2. SAFETY

2.1 General


No excavated ground can be assumed to be safe and all ground can collapse without warning. The conditions likely to be met in excavations will vary widely. These notes cannot, therefore, be entirely specific in relation to the support of excavations, but guidance is given as to when expert advice should be sought. These notes only relate to excavations utilising open cut or temporary support methods. Specialised methods such as diaphragm walls, bored pile walls and ground stabilisation by injection, freezing and dewatering are excluded; as their use must always relate to designed conditions and/or specialist advice.

The support of excavations divides into two categories:

(a) Where so-called standard solutions are used:

(i) Battered side (open cut) excavation.

(ii) Standard details from BS

(iii) Proprietary systems.

(b) Purpose designed for the particular situation by persons competent to do so.

Where any doubt exists, always seek advice from your local Health and Safety Advisor.

2.2 Requirements

It is mandatory for a competent person to be made responsible for the supervision of excavation under the general direction of the Agent or other person having overall responsibility for the contract. This applies whether standard or designed solutions are used.

The management team of any project involving excavations deeper than 1.2m should include the necessary requirements in their Company Standing

Instructions/Procedures.

Such requirements usually include the following:

(a)   All excavations exceeding 1.2m deep, must be supported or excavated to a safe batter.

(b)   All excavations exceeding 1.2m, if intended to be left unattended, must be protected by a rigid barrier not less than 1m in height - or be covered by robust material.

(c)   Provide safe means of access into excavations.

(d)   Provide barriers or stop blocks where cranes, dumpers, lorries, etc., are required to manoeuvre close to the edge of the excavation.

(e)   Excavations must be inspected by a competent person daily or at the beginning of each shift. In addition, this person must carry out and record the results of thorough examinations at least every seven days or after the use of explosives or where an unexpected fall of rock, earth or other material has occurred likely to have affected the stability of the timbering or other supports.

(f)   Adequate supplies of timbering and propping materials of a suitable quality must always be available and to hand before excavation starts.

2.3 Standard solutions


(a) The use of standard solutions should only be applied in the following circumstances:

(i) Double sided, narrow trench support, not exceeding 4m deep, in dry ground.

(ii) Shallow pits, not exceeding 4m deep.

(iii) Where water problems have been eliminated by other means, e.g. well pointing, but within the limitations of (i) and (ii) above.

(b) When deciding the slope (or batter) of open cut excavations, proper account must be taken of the material in which the excavation will take place.

(c) Do not assume that excavation in rock is necessarily stable

(d) Where support (timber, trench sheeting, etc.), is to be used recognised good practice must be followed in detail.

 e) Installation of support must maintain safe conditions at all times.

(f) Where proprietary systems are adopted, installation must be strictly in accordance with manufacturers' instructions.

(g) All decisions in relation to the foregoing must be determined by the person on site responsible for ground works, under the direction of the Site Agent or other persons responsible for the contract as a whole.

    (h) Persons erecting or removing the supports must always work within the protection of some form of existing support or from outside the excavation, and be under immediate supervision.

    (i) The system of work to be adopted must be explained in detail to all persons engaged in placing or removing supports, and others who will be working in the excavation. Written work instruction must be provided if safe working cannot be maintained without them.

    (j) The method of work and instructions given must be strictly adhered to. If doubt arises the nominated competent person must be consulted.