Foundations and Floor Slabs

An Introduction to Foundations and Floor Slabs

 

​​​​In order to provide information that can be used to determine geotechnical design parameters for foundations, floor slabs and pavements, a Site Investigation is required.  The geotechnical ground investigation report for a proposed development will typically include advice regarding the following:

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• Anticipated minimum foundation depths based on factors including the presence of Made Ground and other unsuitable strata, the type(s) of suitable founding strata present, including their volume change potential and strength, the types and proximity of trees present, the presence of otherwise of groundwater, and the details of any proposed development;

• Recommended foundation types, e.g. trench-fill, shallow strip, reinforced strip on engineered fill, pads, piles; these foundation types can take various forms such as foundation slabs, strip foundations, and point foundations.

• ​Likely allowable bearing pressures at the anticipated founding depths;

• Recommended ground floor slab types, including any need for heave protection and gas protection measures. Recommendations may include 'beam-and-block' type suspended floors, cast insitu suspended floors, ground bearing floor slabs etc. Recommendations are likely to dependant on factors such as the ground strength, the thickness of unsuitable strata such as Made Ground or soft Alluvium, and the influence of trees, as well and anticipated loadings on the proposed floor slabs.

• Recommendations for ground improvement works to allow the use of ground-bearing floors slabs if they are necessary for proposed commercial or industrial building at locations where the existing ground conditions are not suitable; this may include techniques including traditional earthworks, lime stabilisation, soil-mixing, vibro-replacement columns and similar

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​How Can G&J Help with Your Foundation and Floor Slab Designs?

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​​​​​​In addition to the above ‘foundation report’, we can also provide the following for proposed developments:

• Foundation zone plans to show where on a site different types of foundation (e.g. strip, trench-fill or piles) may be required;

• Tree influence drawings (subject to the provision of a topographical survey and suitable tree survey, both of which can be arranged by G&J if needed) to show where proposed foundations will need to be deepened;​

• Targeted ground investigations and soil desiccation assessments, especially in areas where the tree influence suggests that foundations deeper than 2.5m may be required. Such an assessment may show that excessively deepened or piled foundations are not necessary.

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​What About Subsidence?

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If an existing structure is showing possible signs of subsidence, let us know and we can assess the potential causes (probably initially involving a site visit and some 'desktop' research) and then, if considered necessary, carry out an appropriate ground investigation to allow for suitable and cost-effective remedial works to be arranged. Possible causes of subsidence can include the effects of tree influence, shrinking/swelling clays, inadequate foundations for the underlying ground conditions, the presence of soft or variable strata, and the presence of mine workings or other geohazards.​