Place geosynthetics between two different materials, or between different particle sizes of the same material, and between the foundation and the foundation to separate them. When the external load acts, it is not their mutual mixing or loss to maintain the overall structure and function of the material. Generally, when building roads, the subgrade and roadbed are constructed in sequence, and the road will be put into operation after the completion of construction. Because of the load pressure and the passage of rain, the subgrade, roadbed materials and general materials are mixed together. Although this is a local phenomenon, the strength of the original design and the drainage and filtration functions are weakened. In order to prevent the occurrence of this phenomenon, geosynthetics can be set between two materials with different characteristics, so as not to mix them, but to maintain a unified role.
In railway engineering, the geopolymer is laid to maintain the stability of the track and reduce the maintenance cost: in road engineering, it can play the role of permeability membrane to prevent the soft soil layer from invading the crushed stone of the subgrade, otherwise it will cause mud boiling, and finally reduce the design thickness of the subgrade and roadbed, resulting in road damage; In terms of foundation reinforcement, it can separate the newly built foundation from the original ground base, enhance the bearing capacity of the foundation, and facilitate drainage and accelerate soil consolidation; The storage box for materials can avoid the loss and deterioration of materials, and also help to prevent pollution for waste materials. The permeability of geosynthetics used for isolation shall be greater than that of the isolated soil; When bearing dynamic load, geosynthetics should also have sufficient wear resistance. When there is no water flow between the isolated materials or soil layers, impermeable geomembrane can also be used.