Preparations Before Construction
Material Preparation: According to the design requirements of the reservoir, select geomembranes with appropriate specifications and quality, such as high-density polyethylene geomembranes, etc., and prepare corresponding welding materials, anchoring materials, etc. The common thickness of geomembranes is between 0.5mm and 2.0mm, and the width of each roll is generally 4m to 6m.
Site Clearance: Remove debris, stones, branches and other sharp objects, as well as the surface humus soil in the construction area of the reservoir, to ensure that the surface of the foundation is flat, solid, and has no obvious unevenness or cracks.
Foundation Treatment: Compact and level the foundation to make it reach the required density and slope in the design. For foundations with soft soil layers or uneven settlement, special treatments such as replacement and reinforcement may be required.
Laying of Geomembrane
Laying Sequence: Generally, the laying shall be carried out in the order from bottom to top and from inside to outside. First, lay the geomembrane on the bottom of the reservoir, and then lay the geomembrane on the reservoir walls.
Laying Method: Use the manual rolling and laying method. Unroll the geomembrane roll on an open space, cut it into the required shape according to the predetermined plan, and then lay it smoothly and tightly on the foundation, minimizing wrinkles as much as possible. The overlapping width between adjacent geomembranes is generally 10cm to 20cm, which is determined according to the specific type of geomembrane and design requirements, and ensure that the overlapping part is flat and tight.
Reserved Expansion Amount: Considering that the geomembrane may expand or contract due to factors such as temperature changes and foundation deformation during use, a 1% - 4% expansion allowance should be reserved during laying to prevent the geomembrane from being torn.
Geomembrane Welding
Welding Methods: Commonly used welding methods include hot-melt welding and extrusion welding. Hot-melt welding is suitable for thicker geomembranes. By heating the edges of the geomembranes to make them melt, and then connecting two pieces of geomembranes together under certain pressure; extrusion welding is to heat and extrude the welding rod and fill it at the seams of the geomembranes to form a sealed weld.
Welding Equipment: Use professional geomembrane welding machines for welding operations. Before welding, check whether the performance of the equipment is normal to ensure that parameters such as welding temperature, speed and pressure meet the requirements of the welding process.
Welding Quality Control: During welding, ensure the continuity and tightness of the welds, and avoid defects such as missed welding, false welding and skip welding. The welds should be flat, firm and have a uniform width, generally not less than 10mm. After welding is completed, the welds should be inspected in a timely manner. For example, use the visual inspection method to check whether there are defects such as bubbles, slag inclusions and melting points on the appearance of the welds, or use methods such as the inflation method and the vacuum method to test the tightness of the welds.
Anchoring and Fixing
Anchoring Trench Setting: Excavate anchoring trenches around the reservoir. The depth of the trench is generally 30cm to 50cm, and the width is about 40cm. Put the edges of the geomembrane into the anchoring trench, and backfill with soil and compact it to fix the position of the geomembrane and prevent it from displacing during use.
Fixing Methods: In addition to fixing with the anchoring trench, materials such as U-shaped nails and steel wires can also be used to assist in fixing the geomembrane. Especially at the overlapping parts and corners of the geomembrane where displacement is likely to occur, strengthen the fixation to ensure the stability of the geomembrane.
Construction of Protective Layer
Fine Sand Protective Layer: After the geomembrane is laid, the fine sand protective layer should be laid in a timely manner to protect the geomembrane from being damaged by external factors. The quality of the fine sand should meet the requirements, with a mud content of no more than 5% and good gradation. The laying thickness is generally about 30cm, which can be laid in layers, with each layer having a thickness of not less than 10cm, and compacted with tools such as wooden boards.
Other Protective Layers: According to needs, a layer of rubble, precast concrete blocks or plain concrete can also be laid on the fine sand protective layer as a further protective layer to enhance the protection of the geomembrane and prevent it from being damaged by water flow scouring, heavy object extrusion, etc.
Construction Quality Inspection and Acceptance
Appearance Inspection: Check whether the surface of the geomembrane is flat, and whether there are defects such as wrinkles, damages and holes; check whether the appearance of the welds meets the requirements and whether there are problems such as missed welding, false welding and bubbles.
Dimension Inspection: Check whether the laying position, overlapping width and anchoring length of the geomembrane meet the design requirements.
Weld Detection: Use methods such as the inflation method, the vacuum method or the tensile test to detect the welds to ensure that the tightness and strength of the welds meet the design requirements.
Acceptance Standard: According to the relevant construction quality acceptance specifications and design requirements, conduct a comprehensive acceptance of the construction quality of the geomembrane reservoir. It can be put into use only after passing the acceptance.
