Solution Features in Chalk

Project

Lankelma carried out a site investigation for the identification of solution or dissolution features within chalk. The tests were performed for one of the UK�s leading PFI contractors at a site in Hertfordshire.

Tests

29 tests were performed to depths of up to 21.54m below ground level. They were taken through very stiff and up to very dense superficial deposits and into the underlying upper chalk up slightly/unweathered (Munford Grade 2).

Gamma profiles

The gamma profiles were used to assist in the estimation of Chalk Grade Classification, defined by Wakeling et. Al. (1968) and Wakeling (1969) and a modified correlation originally derived by Power (1982).

Gamma cone system

The site investigation consisted of cone penetration testing using our newly updated and modular natural gamma cone system. The system accurately defines the depth and sequence of sediments in a solution feature, typically showing a relatively high gamma response within superficial soils and a very low response in chalk.

The system is modular, with the gamma element being mounted behind a conventional 15cm2 friction (CF) cone or piezocone. Therefore geotechnical data (cone end resistance, sleeve friction and porewater pressure) is obtained simultaneously with a constant measure of natural gamma data in the same test.

Results

The speed, volume and quality of information is unrivalled in the site investigation industry compared to conventional drilling methods.

The test results can be used pre-piling operations, as an improved ground model and understanding of underlying ground conditions can be achieved. This reduces pile installation risks and optimises the pile design.