the key factors directly affecting its durability are aging and creep. The aging of composite geomembrane is generally due to heat, light, oxygen, chemical conditions and stress intensity, etc. The creep of concrete film refers to the current situation where its stress level is constant, and the deformation area gradually increases with the increase of duration. The magnitude of creep resistance generally depends on the chemical characteristics of raw materials and production processes.
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