GEOTECHNICAL SERVICES
Geotechnical Design
Geotechnical Design applies the fundamentals of soil and rock mechanics to civil engineering design and construction. AFHA provide a bespoke, site specific service when assessing the geotechnical requirements of proposed developments.
Every ground investigation is site specific and tailored to meet the engineering requirements of each project. The scope of works of the investigation will depend upon the anticipated ground conditions and the construction proposals.
A F Howland Associates provide extensive geotechnical services for and have extensive experience for development of buildings and structures from single houses to multi-storey offices and commercial/industrial structures.
Based on the findings of the site investigation and the requirements of the client details, recommendations and design options can be provided upon the following.
- Existing foundations – dimensions and composition
- Bearing capacity estimation
- Settlement analysis
- Design loadings for piled foundations
- Recommendations for conventional rafts or piled rafts
Subsidence Investigations and Analysis
Subsidence is a major cause of failure of structures due to excessive settlement of foundations. There can be a multitude of causal factors including:-
- instability due to the presence of naturally occurring voids or unmapped mine shafts or workings
- settlement and compaction of soils due to percolation of water
- groundwater level fluctuations
- variation in the moisture content of clay soils
As a result of being based in East Anglia, A F Howland Associates has gained extensive knowledge and experience of subsidence events and their investigations. Subsidence problems can arise from instability caused by voids in the underlying chalk created as a result of either historical mining or by the formation of natural solution/dissolution features in the chalk created by the erosional effect of surface and groundwater.
Another major cause of subsidence in the East Anglian region is shrinkage/heave movements caused by variations in moisture content of clay soils. Seasonal variation can lead to near surface movement but some species of trees can cause variations in moisture content to much greater depths through the action of their root systems.
Investigation of subsidence events utilise the following methods: -
- Exploratory holes (using cable percussive, window sampling or trial pitting methods) to identify features and obtain samples for laboratory analysis.
- Dynamic penetration testing to investigate relative soil resistivity
- Foundation inspection pits to determine foundation construction and depth
- Structural and vegetation surveys
Subsequently, recommendations can be formulated to advise upon the most cost efficient solution to the problem.
Road Pavement Design
In-Situ or laboratory CBR testing and dynamic cone penetration (DCP) testing can be utilised to allow design CBR values to be formulated so that subgrade surface modulus stiffness, E, can be calculated in accordance with TRRL – 1132. This allows efficient design of a variety of vehicular access and parking surfaces including public roadways, car parks and temporary surfaces for construction sites.
Litigation & Expert Advice
The experience in litigation of AF Howland includes formulating the contractual conditions and specification for term contracts for site investigations for the London Docklands Development Scheme. We engineered the innovative approach to provide a specific term contract for chemical/environmental investigations as well as one for traditional geotechnical investigations - believed to be the first of its kind.
Besides other major industrial activities in litigation, we have also acted for clients in the private sector involved in litigation over
- slope stability;
- foundation failures under the influence of adjacent vegetation;
- the migration of contamination from adjacent landfill sites;
- dewatering issues and failure of excavation support;
- adequacy of site investigation and the implications on tunnel and shaft construction;
- public enquiries on planning issues and compulsory purchase orders.
Contract Research & Development
We completed a Research and Development contract for the Environment Agency to evaluate the construction process of soil nailing for use in flood defence systems by the EA. This assessed the system, described the basic mechanics, and developed design guidelines for use by the EA engineers. The wider potential of the system was also described outside of those simply related to embankment stability. Finally the financial options available to the EA for use of the system were explored.
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