Soil Nails

Solving problems with soil nails in IA, KS, MO and NE

Soil nail installation for commercial applications

Experienced foundation repair specialists and geotechnical engineers appreciate soil nails for their ability to solve soil stabilization problems in cost-effective ways. For example, when a basement foundation must be excavated right next to an existing building with a slab foundation, it’s critical to prevent the soil next to the slab from caving into the excavation.

Soil nails, used in combination with shotcrete, enable the contractor to quickly and inexpensively construct a retaining wall that stabilizes the excavation while the new basement foundation is under construction.

It’s also possible to construct permanent retaining walls with soil nails and shotcrete. This technique is faster, easier, less expensive and less disruptive than building the same wall with poured concrete or concrete masonry units (CMUs).

A soil nail retaining wall can be built from the top down, in increments of 6ft. or so (See “Building a soil nail and shotcrete retaining wall” below). But a poured concrete or CMU retaining wall must be built from the bottom up. This necessitates a complete, full-depth excavation at the start of the project, a scope of work that may be too major and too disruptive in some locations. Soil nailing has become popular because it eliminates or minimizes these impacts.

Building a soil nail and shotcrete retaining wall

Like a conventional concrete retaining wall, a retaining wall that utilizes soil nails is an engineering exercise involving soil analysis, loading calculations and other important design factors. Once the work begins, there are three basic steps:

  1. Making a shallow excavation. The first cut (typically 3ft.-6ft. deep) defines the top of the retaining wall. Curved walls are nearly as easy to construct as straight walls —another advantage with this technique.
  2. Installing soil nails. Soil nails come in different sizes, lengths and designs. Helical soil nails are designed to be self-drilling, while others are designed to be jacketed in grout that is pumped into a pre-drilled hole. During the wall design process, engineers will determine the type, size and spacing of soil nails to be used based on wall height and soil characteristics. Workers use hydraulic equipment to drive each soil nail into the excavated wall, aiming the nail slightly downwards.
  3. Adding a shotcrete facing. When all nails have been driven, workers apply a shotcrete facing that’s usually between 3 in. and 6 in. thick. Drainage matting material and steel mesh are sometimes incorporated into this spay-applied wall. Promoting good drainage helps to prevent hydrostatic pressure from building up behind the wall. The steel mesh is included to increase the strength of the concrete.

When these three steps are completed, a second excavation is made and the same three steps are repeated. This 3-step construction cycle continues until the wall reaches its final design height.

Used in combination, soil nails and shotcrete give foundation repair contractors a number of problem-solving options that are useful to residential and commercial customers alike. Being able to build retaining walls quickly and inexpensively makes it possible to create workable level areas on sloping sites that would otherwise be unusable. Soil nail and shotcrete techniques can also stabilize slopes and create temporary walls so that more permanent structural work can take place safely.