Geotube Structure

• Outer Material (Main Bag Fabric)

  The main body is made of high-strength polypropylene (PP) or polyester (PET) woven geotextile, which offers excellent tensile strength, UV resistance, and chemical resistance. The fabric's pore size is precisely designed to allow liquids to drain freely while effectively retaining solid particles.

  
  

• For demanding projects, a double-layer structure is employed: an outer layer of high-strength load-bearing fabric and an inner layer of filter fabric to enhance overall dewatering efficiency and safety.

  
  

• Filtration and Drainage System

  The design of the Geotube's filter fabric is crucial. The pore size (AOS) of the filter fabric is generally between 0.2 and 0.6 mm and is determined based on the filler particle size distribution. The appropriate pore size ensures efficient water filtration without clogging, thus ensuring a stable dewatering rate.

   

• Seams and Reinforcement

  The bag's seams are double- or triple-stitched, and some high-pressure applications also utilize heat or ultrasonic welding. The tensile strength of the seams must be greater than 70% of the bag itself to prevent cracking due to increased internal pressure during grouting.

   

• Feed and Drain Ports

  The bag is typically equipped with multiple feed ports on the top to facilitate even slurry injection. Drain holes or diversion channels are located on the bottom or sides to facilitate liquid drainage.

How the Geotube Works

The core principle of the Geotube is solid-liquid separation. It achieves volume reduction and drying of slurry or sewage sludge through a combination of physical filtration and gravity dewatering.

• Filling Phase

  Slurry with a high water content (generally 1% to 10% solids) is pumped into the Geotube via a pumping system. As the injection volume increases, the bag gradually expands and forms a stable cylindrical structure.

  
  

• Dewatering Phase

  When the slurry is full, hydrostatic pressure builds up inside the bag. Liquid is forced through the filter cloth under pressure, while solid particles are trapped inside the bag. Gravity and capillary action accelerate water removal. Adding a polymer flocculant (PAM) can significantly increase the speed of slurry-water separation.

   

• Solidification and Stacking Phase

  Over time, the solids inside the bag gradually compact and dry, and the moisture content decreases. After 1 to 2 weeks, the solids inside the bag reach a stable state, with a volume reduction of 60% to 80%. At this point, the bag can continue to be used as a dam, revetment or wave-breaking structure, or the dried solid can be reused or disposed of harmlessly.

The main factors affecting Geotube size design

Filler Properties (Slurry or Sludge Properties)

• The primary function of a Geotube is solid-liquid separation, so filler properties are the primary factor influencing sizing.

  
  

• Solids Content

  The higher the solids content, the denser the slurry, the greater the mass of solids per unit volume, and the higher the required internal bag pressure. Low solids content (e.g., 1–3%) requires a larger bag volume to accommodate more water.

Geotube Bag Material and Structural Design

• Fabric Strength

  The tensile strength of the bag is generally required to be ≥70 kN/m. If high filling pressures are expected, high-strength PET or a double-layer reinforced structure should be used to prevent expansion or rupture.

   

• Filter Cloth Aperture Size (AOS)

   A pore size that is too large will cause solids to escape; a pore size that is too small will hinder drainage. The appropriate AOS (typically 0.2–0.6 mm) should be selected based on the filler particle size distribution.

   

• Seam Strength and Welding Method

  The seam strength must be at least 70% of the bag's overall strength. Heat welding or triple-stitching techniques can improve safety.

Foundation Bearing Capacity and Installation Conditions

The stable operation of Geotubes requires a solid foundation. Weak or uneven foundations can lead to uneven settlement, bag distortion, or cracking.

Design considerations include:

Foundation bearing capacity (kPa): If the foundation is less than 50 kPa, a cushioning layer or non-woven fabric backing is recommended.

Impermeable layer design: In dewatering projects, an HDPE membrane or clay layer is typically required to prevent leakage and contamination.

Layout space: The bag length is generally controlled between 25–100 meters, adjusted according to the site topography.

Single-Layer and Multi-Layer Stacking

Depending on project requirements and available site space, Geotubes are typically arranged in two different configurations:

Single-Layer Placement

Single-Layer placement is suitable for applications with slow water flow, low stack height requirements, or limited foundation bearing capacity. Single-layer structures offer uniform load distribution, simple construction, and easy maintenance. They are commonly used in:

• River management and bank protection;

• Small-scale mudflat reclamation;

• Temporary sludge dewatering storage areas;

Agricultural irrigation canal reinforcement, etc.

Multi-Layer Stacking

When a higher protection height or larger water storage capacity is required, a multi-layer stacking structure can be used. Typically, a "pyramid" or "stepped" stacking arrangement is used, with the upper Geotube placed between two lower Geotube bags to distribute load and provide overall stability. Multi-layer stacking is widely used in:

Coastal protection projects;

• Large-scale reclamation projects;

• Temporary embankments;

• Port expansion projects, etc.

Safety and Maintenance

The safety and maintenance of Geotube systems are critical to ensuring the long-term stability of projects and extending the service life of structures. Whether used for dewatering, cofferdams, flood control, or coastal protection, sound safety design and regular maintenance strategies can effectively prevent structural failure, material damage, and environmental pollution. This section systematically discusses structural safety, anti-seepage and anti-damage design, monitoring and maintenance plans, repair and replacement strategies, and environmental and construction safety management.

Abrasion and UV Resistance Design

• When used near coasts, in rivers, or in exposed environments, protective layers are required to resist long-term physical and chemical attack:

• Cover the surface with non-woven fabric or gravel to prevent wave and wind erosion;

• Select polypropylene (PP) or polyester (PET) materials with UV-stabilized masterbatch;

• Exposed areas can be sprayed with a protective coating or covered with sunshades.

Anti-seepage and Drainage Design

The knitted or woven fabric of Geotubes is water-permeable, enabling internal dewatering and mud-water separation. However, in anti-seepage applications (such as cofferdams or solid waste packaging), the following should be implemented:

• Add an HDPE film or double-layer structure to the outer layer;

• Design dedicated drainage holes and a diversion system to prevent water pressure buildup inside the bag;

• Establish detection wells or monitoring points to monitor seepage changes in real time.