Comparison of Reinforcement Mechanisms of Geocell, Geogrid and Geotextile
In the 1960s, French engineer H.Vidal boldly used galvanized steel strips as reinforcement materials in the design of retaining walls and achieved good results. Later, he published many research papers on reinforced soil, and rented out the extensive application of reinforced geotechnical technology in retaining walls, roadbeds, slopes and foundations. development laid the foundation. Due to the excellent engineering properties and low cost of reinforced soil structures, it has been rapidly popularized and used all over the world. With the development of geosynthetics, the reinforced material has initially changed from metal sheet to two-layered geosynthetics made of polyethylene and polypropylene as the main raw materials. The continuous emergence of advanced manufacturing processes has continuously improved the strength, deformation resistance and anti-aging capabilities of geosynthetics, making geosynthetics widely used in civil engineering, water conservancy, transportation, railway and environmental engineering.
1 Structure comparison
Geocell is a new type of geosynthetic material developed in the 1980s. It is made of high-density polyethylene broadband by ultrasonic welding or anchoring and has a honeycomb cell structure. grid. The geogrid is a high-strength planar mesh material formed by directional stretching of high molecular polymer materials. If the height of the geocell is set to 0, the geocell is similar in shape to the flat geotextile, geonet, and geogrid. At this time, the three-dimensional structure of the geocell becomes a two-dimensional plane network structure, and the constraining and compacting effect between the reinforcement and soil becomes the effect of plane friction. It can be considered that flat geotextiles, nets and grids can be regarded as a special application form of geocells. Because the geocell has a certain height (above 5cm), the polymer sheet material is thick (above 1cm), the strength and modulus are large, and the welding strength is high, and the fillers filled in it together form a plate with high rigidity. The structure has a certain bending resistance, thereby dispersing the lateral stress of the upper structure.
2 Comparison of working principles
The reinforcement of geogrid is to use the tensile properties of the reinforcement to generate stress transmission through the frictional engagement with the surrounding soil interface, change the stress-strain field in the soil, increase the strength and toughness of the soil, and thus improve the deformation performance of the filler. , to improve soil stability. The rough surface and embedded solidity of the reinforcement are the main conditions for exerting the interfacial performance with the soil. The thickness of the nodes of the geogrid is greater than the thickness of the ribs, which can tightly connect the base of the coarse-grained soil together to form an interlocking structure. Or the interface effect in the opposite direction and the high stress transfer effect. The mesh is subjected to tensile load, so that the interlocking soil is subjected to compression and wrapping, thereby forming a stable bearing structure with a certain modulus.
2.21 Raft foundation effect and stress diffusion effect
As a three-dimensional reinforced material, the geocell interacts with the filler in the cell and works together to form a composite whole with considerable flexural, tensile and shear strengths. In engineering, this composite can be regarded as a flexible raft foundation, which can make the foundation damage develop to the deep layer, thereby improving the bearing capacity of the foundation. Under the action of uniformly distributed loads of a certain length, the shallow soft soil of the foundation is directly sheared, forming an active zone at the base, and a plastic transition zone on both sides below the active zone, causing uplift failure on both sides of the foundation. , forming a passive damage zone. Due to the low shear strength of soft soils, the ultimate load value to reach this failure state is low. For the cell foundation, because the geocell cushion has a strong shear resistance and improves the stress state of the shallow soft soil, the shear failure of the foundation develops toward the deep layer and reaches the ultimate load required for the critical failure state. higher. Since the cushion filler adopts coarse aggregate with a large internal friction angle and a high degree of compaction, it can effectively diffuse the load of the upper embankment, reduce the additional stress of the lying soft soil layer under the action, and improve the stress state of the shallow soft soil. Uniform stress distribution, thereby reducing settlement and uneven settlement, to achieve the purpose of strengthening the soft foundation.
2.2.2 Net pocket effect
Under the action of the upper load, the geocell structure forms a concave surface under the action of external force. The downward force acting on the upper part of the concave surface is greater than the upward force on the lower part of the concave surface, and the unbalanced part is contacted by the cushion layer and the soil. The interfacial shear friction force generated by the surface is balanced, that is, the pocket effect. The existence of the net pocket effect further reduces the vertical load on the soft soil layer, increases the vertical load on both sides, and effectively changes the stress distribution. The vertical stress difference is reduced, thereby reducing uneven settlement.
2.2.3 Double-sided friction
The special role of geocells in soft soil foundation treatment is firstly manifested in that it forms double-sided friction with the filling material, which effectively limits the lateral movement trend caused by the load; secondly, the direct reaction between the cells and the cells is more Part of the tendency of lateral displacement due to load is offset, so that its bearing capacity is improved and settlement is reduced.
The friction between the geotextile and the foundation soil makes the tensile stress in the soil transfer to the reinforcement, the reinforcement bears the tension, and the soil between the reinforcement bears the pressure and shear stress, so that the reinforcement and soil in the reinforced soil can play well. The respective potentials make the soil compact, enhance the integrity and continuity of the soil, and limit the lateral deformation of the soil.
(1) Compared with other flat geosynthetic materials such as geotextiles, geogrids and geotextiles, the geocell is a three-dimensional structure. By changing the height of the cell or the combination of the cell plates, rigidity, semi-rigidity, etc. can be obtained. Plates of completely different nature.
(2) Compared with the plane structure of geogrid and geotextile, the geocell has a certain thickness, so it has the ability to resist bending and can diffuse the vertical stress transmitted from the upper part.
(3) Geocells can be stacked, which is more convenient for storage and transportation than geogrids and geotextiles.
(4) Geocell is a new type of geocomposite material, and the mechanism of its reinforced structure needs to be further studied.