Vibratory ground improvement techniques

4.5.12Verification of completed treatment

The engineer shall require the specialist contractor to verify that the ground treatment is satisfactory, including:

  1. suitable testing
  2. written confirmation of completed treatment
  3. recording of work.

Suitable testing

Tests should be carried out to establish the degree of ground improvement, the load-bearing characteristics and settlement potential.

The specialist contractor should:

  • predict the results from his experience of work on the type of ground prior to the test taking place
  • agree results and tolerance with the engineer prior to testing
  • agree results and tolerance with the engineer with actual results.

Where the results are vastly different, a further investigation may be necessary.

Where a threefold improvement were predicted and only a twofold improvement achieved, this could indicate that the ground was different to that identified in the investigation, or that the treatment carried out differed from the specified treatment.

Tests on ground containing clay soils may need to be conducted several days after completion to allow excess pore pressures to dissipate. The engineer may choose any appropriate combination of the tests detailed in Table 4, with the agreement of NHBC.

Table 4: Test methods

Table 4 (continued): Test methods

Written confirmation of completed treatment

On completion of the treatment, the engineer should:

  • use the test results to verify that the treated ground has achieved the anticipated condition assumed in the design
  • advise the builder and NHBC in writing of the verified effectiveness of treatment in relation to the design
  • advise the builder of any special precautions which should be taken for the positioning of services both beneath the home and adjacent to it.

Recording of work

A comprehensive record of all works should be made available to NHBC, including:

  • information concerning the treatment
  • depth of fill
  • volume of stone used
  • on-site changes
  • any other relevant information.