Foundation proposals for 'problem' site

[valleyboy]

I am reviewing a site investigation report for a development.

The ground conditions at the site - firm boulder clay underlain by sandstone, mudstone, and inter-bedded coal seams. The coal seams will be investigated using rotary drilling to check rock head cover and presence of workings.

The SI report recommends conventional ground bearing foundations.

I am aware from a review of geological data held in my office that the site has been subject to landslip (now dormant).

I have a number of concerns:-

1 How will global stability of the structure be achieved if the landslip re-activates?

2 Will excavation at the toe of the landslip re-activate it?

3 The development is split level.What type of earth pressure should be adopted for the design of the retaining structures?

I will seek specialist geotechnical advice, but wondered if anyone has dealt with any sites with similar conditions.

VB

 

[fndn]

On 1) Engineering geologist should be involved to determine if the dips are adverse, neutral, out of plane etc. If they are adverse, you'll need a geotechnical to design a buttress or other stabilizing mechanisms.

On 2) The solution in 1) will incorporate this.

On 3) A bulk sample obtained from the mid hight section of the proposed wall should be tested for direct shear at "residual" strength and its in place unit weights determined. Equivalent fluid pressures may then be obtained from the above test results.

I would also ask the geotechnical engineer to approximate friction at the base and recommend minimum embedment depths at the appropriate foundation material.