Retaining Walls

 

Retaining wall finishes for Purposes

The Purpose of a Retaining Wall

  • To hold in or hold out soil, fines and water
  • To recover usable space on a sloping site
  • A beautifying addition to a suitable space
  • A structural element to support indirectly a significant structure [building,swimming pool etc]

Importance of a retaining wall

Rule of thumb over 1200mm in height requires an engineers design. You don’t want to see a failed retaining wall. Engineers can design gravity walls or concrete/concrete block and steel walls to retain. Screw piles can be a good option for securing retaining walls..
                                                                                                                                                                           Reclaiming the back yard

Retaining Wall Collapse

Can be messy and expensive to fix. Underpinning of this retaining wall will be necessary before wall can be reinstated. Below is one approach.

Screw Piles as Soil Nails

Developments in soil nail technology have made this system of earth retention popular for excavation shorings, slope stabilization, and retaining walls. It is  a cost-effective
method of ground reinforcement for earth retention without excavating and hence spoil. Soil nails have been traditionally grout piles with a threaded rod embedded [ eg 3m long 150mm diameter  24mm threaded rod.]

 Soil Screw Retention Wall Systems reinforces the earth in conjunction with shotcrete facing to construct a gravity walls. Its speed and bearing mode make this option a cost-effective and time-efficient alternative to traditional soil friction retention systems. In this “soil nail” application, Soil Screws acts in a bearing mode instead of a friction mode like that of a grouted anchor.

Quickier soil nailing

The Soil Screw pile anchor system removes performance uncertainties and costs associated with grouted soil nails in low shear strength soils. You know the capacity of each screw because it is directly related to the amount of torque applied at time of insertion and each screw torque is recorded for quality control. These helical soil screws are easy to store, reusable and cut down on man power and equipment needed to anchor an engineered wall when repairing or installing a foundation or stabilizing a road embankment. Hence forth it is a more economical option. For rock embankments rock bolts are used and grouted in place. [Perhaps a 50mm diameter hole 2m long. Length of rock bolt is governed by the solidity of the rock…how many fractures it has.]

Composition of the Soil Screw

Soil Helical blade piles are generally seated at a shallower depth than helical tieback anchors when installed to retain similar soil masses. Bearing plates are spaced along the entire length of the helical screw anchor, and the true-spiral helices install with ease for minimal soil disturbance. Most importantly, the helical soil screw Anchors are not tensioned after installation; they are passive elements. When a Soil Screw Retention Wall System is installed, it holds the soil as a single mass of sufficient internal stability. Monitoring torque during installation accurately indicates expected holding capacity for predictable results so no retro anchor testing is required like a grout pile pull out test.

Common equipment, such as mini-excavators  can quickly rotate the soil screws into place. Anchor size and grid spacing are designed to local soil conditions and load requirements.

Screw soil nail advantages over grout piles:

  • Lower installation costs vs. traditional methods
  • Fast, clean installation
  • No grout – immediate loading
  • No spoils to remove off sit
  • Installs in limited access areas

The helical soil nail consists of helices attached at regular intervals to the entire shaft,including extensions. The result is a helical device with helices spread along the entire length of shaft.The common helical soil nails are 2.1 m long lead or extension with 200 mm diameter helices spaced at 700 mm intervals along the shaft.

 

Inserting soil nail

Augering a soil nail

 

 

Engineering Drawings

An engineer will be needed to draw up details for any structural retaining wall as failure is not an option.

Engineers drawing retaining wall

Structural Details concepts for typical applications

Help manual by Boral: http://www.boral.com.au/masonry-design-guide/pdf/BOR11999_SA_Manual_Bk4.pdf

Links: http://en.wikipedia.org/wiki/Retaining_walls