2 Causes of geotextile failure
( 1 ) When geotextile or geomembrane are laid on the bed surface with poor filling density, non-conforming road arches, and excessive surface convexity and concavity (including sleeper pressure groove, mechanical pressure groove, and gun pit backfill soft rock and soil), the material laid will be deformed with the uneven sinkage of the bed surface (the sinkage of the stress area under the rails is the largest, showing a clear concavity), and the force will increase continuously with the concavity of the bed surface, and finally the material will be torn, and then the submerged water gathered on it will soften the soil layer. The soil layer is softened by the infiltration of water underneath it, or by the rise of capillary water. The continuous wedging of the ballast causes the creation and development of new grooves, which in turn extend the damage to the material. If the soft plastic layer beneath the laid material is thin and the underlying soil layer has a high load-bearing capacity, the damaged material is forced out along the foot of the roadbed together with the coarse sand protection layer and soft plastic soil above and below it, and in some cases, the material is even broken into “strips” (mostly neoprene and plastic sheeting, because of the large difference in the longitudinal and transverse tensile strength of such materials). The difference in longitudinal and transverse tensile strength of these materials is large.
(2) The elevation of the top surface of the road shoulder surface or the inner wall of the side trench is higher than the elevation of the geosynthetic material laid, so that water is gathered at the boundary between the geotextile fabric material and the soil, and the infiltration of water makes the soil soft and expand continuously, which not only makes the geosynthetic material easy to break, but also causes the slump of the embankment slope along this boundary, and the inner wall of the side trench of the road graben is squeezed down.
(3) When laying geocomposites, the sink and ballast pockets were not thoroughly treated, the subgrade and surrounding subgrade soils were still in a soft plastic state, the transverse drainage slope and longitudinal drainage slope of the subgrade were not well done, a number of water-collecting depressions were formed, the coarse sand protection layer was not sieved, and the stones containing ballast or angular stones were not compacted (especially the bottom protection layer). As a result, the surface of the geocomposite material is uneven, and under the dynamic load of the train, the ballast rubs the surface of the material, wedging the ballast in the concave parts and piercing the material, resulting in “ineffective geotextile laying“.
(4) Geomembranes with low strength index, low elongation, uneven thickness, or even a large number of pores or holes are quickly destroyed after laying due to their poor quality and the slightest unfavorable factor. In addition, geomembranes piled up in the open air or used as “scaffolding cloth” will be damaged quickly when the material is exposed to the sun.
(5) Inappropriate selection of geocomposite materials. The use of geomembranes or geotextiles in areas rich in underground water or the mismatch between the pore size of the geotextile and the fine particle size of the soil can affect the effectiveness of the application. In summary, the main purpose of laying geomembranes or geotextiles is to intercept and drain water, and to improve the uneven distribution of dynamic stresses.
3 Countermeasures to prevent geotextile failure
3.1 New railroad laying
New roadbeds must be laid with excellent fill density and bed surface shape and dimensions. At the same time, the thickness of the coarse sand protection layer should be appropriately thickened and fully compacted within the range of I OOC m to the left and right of the rail location.
3.2 The existing line laying
- The longitudinal and transverse distribution of the trap and ballast should be investigated in detail during the survey stage. At present, the use of excavation, brazing methods have been more primitive, the accuracy is far from meeting the requirements, it is recommended that the use of electrical detection method. At the same time, to groundwater conditions, slope weir, reservoir distribution, `take the pit water and capillary water up to the height of the investigation, should also be soil samples for geotechnical testing.
- The design should be based on the longitudinal and transverse distribution of the trap, ballast, the longitudinal section of the line and shoulder, the existing side ditch condition, soil quality, to determine the transverse drainage slope (generally) 3% and longitudinal slope location and length (if necessary, set up transverse blind ditch), according to the distribution of groundwater and rift top weirs, ponds, water fields, irrigation ditches, reservoirs, and soil quality, consider whether it is necessary to set up longitudinal seepage blind ditch and other Consider what kind of geosynthetic materials and their specifications. In short, it is required that the bearing capacity of the foundation bed is not less than 150 kPa and that the interception and drainage are good.
- During construction, in addition to strictly following the design requirements, special emphasis should be placed on checking the lateral drainage slope with a slope gauge, checking the load-bearing capacity with an easy-fall hammer, and the protective layer of medium and coarse sand must be rammed. It is also recommended that the sand for the protective layer be sieved and shipped in chemical fiber bags to prevent ballast mixing, reduce sand consumption and improve work efficiency.
- Strictly test the materials and prohibit the use of materials exposed to sunlight.