**1. Introduction**

The application goal of geonets is mainly for planar drainage, and it is used as a medium to safely discharge the leachate generated from the landfill to the outside of the landfill. The two strands are cross-bonded to form a network structure in geonet, which serves as a drainage passage for the liquid. Geonet products of various structures are used and drainage capacity of geonet is very important because the landfill service life is determined by geonets drainage capacity when designing landfill.-

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Fannin [1] investigated the factors influencing the drainage capacity of geonets, and confirmed that the flow rate depends on the structure of the geonet and the drainage capacity is smaller when the strand channel and the crossing angle of the geonet are large.

Also, Zhao [2] analyzed the factors affecting the drainage performance of geonets and confirmed that the drainage capacity decreases as the hydraulic gradient and the compressive strength increase.

To investigate the behavior of geosynthetics under high normal stresses, Narejo and Rad et al. conducted a transmissivity test with normal stresses up to 2000 kPa [3–5]. From the results showed the variation of geonet transmissivity with normal stresses. Geonets behaved similarly up to 200 kPa regardless of weight. However, in the case of geonet with a small strand crosssection area thickness, the drainage performance decreases when the compressive strength increases, but the drainage performance does not decrease much even when the maximum confining load is 2000kPa for thicker geonets. This is probably due to the fact that as the thickness- of the strand cross-section layer constituting the geonet becomes smaller and the compressive strength becomes larger, the roll-over of the strand intersection of the geonet occurs more often.

Koerner [6] analyzed the roll-over phenomenon of bi-planar geonet. According to this, since the upper and lower strands constituting the geonet are not vertically bonded to each other at the cross-section areas, when the compressive strength is applied to the upper and lower layers of the geonet, the drainage capacity is large at the initial stage, the deformation of the strand joint starts to occur. This roll-over phenomenon causes a change in the drainage capacity in the upper and lower layers of the geonet, and the drainage capacity of the geonet is decreased and the drainage performance is lowered with time.

Allen [7] analyzed the effect of orientation of strand constituting geonet on drainage performance. In the case of the lower strand with small inclination angle at the cross-section area of the upper and lower strands, the roll-over phenomenon occurs more than the upper strand, and the drainage performance deteriorates.

Kopp reported that geonet drainage performance was affected by the construction site temperature when the geonet was constructed at the landfill site [8]. Pegg indicates that the drainage performance of the geonet is most affected under the circumstance at 80 or 85°C in the landfill site [9].

Therefore, when the environmental temperature is increased, the mobility of the molecular chain of the polyethylene, which is the raw material of geonet, becomes larger, and the drainage performance may be decreased due to the structural change of the geonet to the compressive strength.

In this chapter, the variation of drainage performance of geonets used for horizontal drainage is analyzed in relation to the influence of constraint load related factors.-
