Document ID: chunk:federal_register_of_legislation:F2016L00416:reg:4:p13
Version: federal_register_of_legislation:F2016L00416
Segment Type: reg
Provision Reference: reg 4 (pt 13/21)
Character Range: 64467–67242

is determined. Useful information can often be obtained from local authorities.
Non-cohesive faces can be very hazardous. With the right amount of moisture they can look safe and solid. A little loss of water by evaporation from the face or an increase in water content from rain or other causes can make the soil crumble.
The stability of any excavated face depends on the strength of the soil in the face being greater
at all times than the stresses it is subjected to. The following situations all increase soil stresses
in an excavated face and may lead to failure under adverse weather conditions, additional load
or vibration:

    * deep cuts and steep slopes, by removal of the natural side support of the excavated material
    * loads on the ground surface near the top of the face, such as excavated material, digging equipment or other construction plant and material
    * shock and vibration, which could be caused by pile-driving, blasting, passing loads or vibration producing plant
    * water pressure from ground water flow, which fills cracks in the soil, increases horizontal stresses and the possibility of undermining, and
    * saturation of soil, which increases the weight and in some cases the volume of the soil.
The following may reduce soil strength:
    * excess water pressure in sandy soil which may cause boils and saturate the soil and increase its plasticity
    * dryness of the soil may reduce cohesion in sandy soil and soils high in organic content which then crumble readily
    * prolonged stress, may cause plastic deformity (squeezing or flowing), and
    * prolonged inactivity at an excavation site. An evaluation of the soil should be undertaken before work recommences.
There are three main types of ground collapse control measures that can be used where ground collapse may occur:
    * benching and battering
    * positive ground support - for example shoring, and
    * shielding – shields do not ensure ground stability but they protect workers inside the shield from ground collapse by preventing the collapsing material from falling onto them.

    6.1              Benching and battering

One fairly simple way of controlling the risk of ground collapse is to bench or batter the excavation walls. An excavated slope is safe when the ground is stable. That is, the slope does not flatten when left for a considerable period, there is no movement of material down the slope and the toe
of the slope remains in the same place.
If excavation work is planned to be carried out without positive ground support (that is, shoring), the continuing safety of the excavation will depend on the conditions arising during construction.
If the conditions during construction are not as expected, or if conditions change during the