Construction preparation

Compared with other synthetic materials, the laying of geomembrane is more complicated. First of all, the various indicators of the geomembrane (density, tensile strength, elongation and tear strength, etc.) must be tested on site, and then site treatment, membrane joint welding, defect repair, destructive testing, and backfill protection must be carried out.

First clean the slope, and then level the bottom of the field area; the principle of leveling the side slope: save the amount of earthwork. When leveling, first remove the surface saline soil including the bottom of the field area, and pile it in the cover soil preparation yard as the daily cover soil; then follow the The elevation and coordinates of each control point will level the bottom of the site into a site with a vertical slope of 1.2% and a horizontal slope of 1.2%.

1. Quality inspection of geomembrane and geotextile materials. Check the technical indicators of the product before use, and all indicators must meet the standard regulations and design requirements before use.

2. Geomembrane and geotextile have certain resistance to burst and puncture, but in the process of filling garbage, they are often burst by sharp gravel and branches under the membrane. During the construction of the geomembrane in the landfill, the earthwork is excavated and removed to the clay layer, and the slope is cut and excavated according to the design size, and the underslope is backfilled and compacted. And remove the hard sharp objects such as stones and tree roots on the surface, and spray herbicides and other medicines. The slope after finishing should be flat, closed, and smooth to prevent the geomembrane and geotextile from being punctured. After reaching the design flatness requirements, the supervising engineer will accept and pass the inspection, and provide a working surface for the laying of geomembrane and geotextile.

3. Geomembrane splicing in the field. In order to facilitate construction and ensure the quality of splicing, the geomembrane and geotextile should be as wide as possible to reduce the amount of splicing on the dam slope. layout.

2 Laying of geomembrane and geotextile

2.1 Laying method of geomembrane and geotextile

Geomembrane and geotextile laying are divided into two parts: bottom laying and slope laying. Laying method: The laying of geomembrane and geotextile requires that the auxiliary width be spliced ​​and welded to a width of 20m on the flat ground, and then laid from top to bottom on the slope, perpendicular to the direction of the dam axis. After the slope is laid and passed the acceptance of the slope, it is slowly spread from the top of the embankment to the toe of the embankment in the direction perpendicular to the axis of the dam to the outer top of the groove of the toe of the slope to connect with the geomembrane at the bottom of the field in a T-shape. The bottom of the field area is laid after the excavation and acceptance of the bottom of the field area is qualified, and it is slowly spread from the outer top of the tooth groove to the inside of the silo along the direction perpendicular to the axis of the embankment toe to 25m inside the silo.

2.2 Technical requirements for laying geomembrane and geotextile

The laying should be carried out in dry and warm weather. In order to facilitate splicing and prevent stress concentration, the laying of geomembrane and geotextile adopts wave-shaped relaxation method with a margin of about 1.5%. It is in line with the slope surface and has no protruding folds. The construction personnel should wear flat cloth shoes or soft rubber shoes. Boat spikes are strictly prohibited to avoid stepping on the geomembrane. If the geomembrane is damaged during construction, it should be repaired in time.

2.3 Splicing of geomembrane and geotextile

1. This project adopts one mesh, one cloth and one membrane to prevent seepage. The connection of geomembrane, geotextile and three-dimensional composite drainage network is carried out in three procedures, namely, the upper three-dimensional composite drainage network, the seam of the second layer of geotextile, and the lower HDPE membrane. Connection. The geotextile and the three-dimensional composite drainage net are sewn by using a portable sewing machine (sewing machine) and nylon thread for double-pass sewing. The lap width is 10cm; the HDPE film is connected by welding process, and the welding tool adopts automatic temperature regulation (speed regulation) electric heating mode double-channel plastic heat sealing machine. Splicing includes the seam of geotextile and the welding of geomembrane. In order to ensure the welding quality, the welding should be carried out on site as much as possible. However, for the convenience of construction, the width of geomembrane and geotextile should not be too wide, and must be spliced ​​at the construction site.

(1) The quality of the geomembrane welding is the key to the success or failure of the anti-seepage performance, so it is necessary to do a good job in the welding of the geomembrane to ensure the welding quality. Therefore, the manufacturer sends professional technicians to the site for operation, guidance and training. , using special welding equipment for geomembrane. The geomembrane welding of this project adopts a professional heat-bonding geomembrane welding machine, and the geotextile is seamed by a portable sealing machine.

