Document ID: chunk:federal_register_of_legislation:F2016L00416:reg:4:p17
Version: federal_register_of_legislation:F2016L00416
Segment Type: reg
Provision Reference: reg 4 (pt 17/21)
Character Range: 74657–77348

Design.

Figure 14 Steel trench sheeting and jacks

Timber soldier sets
The soldier set is a simple form of trench support set which can be formed with steel or timber. This system is mostly used in rock, stiff clays and in other soil types with similar self-supporting properties.
Unlike closed sheeting sets, soldier sets retain the earth where there may be a fault in the embankment. Soldier sets only provide ground support at regular intervals and do not provide positive ground support to the whole excavated face. Open soldier sets are only suitable for use in stable soil types. (see Figure 15).

Figure 15 Timber soldier sets

Closed sheeting
Closed sheeting is where vertical timber or metal members are used to fully cover and support
a trench wall and which are in turn supported by other members of a ground support system.

Figure 16 Example of closed sheeting

Side lacing is a form of closed sheeting used primarily to ensure worker safety by preventing soil from slipping by the placement of fill behind timber boards or steel plates (see Figure 17). Side lacing is used in all types of ground, and is particularly useful where long or large diameter pipes are to be installed and in variable ground conditions where steel or timber supports are difficult to install. Side lacing should be firmly wedged into the ground to prevent it from moving when fill is placed against it.
When closed sheeting or side lacing is used to prevent ground collapse, workers should not:
    * enter the excavation prior to the installation of the sheeting/lacing
    * work inside a trench, outside the protection of sheeting/lacing
    * enter the excavation after sheeting/lacing has been removed, and
    * enter an area where there is sheeting/lacing, other than by a ladder.
Figure 17 Side lacing in sand trench

Ground anchors
A ground anchor is a tie back to the soil behind the face requiring support and is typically used
with steel sheet piling (see Figure 18). Ground anchors may be installed in either granular
or clay soils. The design of ground anchors should be carried out by a competent person,
for example a geotechnical engineer.

In granular soil, the anchorage zone is usually a plug of grout located behind the active soil limit line. This plug resists the tension force induced in the stressing cables, due to the shear and cohesion forces developed along its length.

These forces can be due, in part, to the overburden. Removal of soil above installed ground anchors should only be carried out after approval has been received from a competent person.

Figure 18 Ground anchors for supporting steel sheet piling

Removal of the soil between the retaining wall