Pencoed, Bridgend
Introduction:
Identification of size and geometry of existing void caused by solution features beneath residential property.
Identification of areas potentially at risk from future solution features.
Remediation of solution cavity and soft ground conditions.
Details:
This was a project for the investigation and treatment of active Limestone Solution Cavity.
ESP were employed to undertake a Geotechnical Investigation at a residential development site in Pencoed. The assessment involved investigation of ground conditions surrounding a limestone solution feature which had expressed itself in the form of a large void (approximately 3m diameter and depth) beneath a conservatory; adjacent to the main structural foundations of a residential property.
Following a comprehensive desk-study including an assessment of aerial photography, both physical and geophysical investigation works were implemented. The site is a mid link terrace and access was restricted, therefore the use of a narrow Geotool rig able to perform dynamic probing, window sampling and SPTs was utilised.
The physical works allowed derivation of the conceptual site model, which identified variable depths to competent strata. Loose deposits were also encountered. A Geophysical survey utilising micro gravity techniques was carried out externally and internally. This provided good correlation of data between physical and geophysical methods and allowed an extension of the survey where intrusive physical methods could not be carried out. (i.e. inside the property).
ESP’s exploratory works were designed to establish, with confidence, the variable ground conditions across the site and identified the size and nature of the existing solution feature situated beneath the property.
A program of ground stabilisation was established by ESP which involved, back filling of the existing void by using a foamed concrete. This provided much needed stability to the existing ground by preventing any further ground collapse from the adjacent soil; further ground improvement was also required utilising compaction grouting.
Compaction grouting creates a series of high pressure grout bulbs, resulting in the lateral displacement and therefore compaction of the soil. This ground improvement will reduce loss of material by solution and therefore stabilise ground conditions.