Posted By Bob Shillabeer
Hi, the answer to your question is where any excavation is deeper than 1.2 m deep where there is a risk of material collapsing or falling, proper timbering, trench sheeting etc, must be used to safeguard operatives as per Regulation 8 of the Construction (General Provision) Regulations 1961. However, these Regulations are withdrawn upon the coming into force of the new CDM Regulations. Section 31 of the new CDM Regs states that all practicable steps shall be taken to prevent danger to any person, including where necessary, the provision of supports or battering to ensure that any excavation or part of an excavation does not collapse, that no material from a side or roof of or adjacent to, any excavation is dislodged or falls and no person is buried or trapped in an excavation by material which is dislodged or falls. The Regs also state that suitable and sufficient steps be taken to prevent persons, work equipment or any accumulation of material from falling into any excavation.

It is worth remembering that the requirements of the defunct Regulations may still be quoted as good practice unless a better method is introduced, therefore it may be a good idea to get a copy of the old the Regs for reference purposes. Note that Reg33 (1) provides for new duties in relation to inspections of excavations.

Hope this helps.

Bob.

Posted By Simon Carrier
Thank you both for your replies, very useful.

regards

Simon

Posted By Ciaran McAleenan
Simon

The requirements Bob quoted were revoked with the 1996 Construction Regulations. The requirements stated as new in CDM07 are those that have been in place since 1996 (including the need to inspect).

The 1996 Regs refer to excavations that are in a temporary state of weakness or instability. Not deep.

While 1.2m might still be a good rule of thumb Lilian's comment points correctly to circumstances that could justify the need for support at lesser depths. i.e. "in a temporary state of weakness..."

Regards

Ciaran

Posted By Andrea Kay
Could anyone out there give me an opinion on the following scenario:

A team (2-3) of land quality people are required as part of a survey to assess the level of contamination in trial pits. This involves standing at the end of the pit, looking into and measuring the depth of the pit.
The trial pits are approx 1.25-2.0 metres deep and are unguarded. The ground can obviously be unstable, due to its past history or merely due to weather conditions.
Those carrying out the survey feel it is impractical to put barriers in place, since pits usually covered over at the end of the day.
Have previously tried the laser type tape measure, not accurate enough. Anyone have any ideas re control measures?. Obviously concerned about the unguarded drop.
Job currently on hold until a solution can be found...

Posted By Jo Thomas
This is a brief “off the top of my head” for trial pitting, not a RA ;)

Have a look at

BS5930 British Standard Code of Practice for Site Investigation 1999
BS10175 British Standard Code of Practice for the Investigation of Potentially Contaminated Sites, 2001

Only measure from the short end of the trial pit (I've usually used a 0.60m bucket on most phase II investigations). Long wall is more unstable, I generally avoid going to close.
If sides unstable, don't measure, estimate and mark in logs that sides were unstable.

Visually assess side stability as pit is excavated. I'm assuming they'll be looging to BS5930, so the pit won't be excavated all at once, rather in stages.

Only take contaminated samples from the digger bucket once it’s resting on the ground well to the side of the pit - tell the operator to get you a sample from the stratum/layer you’re interested in.

Climbing on the spoil mound for samples is not recommended.

In terms of barriers, on closed or derelict sites, I've never used them, but with the caveat that should anyone come over to talk to me or during a break in activity (say lunch) that the digger bucket/arm is placed in the hole (if it can't be backfilled immediately)

On school sites or open commercial ones, we usually try not to use trial pitting, and go for a drilling method instead (reduces risk as no gaping holes). Talk to site staff and arrange for staff to be briefed on works being undertaken and location.

Either way, pitting or drilling, temporary barriers similar to the ones used by the utilities round their trenches are usually good enough, just remember to locate them round the hole, *and* round the other end of the digger, giving enough space for the guys to operate safely, and keeping the public etc away.

I’m assuming you’re all sussed with regard to handling the contamination aspect.

Are you using a geotechnical/environmental contractor or doing it yourselves?

Posted By Richard Patrick George
Hi, Simon. You should consider deeper than 1.2mtrs as deep trench. Secondly deep trench should have proper sloping and benching so that any material slides down the slope shall rest on the benching and the benching should be wide enough to accumulate the falling material. If the area is of loose sand, then it has to be watered and battered regularly from collapsing