Geotextile layer

A Geonet drainage layer can be chosen if the HELP model shows it to be more effective than sand in controlling leachate production and is comparable in cost. It is assumed that the HELP model predicts a 75 to 80% reduction in leachate production. A Geotextile layer would be laid on either side of the Geonet drain to prevent clogging. A minimum slope of 3% would be provided to meet state requirements. 

Unimpeded flow of water through granular filter or geotextile layer without significant washout of fines (small particles) from natural soil. 

In some drainage and filtration applications of geotextiles, layered nonwoven fabric may perform better than single-fibre nonwoven structures. The layered fabrics are produced by needle-punched bonding, in which two or more separate layers of fibre webs are made from fibres with different linear densities (Hwang, Lu, Lin, 1999 Rakshit, Patil, Balasubramanian, 1990). 

Care must be taken with the installation under water because the filter sheet will float and will not sink into the desired position under its own weight. Even when the fabric is polyester, a material with a density higher than water, it will float owing to air bubbles trapped between the fibres. Placement can be eased with a so-called sandmat , two geotextile layers with a sand fill of 5—9 kg/m kept between. The two sheets are needlepunched or sewn in short distances to reach a good shear resistance and to keep the sand fill in place during the placement procedure and on slopes under working loads. 

Calculate the number of geotextile layers the first layer of reinforcement is always positioned at the base of the slope. The other layers are calculated starting from the base. With reference to Table 15.6, the procedure is as follows ... 

A circular failure surface is assumed and the soil encompassed by such surface is divided into many slides divided by vertical surfaces. Eor each, it is possible to calculate the active moments caused by the thrusts of the soil and the resisting moments resulting from the frictional and/or cohesive forces and the tensile strength in the geotextile layers (Fig. 15.18) the FS is calculated as the ratio of the sum of the resisting moments and the sum of the active moments. Numerous circular surfaces are investigated for each, the FS is calculated as follows (Eq. [15.45]) ... 

To determine the vertical spacing of the geotextile layers, earth pressures are assumed to be linearly distributed using Rankine active earth-pressure couditions for the soil backfill and the surcharge. 

Then, the same free body approach can be taken to obtain the length of embedment of the geotextile layers in the anchorage zone, Lg- When these values are obtained, they... 

Now, using Eq. [15.55] for varying depths, calculate the geotextile layer spacings. 

Nongeosynthetic solution 1.2 m thickness of selected coarse aggregate Geosynthetic solution 0.6 m thickness of selected coarse aggregate and reinforcing geosynthetic (ie, geotextile) layer (Fig. 26.4)... 

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