Geotechnical grille inspection items and methods

   Date:2020-04-20     Browse:15    
Core tips:Geogrid is made of polypropylene and high-density polyethylene as raw materials, which are made by special extrusion an
      Geogrid is made of polypropylene and high-density polyethylene as raw materials, which are made by special extrusion and bidirectional stretching. Can reduce the required structural fill, uniform load distribution, has a high bidirectional tensile modulus and tensile strength, high resistance to mechanical damage, durability. Mainly suitable for soft soil foundation treatment and reinforced soil structure.
      Geogrid is a main geosynthetic material. Compared with other geosynthetic materials, it has unique performance and efficacy. Geogrids are often used as reinforcement for reinforced earth structures or composite materials. Geogrid is a polymer mesh with a square or rectangular shape formed by stretching. It can be uniaxially stretched or bidirectionally stretched according to the direction of stretching during manufacture. It punches holes in the polymer sheet (mostly polypropylene or high-density polyethylene) made by extrusion, and then performs directional stretching under heating conditions. The uniaxially stretched grid is only stretched along the length of the sheet, while the bidirectionally stretched grid is made by continuously stretching the unidirectionally stretched grid in the direction perpendicular to its length.
       In the manufacture of geogrid, the polymer macromolecules will be rearranged and oriented with the heating and extension process, which strengthens the coupling force between the molecular chains and achieves the purpose of improving its strength. Its elongation is only 10% to 15% of the original sheet. If anti-aging materials such as carbon black are added to the geogrid, it can have good durability such as acid resistance, alkali resistance, corrosion resistance and aging resistance. Geogrid is made of high molecular polymer through extruding, forming and punching process, and then stretched vertically and horizontally. The material has great tensile strength in the longitudinal and transverse directions. This structure can also provide an ideal chain system for more effective force bearing and diffusion in the soil, suitable for large-area permanent bearing Foundation use: The geogrid is suitable for the reinforcement of various dams and subgrades, slope protection, hole wall reinforcement, large-scale airports, parking lots, dock yards and other permanently loaded foundations.
      Construction points: excavation foundation bed: setting sand cushion layer (height difference is not more than 10cm), rolling into a platform, laying grid, longitudinal axis should be consistent with the main force direction, longitudinal overlap 15-20cm, horizontal 10cm, The lap joints are tied with plastic tape, and the ground of the paved grid is fixed with U-shaped nails every time. The paved geogrid should be backfilled in time. The number of paved geogrid layers depends on the technical requirements.
      experiment method
      1. Sampling
      In the same batch of geogrid products, one roll is randomly selected, and the full width of 1M is taken as a sample.
       2. Appearance
       Visually inspect the product in natural light.
       3. Size deviation
       Flatten the geogrid to measure the width and calculate the deviation.
       4. Tensile strength test per linear meter
       Standard environment for sample condition adjustment and testing. The sample should be in an environment of (20 ± 2) ° C for at least 12 hours and tested in this environment.
       5. Equipment
       The equipment is a tensile testing machine with a reading accuracy of 10% to 90% of the measuring range.
       6. Sample Preparation
When the geogrid is tested by the single rib method, after removing the two ribs on both sides of the sample when cutting the sample, 10 samples are uniformly cut in the width direction. The length of the sample includes at least two complete units, and the length is not less than 250mm.
       Geogrid inspection project
       ① Tensile strength: In the tensile test, the large tensile stress that the sample receives until it is broken is the tensile strength, which is called tensile strength in academia.
       ② Elongation: Elongation is the percentage of the ratio of the total deformation of the gauge segment after the tensile fracture of the specimen to the original gauge length.
       ③ Tear strength: it is a term defined in a test method for determining the tear resistance of a film or sheet. This method is a tear test performed on a special test machine by cutting a sample with a prescribed crack.
       ④ Bursting strength
       ⑤ Thickness
       ⑥ Mass per unit area
       ⑦ Permeability coefficient: Permeability coefficient is also called hydraulic conductivity coefficient. In an isotropic medium, it is defined as the unit flow rate under a unit hydraulic gradient, indicating the difficulty of the fluid passing through the pore skeleton.
       In addition, the geogrid inspection also includes appearance, physical properties (including: unit area mass measurement, amplitude measurement, mesh size measurement); mechanical properties (including: strip tensile test, joint / seam wide strip tensile test, Sticky solder joint) item inspection.
 
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