Mountainous Expressway Tunnel Anti-seepage Protection Project (Composite of Filament Geotextile + Geomembrane)

Ⅰ. Tunnel Geotextile Project Overview

The project is a two-way four-lane expressway tunnel located in mountainous area, with a total length of 2860m. The surrounding rock is mainly weathered rock and broken rock stratum, with abundant underground fissure water, and water gushing and seepage problems exist in local areas.

Main Risks:

Water seepage of tunnel lining, freeze-thaw damage, sediment loss of surrounding rock, and puncture of waterproof layer by sharp rocks.

Adopted Materials:

300g/㎡ needle-punched filament geotextile matched with 1.5mm HDPE geomembrane, which are used as cushion layer, filtration layer and protection layer respectively.

Ⅱ. Tunnel Geotextile Application Details

After the initial support shotcrete construction is completed, clean up sharp protrusions and bolt heads on the rock wall, then lay the geotextile.
The geotextile is fully laid between the rock wall and the geomembrane, with the lap width ≥ 80cm, and is fixed with hot melt gaskets.

‌Functions of geotextile‌: Isolate the surrounding rock from the anti-seepage geomembrane, buffer the edges and corners of rocks to prevent puncturing the geomembrane; meanwhile filter the seepage from surrounding rock, discharge fissure water, and avoid water pressure bursting the waterproof layer.
The composite waterproof system is formed by the combination of geotextile and geomembrane, before the secondary lining concrete is poured.

Ⅲ. Main Functions

‌Protection‌: Protect the HDPE geomembrane from being punctured by rocks and bolts

‌Filtration‌: Filter sediment to prevent blockage of the drainage system

‌Drainage‌: Divert fissure water in surrounding rock to reduce water pressure

‌Isolation‌: Separate concrete from surrounding rock to improve structural durability

Ⅳ. Implementation Effect

No large-area seepage or water leakage occurred along the entire tunnel, and the drainage system is unobstructed; the waterproof layer remains intact with no damage or leakage; the structure has been stable for many years of operation, with no freeze-thaw damage, and the service life of the waterproof system has been greatly improved.