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Geotechnical Interpretive Report

The consultancy is able to undertake many types of Geotechnical Interpretive Reporting and each one will be written with the individual projects requirements in mind.

All our Geotechnical Interpretive Reports will cover the following as a minimum and will often include further points in order to suit the project.

Discussion of any fieldwork and its findings
The expected and actual ground conditions encountered
Results and interpretation of any laboratory testing
Specific engineering recommendations for design
Discussion of solutions for any anticipated problems and
Recommendations towards any geotechnical special provisions

This report can be combined with a Contamination Assessment should they both be required.

Basement Impact Assessment

London Boroughs are implementing increasingly stringent requirements for planning applications for basement developments. Basement Impact Assessments (BIA’s) are becoming mandatory in the majority of London Boroughs. Chelmer provide a service that covers a BIA to meet these requirements and aim to follow the comprehensive guidance set out in Camden’s Planning Guidance for Basements and Lightwells (CPG4), July 2015. As required by the CPG4 Chelmer provide a BIA that includes:

  • Screening assessment of the main issues (primarily surface flow and flooding, land stability and groundwater flow)
  • Site specific ground investigation and site walk over
  • Desk study
  • Conceptual Site Model evaluating the implications of the proposed development
  • Ground Movement Analysis
  • Damage Category Assessment using the Burland Scale
  • Impact Assessment assessing all potential impacts and providing mitigation options where necessary

At each stage of the process an engineer with the relevant required qualifications will be involved in completing the assessment.

Bearing Pressure Report

In geotechnical engineering, bearing capacity is the capacity of soil to support the loads applied to the ground. The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil. Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure; allowable bearing capacity is the ultimate bearing capacity divided by a factor of safety. Sometimes, on soft soil sites, large settlements may occur under loaded foundations without actual shear failure occurring; in such cases, the allowable bearing capacity is based on the maximum allowable settlement.

There are three modes of failure that limit bearing capacity: general shear failure, local shear failure, and punching shear failure.

Slope Stability Analysis

This is undertaken to assess the safe design of both man-made and natural slopes and the equilibrium, conditions.

These can take into account slopes such as; embankments, road cuts, open-pit mining, excavations, landfills, river banks and railway cuttings.

Slope design required geological information and site characteristics and depends on both the site’s individual conditions and its potential for failure.

Settlement Analysis

Soils consolidate under the application of loads from buildings. The critical tolerances for total and differential settlement of large warehouse floor areas require detailed analysis and often involve innovative geotechnical engineering solutions, such as settlement reducing piles to minimise or control the long-term floor movement.

One of the common problems that we encounter is directional drilling or tunnelling operations which can cause ground movements that may affect existing surrounding buildings or structures including nearby roads or railways. In these circumstances we recommend that a suitable ground investigation is specified in order to predict these soil movements before the construction phase of the project commences.

Retaining Wall Design

A retaining wall is a structure designed and constructed to resist the lateral pressures of soil when there is a change in ground elevation that exceeds the angle of repose of the soil. Every retaining wall has to support a wedge of soil. The diagram shows a common retaining wall and the terminology used.

Plate Bearing Test

This test determines the bearing capacity of soils for allowable settlement under static loads at shallow depths.

The test is undertaken on a levelled surface or within a trial pit excavated to the anticipated foundation depth. The plate is increasingly loaded through a hydraulic jack and the settlements measured. The Settlement versus Bearing Pressure graph is then produced, showing whether the ground is suitable for the anticipated loads. The modulus of subgrade reaction, K, is then calculated.

California Bearing Ratio (CBR) Test

The CBR test is typically used for road design and concrete slab foundations. The compaction of the soil is compared to that of a standard material. A jack plunger approximately 50mm in diameter is penetrated into the soil and the forces recorded. The results are plotted and then compared to a standard curve for a value of 100% CBR.

Ground Movement Analysis

Ground movements can arise from two major sources: movements due to ground instability and movements due to a changing stress-state, leading to volume changes within the soil.

Of the two types, movements due to ground instability are potentially the most serious as they can lead to the collapse of a building. Movements due to changing soil volume tend to occur more gradually and normally result in damage rather than collapse. However, remedial measures such as underpinning and structural repair can be expensive for buildings subject to movement from either cause.

A thorough desk study is an important part of early feasibility work for new development.

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