Analysis of interface shear failure and peak strength of geomembrane and polyester filament geotextile

Analysis of interface shear failure and peak strength of geomembrane and polyester filament geotextile

Geosynthetic materials such as geomembranes and geotextiles are widely used in fields such as environmental protection, transportation, water conservancy, agriculture, and construction waterproofing. Since the shear strength between geosynthetic materials interfaces is weak, the slip stability of slopes containing geosynthetic materials is often determined by the shear strength between geosynthetic materials.

In the following content, the geomembrane is referred to as GM , the rough geomembrane is referred to as GMT , the smooth geomembrane is referred to as GMS , and the polyester filament geotextile is referred to as GT .

The roughness of the geomembrane surface greatly affects the peak shear strength of the interface with the geotextile. According to the GM/GT interface shear test, it was found that the interface peak shear strength of GMT/GT was significantly higher than that of GMS/GT, and The horizontal displacement corresponding to the peak stress is also larger. The damage forms of the geosynthetic interface include: the fibers on the surface of the non-woven fabric are pulled out or torn, and the rough ridges on the GMT surface are damaged or smoothed during the interface shearing process. In addition, the forms of interface damage are affected by different factors. The influence includes: normal load, rough surface forming process and rough surface convex distribution, etc. The influence of the rough surface spacing is two-fold. Generally, the smaller the rough surface protrusion spacing, the greater the enhancement effect of the interface shear strength.

However, when the rough surface protrusion spacing exceeds a certain degree of closeness and is too compact, it will cause GMT. The surface becomes even and smooth. The effect of rough surface protrusions will be significantly reduced, and the interface shear strength will also be reduced. Figure 1 is a comparison of samples of two flat extruded rough facial masks with different spacing between roughened protrusions.

Figure 1 Comparison of samples of flat extruded rough facial masks with different spacing between roughened protrusions

In order to have a deeper understanding of the interface damage between GM and GT and to quantify the relationship between the two interfaces, comparative experiments under different conditions were conducted using a direct shear instrument. The experimental data restores and simulates the interface interaction between GMT, GMS and GT of different weight specifications during engineering applications to the greatest extent, which is beneficial to the selection of geosynthetic materials such as GM and GT under different engineering application environments. Table 1 and Table 2 below show the mechanical performance indicators of 1.5mmGMS and 1.5mmGMT. The polyester filament geotextiles used in the test are 100g, 300g, 400g and 600g.

Table 1 Mechanical parameters of glossy mask (GMS)

Table 2 Mechanical parameters of extruded rough facial mask (GMT)

Figure 2 Illustration of the direct shear instrument used in the experiment

Figure 3 Experimental samples and filling process

For the GM/ GT interface shear test, the normal stress used after the test installation is completed is selected from 50, 100, 200, 300 and 400kpa, and the interface shear test rate is 1.0mm/min.

Interface shear stress-horizontal displacement relationship between 1.5mmGMS and 300gGT:

Figure 4 GMS/GT interface shear stress-displacement relationship

As shown in Figure 4, when shearing begins, the shear stress increases rapidly with horizontal displacement and reaches a peak value. The peak shear strength corresponds to a horizontal displacement of 2~3 mm. Then the shear stress decreases with horizontal displacement at a rapid rate and becomes stable. , as the normal load increases, the strain softening phenomenon becomes more obvious. There was no obvious damage on the surface of GMS and GT after the shear test.

Interface shear stress-horizontal displacement relationship between 1.5mmGMT and 300gGT:

Figure 5 GMT/GT interface shear stress-displacement relationship

As shown in Figure 5, when shearing begins, the shear stress increases rapidly with the horizontal displacement and reaches a peak value. The peak shear strength corresponds to a horizontal displacement of 4~5mm. Then the shear stress slowly decreases with the horizontal displacement to the residual strength, which is consistent with GMS/ The same rule as GT, as the normal load increases, the strain softening phenomenon becomes more obvious. After the test, the fibers on the GT surface were pulled and damaged, but there was no obvious damage on the GMT surface.

Figure 6 GMT/GT peak shear strength envelope under different normal loads

As shown in Figure 6, ignoring the cohesion component that has a small impact on the shear strength of the geosynthetic interface, and fitting the peak shear strength of GMT/GT under different normal loads through the origin, the corrected geosynthetic Shear friction angle of composite materials. Table 3 shows the shear friction angle at the interface of different geosynthetic materials . Compared with the GMT/GT interface, the peak friction angle of the GMS/GT interface is reduced by 10.1°.

Table 3 Geosynthetic interface shear friction angle

Table 4 shows the interface shear peak friction angle obtained from the shear test

between 1.5mm GMT and GT of different specifications .

Table 4 Shear friction angle at the interface between 1.5mmGMT and GT of different specifications

It can be seen from Table 4 that the interface shear peak friction angle between 1.5mmGMT and polyester filament cloth with different weight specifications increases as the weight of the geotextile increases. The peak friction angle of 600g polyester filament geotextile The angle can reach 28.4°, and the average roughness height of the extruded rough geomembrane in this test type is 0.70mm. The friction angle of the 100g geotextile with a lower weight does not comply with the above rules. The friction angle is higher than that of the 300g geotextile. However, the 100g geotextile has a lower strength index and a thinner cloth surface. The damage after shearing is different from that of the high weight geotextile. There are differences between fabrics, and they need to be carefully selected in engineering applications, especially in slope systems.

The interface shear peak friction angle between GMT under different nail type distribution densities and GT with different weight specifications can be seen in Table 5 . The distribution density of nail types is shown in Figure 1. The left side of Figure 1 shows a larger distribution density with an average roughness height of 0.65mm, recorded as GMT-1. The right side of Figure 1 shows a smaller distribution density with an average roughness height of 0.70mm, recorded as GMT-1. GMT-2.

Table 5 Interface shear friction angle between GMT under different nail type distribution

densities and GT with different weight specifications

It can be found from Table 5 and Figure 1 that although the roughness height of GMT-1 of 0.65mm is lower than that of GMT-2 of 0.70mm, its peak friction angle is higher than the data of GMT-2. Therefore, a reasonable nail density distribution can make up for this. The friction angle is low due to insufficient roughness height. In the test of two types of rough geomembranes, the 100g geotextile showed a high friction angle and was easily damaged, which once again confirmed the conclusion drawn in Table 4.

Through a series of comparative tests with direct shear methods, the following conclusions are reached:

• The GMS/GT interface shear appears as pure friction between materials, and the interface cohesion is weak. When the normal load increases, the peak phenomenon gradually becomes obvious. The shear displacement is small, and the peak strength can be reached at 2mm. After the peak, it can quickly reach a relatively stable strength under large displacement.
• The rough surface protrusions of GMT can be embedded inside the geotextile fiber under the action of stress load, and the pull-out effect can significantly enhance the interface shear strength. Compared with GMS, the pull-out effect also increases the horizontal displacement of the interface peak, achieving a stable Large displacement intensity is relatively slower.
• The pull-out effect is the main factor responsible for the high shear strength of the GMT/GT interface. In addition, it is also affected by the height of the rough surface of the geomembrane itself, the distribution density of the rough surface ridges, the molding process, the material properties and the fiber length of the geotextile. Influence.
• The friction angle data of the 100g geotextile is relatively high. However, due to the low mechanical properties of the geotextile of this specification and the light and thin cloth surface, it is easy to cause serious damage to the cloth surface. In the application of slope engineering, it is easy to cause the risk of instability, so caution is required. Selection and design.