(2) Welding process: After the first piece of geomembrane is laid, the sides to be welded are folded over (about 60cm wide), the second piece is laid on the first piece of film in reverse, and the direction of the welding edges of the two pieces of film is adjusted so that the The overlap is 10cm.

(3) Geomembrane bonding welding and testing

The bonding and welding of geomembrane is a key link in successfully preventing leakage. Usually the joint should be parallel to the slope (along the slope and as far as possible the horizontal joint should be placed at the bottom of the unit, ≥1.5m from the foot of the slope. There are two ways of geomembrane welding: fusion welding (double-track fusion welding), which requires membrane blocks Before welding, it must overlap by 10-15cm, and adjust the membrane block to reduce wrinkles, so that the two bent membrane blocks are welded together through the preset pressure gear; the other is hot-pressure corner welding (single seam welding). ), it requires the membrane block to overlap at least 7.5cm before welding, and then insert the molten resin electrode at the curved edge of the two layers of geomembrane, and use hot air to melt the material to make the surface of the thin layer evenly bonded. The completed geomembrane must be segmented according to design requirements Or divide into pieces for air pressure test (double-track fusion welding) and vacuum test (single-weld welding) and take samples of a certain length for destructive testing.

(3) All welding is carried out on site. The weather is required to be good, and the wind force is below level 3. It is strictly prohibited to perform construction in rainy days, high temperature and severe cold weather. Wait for the dirt, and then wipe it off with a clean towel to ensure that the film surface is clean. A long wooden board is placed under the welding part, so that the welding machine can walk on a flat base surface to ensure the welding quality. Before formal welding, it should be based on the construction temperature. , HDPE film thickness, use HDPE film of the same material for trial welding, the welding temperature is 22O ~ 300 ℃, master the welding machine temperature and walking speed, determine the construction process parameters, and then carry out the formal construction, the welding seam should be transparent and smooth. , straight, connect. Two splicing welds, each 10mm wide, leave a 10mm cavity between the two welds, use this cavity to check the quality of the welds.

2. Anchorage of geomembrane and geotextile

The anchorage of geomembrane and geotextile is divided into the anchorage of the dam slope and the anchorage of the bottom of the field area. The upper anchorage adopts the geomembrane and geotextile of sufficient length to be embedded at the bottom of the foundation of the dam crest to intercept the flood. concrete. The dam foot shall excavate a trench along the design line of the dam foot. When laying the geomembrane and geotextile, the geomembrane and geotextile shall be closely attached to the inner side of the trench, and the soil shall be rammed and filled in the trench. At the same time, the geomembrane and geotextile on the dam slope should be compacted and fixed with bagged soil from bottom to top, with a spacing of about 20 meters.

3 Construction quality control of geomembrane and geotextile

The laying of geomembrane and geotextile is the key to the construction of the project. Construction quality control includes material procurement, incoming raw material quality control, construction operation process control, and quality inspection after construction.

3.1 Material Procurement

Combined with the actual work and the specifications of the selected geomembrane and geotextile, determine the quality standards and geometric dimensions of the geomembrane and geotextile, and select a manufacturer with a larger production scale and product quality that meets the requirements for purchase.

3.2 Raw material quality control

The geomembrane and geotextile entering the site must have the certificate of conformity, performance and characteristic indicators and instruction manual provided by the manufacturer. After the geomembrane and geotextile enter the site, randomly select the geomembrane and geotextile for re-testing of their performance indicators, and the re-test results can be used only after they are all qualified.

3.3 Construction operation process control

Before laying the geomembrane and geotextile, weave the construction organization design, explain the laying method and technical measures, and use it after the approval of the supervisor. The construction personnel should wear flat shoes or soft rubber-soled shoes for laying. The geomembrane and geotextile should be laid in harmony with the laying of the protective layer and the laying of the diversion layer. In splicing, the quality of the geomembrane welding seam is the key to splicing. In the construction, the joint detection should be strengthened. The detection methods are: 1. Visual inspection method; 2. On-site leak detection.

Visual inspection method: After the geomembrane and geotextile are welded, observe whether there is any leakage, whether the seam is scalded, whether there are wrinkles, whether the splicing is even, etc.

