Document ID: chunk:federal_register_of_legislation:F2016L00416:reg:4:p18
Version: federal_register_of_legislation:F2016L00416
Segment Type: reg
Provision Reference: reg 4 (pt 18/21)
Character Range: 77091–79926

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 and the active soil limit line may cause sheet piling to bend. This bending will release the load in the stressing cable, and render the ground anchor useless and dangerous to workers in the excavation area.
The ground anchor may not develop its original load carrying capacity on replacement of the soil. The anchorage of the stressing cable at the face of the sheet piling may be also dislodged or loosened. This depends on the type of stressing cable and the respective anchoring systems. While the ground anchoring system is operative, periodic checks with hydraulic jacks and pressure gauges are used to assess anchor behaviour over long periods.

    6.3              Removal of shoring supports

Shoring and all support systems should be removed in a manner that protects workers from ground collapse, structural collapse or being struck by structural members. Before removal begins, temporary structural members may need to be installed to ensure worker safety.

When removing shoring, the support system should be extracted or dismantled in reverse
order to its installation. Persons performing the work in the excavation should not work outside the protection of the ground support system. No part of a ground support system should be removed until the trench is ready for final backfill and compaction.

    6.4              Shields and boxes

A shield is a structure, usually manufactured from steel, which is able to withstand the forces imposed by a ground collapse and protect workers within it. Shields can be permanently installed or portable and designed to move along as work progresses.
Many different shield system configurations are available for hire or purchase. Figure 19 shows
a typical trench shield.
Figure 19 Typical trench shield

Shields and boxes used in trenches are often referred to as trench shields or trench boxes,
and are designed and constructed to withstand the earth pressures of particular trench depths and ground types. They incorporate specific lifting points for installation and removal.
Trench shields and boxes differ from shoring as shoring is designed to prevent collapse where shielding and boxes are only designed to protect workers if a collapse occurs.

Trench shields and boxes are useful where other forms of support are not reasonably practicable to install. They are mainly used in open areas where access is available for an excavator or backhoe to lower and raise the boxes or shields into and out of a trench. They are generally not suitable where as access is difficult and ground conditions prevent the use of