Building over soft subsoils
Building over soft subsoils with geosynthetics
Geosynthetics can be used in a variety of ways for capping, covering, sealing and reinforcement of soft soils. They offer an economic, lightweight solution to different environmental conditions.
Reinforcement
When reinforcing large areas of very soft subsoils, one of the most challenging engineering aspects is to make the area suitable for traffic or construction. Combigrid® can be placed directly on soft subsoils to immediately improve soil bearing capacity. Combigrid® offers the advantages of two materials with the simplicity of installing a single product, as it is a composite product combining the reinforcing properties of Secugrid® geogrids with the separation and filtration properties of Secutex® nonwoven geotextiles.
When used in conjunction with a nonwoven geotextile, the robust monolithic flat bars of the Secugrid® geogrids distribute point loading homogeneously through the grid to a larger surface area. This load distribution results in a reduction in local deformation and improves the bearing capacity of the soft subsoil.
The load distribution characteristic (snow shoe) of Combigrid®, enables placement of a mineral soil cover layer, while at the same time the separation properties of the integrated Secutex® geotextile ensure that two differing soil types do not intermix.
Sealing
In sludge lagoon capping applications where highly contaminated substances must be controlled, geosynthetic solutions by Naue will ensure their long-term containment. Similar in concept to soft soil applications, Combigrid® products offer load-distributing characteristics, enabling lightweight equipment to traffic the liquid surface.
High density polyethylene (HDPE) Carbofol® geomembranes provide a virtually impermeable seal to water and gases. They are inert to the aggressive chemicals that are most often present and can be securely welded to form a uniform barrier to the intrusion of rainwater or the escape of gases. To protect Carbofol® geomembranes from excessive deformation as well as the possibility of puncture by sharp edged stones present in the mineral cover soil/drainage layer, a heavy weight mechanically bonded nonwoven cushion geotextile (1,200 g/m² or above) can be installed directly over the geomembrane.
Bentofix® geosynthetic clay liners are well suited to sealing subsoils that are susceptible to large settlement. Bentofix® uses high quality, natural sodium bentonite encapsulated between two geotextiles. Once hydrated, the high swelling bentonite creates a seal against liquid and gas flow. Using high elongation, mechanically bonded cover and carrier nonwoven geotextiles, the uniform needle-punched structure of the Bentofix® can endure deformation of over 30 %. The installation of Bentofix® in a rain-lap orientation will ensure that the seal is not compromised, even after consolidation induced settlement.
Vertical drains
Consolidation is a slow process where excess pore water is released in relationship to an applied stress. However, as the pore water must have a path to escape, Secudrain® vertical drains are commonly installed into the consolidating soil. Secudrain® vertical drains are approximately 100 mm wide and are made from a coarse-fibre nonwoven geotextile drainage core encapsulated between two nonwovens. With this flexible composite structure, Secudrain® vertical drains have longterm filter stability, and are especially suitable for use in soft subsoils that may be susceptible to settlement. With installation equipment termed “stitchers”, Secudrain® vertical drains are rapidly positioned and “stitched” into the saturated soil. Secudrain® vertical drains substantially reduce the consolidation time of soft, relatively impermeable soils.
Gases beneath the sealing system can also be collected and discharged with a cost-efficient Secudrain® drainage system. Secudrain® is effortlessly unrolled by one man and can be covered with Carbofol® or Bentofix® liner. When used above the Carbofol® or Bentofix®, Secudrain® is also a cost efficient alternative, offering protection, separation, filtration and drainage – all in one product.
Conclusion
With their superior soil reinforcement characteristics, Secugrid® and Combigrid® products improve soil bearing capacity, permitting traffic and construction to occur over soft subsoils. Secutex® nonwoven geotextiles offer excellent protection for Carbofol® geomembranes. Where differential settlement is expected, the more flexible, Bentofix® geosynthetic clay liners can be used in place of Carbofol® geomembranes. To accelerate consolidation, filter-stable, flexible Secudrain® vertical drains can be “stitched” into the soil. Gas as well as rainwater can be discharged by Secudrain® synthetic drainage systems depending on where it is deployed. Geosynthetic solutions are often the only option for the rapid capping and sealing of soft subsoils. Naue is the ideal choice when geosynthetic solutions are required.
