Construction process of HDPE Geosynthetic Membrane for Landfill Project
1. Construction preparation for landfill site (construction of impervious HDPE geomembrane liner). After leveling the bottom of the landfill site, according to the design requirements, the underground water collection pipe trench is manually excavated, the remaining soil is transported to the surrounding area of the reservoir bottom, the anti-seepage material is laid from bottom to top, the gravel groundwater diversion layer membrane material and the upper and lower layer geotextile are laid. After the inspection, the prepared pebble stones are paved with machinery and manual. The concrete operation is as follows: the plastic film and the upper layer geotextile of the reservoir dam shall be laid first. After the plastic film and the upper layer geotextile are laid and accepted, one excavator shall be arranged at the bottom and top of the dam respectively to transport the pebble diversion layer to the reservoir dam slope, and then level it manually. In order to ensure the laying quality, membrane material laying and diversion layer should be carried out equally and constructed in different areas. The construction sequence of landfill site leveling is to clear the slope first, and then level the bottom of the reservoir; the principle of slope leveling is to save earthwork, first remove the surface soil within the scope of the reservoir bottom during leveling, and pile it in the covering soil preparation yard as daily covering soil.
2. Construction Process Flow. Plane compaction of reservoir bottom — 30cm thick pebble groundwater diversion layer — laying filament geotextile (200g / m2) — paving 30cm thick clay layer — paving bentonite cushion 4800G / m2 — 2mm thick HDPE film — joint welding — laying filament geotextile (600g / m2) — 2cm thick medium coarse sand layer — filament geotextile (200g / M2) — 30cm thick pebble leachate diversion layer — filament geotextile 200g / m2 ）- primary waste.
3. Quality inspection of HDPE Geosynthetic Membrane Liner and geotextile materials. The anti-seepage membrane and geotextile used in the project are two cloth and one membrane and one cloth and one membrane needling anti-seepage membrane and geotextile. Before use, the laboratory is entrusted to test the technical indexes of the products, and all indexes meet the standard requirements and design requirements.
The impermeable geosynthetic membrane and geotextile have certain anti bursting and anti piercing ability, but in the process of filling garbage, the gravel under the film and the root are often broken. In the anti-seepage construction of the landfill site, the earth excavation shall be removed to the clay layer, and the slope shall be cut and leveled according to the design size, and the underslope shall be backfilled and compacted, leveled and watered for compaction, so that the dry bulk density of the compacted fill shall not be less than 1.65t/m3. The hard sharp objects such as stones and tree roots on the surface shall be removed, and herbicides and other chemicals shall be sprayed. The finished slope surface shall be flat, dense and smooth to prevent the impervious membrane and geotextile from being punctured. After meeting the requirements of design flatness, it is accepted by the supervision engineer to provide working face for the laying of anti-seepage membrane and geotextile.
4. Laying method of HDPE geomembrane and geotextile. The anti-seepage membrane and geotextile are laid at the bottom of the reservoir and laid on the slope. Laying method: the impervious membrane and geotextile are required to be spliced and welded into 20m width on the flat ground, and then laid on the slope surface from top to bottom and perpendicular to the dam axis. After the slope surface is laid and accepted, it is slowly spread from the top of the embankment to the toe of the dike along the direction perpendicular to the embankment axis to connect with the geomembrane at the bottom of the reservoir at the top of the tooth groove at the foot of the slope. After the excavation and acceptance of the bottom of the reservoir is qualified, the bottom of the reservoir shall be slowly paved from the top of the tooth groove to the inside of the reservoir along the direction perpendicular to the axis of the dike foot to the place 25m inside the reservoir.
The laying shall be carried out in dry and warm weather. In order to facilitate splicing and prevent stress concentration, the anti-seepage membrane and geotextile shall be laid in wave form with a margin of about 1.5%. After spreading, the anti-seepage membrane and geotextile shall be leveled and pulled out in time. It is required that the anti-seepage membrane and geotextile shall be consistent with the slope surface without protrusion and wrinkle. The construction personnel shall wear flat bottom cloth shoes or soft rubber shoes, and shall not wear nail shoes to avoid stepping on the geomembrane, If the geomembrane is damaged during construction, it shall be repaired in time.