On-site leak detection:

There are two types: A Inflation method: the welding seam is double strip, leaving a cavity of about 10mm between the two, seal both ends of the section to be measured, insert the gas needle, inflate to 0.05Mpa~ 0.20Mpa, and watch it for 0.5min , observe the vacuum gauge, if the air pressure does not drop, it means that there is no leakage, and the welded seam grid, otherwise it is necessary to find the cause and repair it in time.

B Water-filling method: The welding seam is double-striped, leaving a cavity of about 10mm between the two. Seal one end of the section to be measured, insert the water needle at the other end, and fill with water to 0.05Mpa~ 0.20Mpa. The leakage of the cavity indicates that the welded seam grid, otherwise the cause should be found and repaired in time.

The water filling method has the following advantages over the air filling method:

a Good intuition, easy to find problems in time:

b The equipment is simple, the operation is simple, and the spot check can be checked anytime and anywhere on the site. In view of the above advantages, this project adopts the water filling method to check the quality of the welds. For the certification visa section by section, repair welding should be carried out in time for the joints of virtual welding and missing welding, and the water filling test should be carried out for the repaired welding parts, and the next process can not be carried out until the acceptance is qualified.

3.3 Notes

1. In an area close to the level, prevent the formation of a bulge, which will concentrate the gas from the soil under the plastic film layer, so it must be considered that the gas is discharged outwards or at the top.

2. Minimize the number of construction joints, especially the horizontal joints on the dam slope.

3. Prevent the plastic film from being damaged by perforation during the laying of the protective layer. It is strictly forbidden for on-site vehicles and hard-soled shoes to walk on the plastic film.

4. The contact parts between the plastic film and the building on the top of the dam body and the rigid body under the design water level should be specially treated to avoid leakage and ensure the safety of the landfill area of ​​the garbage plant.

5. Control the strength of daily construction and laying. The anti-seepage membrane and geotextile laid on the same day must be covered on the same day, and must not be exposed for a long time, which will cause material aging.

3.5 Analysis of key and difficult processes in the implementation of this project and special solutions

1. Establish a system engineering system with anti-seepage as the core.

The most expensive part of artificial horizontal anti-seepage construction is civil engineering, but the core of the project is the anti-seepage project. Therefore, the entire project needs to establish a systematic engineering system for HDPE membrane construction. The foundation of civil engineering should meet the conditions of laying geomembrane, and the protective layer of non-woven geotextile should play a protective role. Only in this way can losses and waste be reduced, high-quality projects can be achieved, and overall effects can be achieved.

2. Carefully choose a geomembrane construction company.

The construction of geomembrane is the core of the whole project. The anti-seepage project of the landfill is a hidden project and irreversible. It can only be successfully constructed at one time. The one-time construction mentioned here means that construction quality is not required before being put into use. Qualified, the leakage is found to be irreparable after use. Therefore, it is necessary to choose a construction enterprise with strength, rich construction experience and good reputation, and the enterprise should have a well-trained construction team with stable personnel. The construction team of HDPE membrane is basically unfamiliar to the owners of the landfill site for the first time, and even the supervision unit is the first contact, and the construction quality largely depends on the construction company. The anti-seepage quality requires that the quality of each weld must be 100% qualified, which requires the construction company to conduct construction in accordance with its own standard construction and acceptance procedures when laying and installing. So what is the guarantee of construction quality? It depends on a series of technology, quality and complete original supervision data of on-site construction of the construction enterprise. Only under the supervision of a complete management system can we achieve qualified high-quality engineering quality.

3. How to deal with thermal expansion and contraction of materials caused by temperature changes during construction.

When the temperature difference of HDPE film is large, the phenomenon of thermal expansion and contraction is more serious. For example, the thermal expansion phenomenon is very obvious at noon due to the high temperature, and it mostly occurs at the foot of the slope or irregular places. Laying has a greater impact. The correct operation method should be to fully grasp the changing law of local temperature and avoid laying at high temperature at noon. For example, when laying in high temperature weather, the expansion and contraction amount within the maximum temperature difference should be calculated according to the thermal expansion coefficient of the HDPE film, and then sufficient length should be reserved during laying to adapt to the change of temperature difference.

  Summarize:

Landfills are currently an important method of garbage disposal in my country. Environmentally friendly landfills with HDPE anti-seepage treatment have been widely used across the country. During the construction, the current national construction specifications, operating procedures, process standards, construction acceptance and quality inspection acceptance standards shall be strictly implemented, so that the project can meet the qualified standards.