5. Splicing of HDPE geomembrane and geotextile. The project adopts two cloth and one membrane and one cloth and one membrane for seepage control. The connection of anti-seepage membrane and geotextile is divided into two procedures, i.e. joint of upper layer geotextile and connection of lower layer HDPE membrane. The joint of geotextile is carried out by hand-held sewing machine and nylon thread, the lap width is 10cm; HDPE film is connected by welding process, and the welding tool is double channel plastic heat sealing machine with automatic temperature regulation (speed regulation) electric heating mode. Splicing includes the joint of geotextile and the welding of geosynthetic membrane. In order to ensure the welding quality, welding should be carried out in the factory as far as possible. However, for the convenience of construction, the width of anti-seepage membrane and geotextile should not be too wide, so they must be spliced at the construction site.
The quality of anti-seepage membrane welding is the key to the success or failure of anti-seepage performance. Therefore, the welding of geomembrane must be done well to ensure the welding quality. Therefore, the manufacturer should send professional and technical personnel to the site for operation, guidance and training, and use special welding equipment for geosynthetic membrane. The geomembrane of the project is welded by a professional thermal sealing geomembrane welding machine, and the geotextile is welded by a portable packer.
Welding process: after the first geomembrane is laid, the side to be welded shall be overlapped (about 60cm wide), and the second sheet shall be laid on the first membrane in reverse. The welding edge direction of the two geomembranes shall be adjusted to overlap 10cm.
All welding shall be carried out on site. It is required that the weather is fine and the wind force is below grade 3. It is strictly forbidden to carry out construction in rainy days, high temperature and severe cold weather. The surface of welding base shall be dry. Before welding, the sand, soil and other dirt on the membrane surface shall be blown off with an electric blower, and then cleaned with a clean towel to ensure that the membrane surface is clean. A long board is placed under the welding part to facilitate the welder to walk on the flat base surface Before formal welding, HDPE film of the same material shall be used for trial welding according to the construction temperature and HDPE film thickness. The welding temperature shall be 220-300 ℃, and the welding machine temperature and walking speed shall be mastered, and the construction process parameters shall be determined before formal construction. The weld shall be transparent, smooth, straight and continuous. Two welding seams are spliced, each of which is 10 mm wide. A cavity of 10 mm is reserved between the two welds. The quality of the weld is checked with this cavity.
6. Anchoring of HDPE geosynthetic membrane and geotextile. The anchoring of anti-seepage membrane and geotextile is divided into the anchoring of dam slope and the anchoring of reservoir bottom. The upper anchoring is to embed enough anti-seepage membrane and geotextile at the bottom of the embankment foundation on the top of the dam. Its structural form is rectangular groove, and the filling is rammed in the groove. The trench shall be excavated along the design line of the dam toe. When the anti-seepage membrane and geotextile are laid, the anti-seepage membrane and geotextile shall be close to the inside of the trench, and the filling shall be tamped in the trench.
7. Precautions. In the area close to the level, the formation of bulge is prevented. The bulge will concentrate the gas from the soil under the plastic film layer, so it is necessary to consider the gas discharge outward or at the top. The number of construction joints, especially the horizontal joints on the dam slope, should be reduced as much as possible.
The HDPE geosynthetic membrane shall be protected from perforation during the laying of protective layer. Vehicles and hard soled shoes are strictly prohibited to walk on the HDPE geomembrane liner. Special treatment should be taken at the contact part between the plastic film and the buildings on the top of the dam body and the rigid body under the design water level to avoid leakage and ensure the safety of the landfill area of the refuse plant.
The laying strength of daily construction should be well controlled. The anti-seepage membrane and geotextile laid on the same day must be covered on the same day, and it is not allowed to be exposed for a long time, resulting in material aging.