Ground Investigation for Road Improvement Schemes
Onyx Geo undertook ground investigations along multiple roads within a mixed-use development to inform a highway improvement scheme.
The works required careful planning and coordination to manage live traffic, with traffic management measures including lane closures and temporary traffic lights. The investigations identified variable ground and groundwater conditions within the underlying Bracklesham Group with variability in soil strength and California Bearing Ratio (CBR).
Objectives
· Assess the existing carriageway construction and underlying ground conditions.
· Investigate the groundwater levels across the sites.
· Determine the CBR of natural soils to inform pavement design.
· Chemical testing of the made ground to inform the risk to construction workers and a preliminary assessment of the likely waste classification.
· Testing to assess the presence of coal tar within existing road surface to guide appropriate disposal methods.
Scope of Work
Drilling: 80 road cores and windowless sampler boreholes to between 2.0 and 8.0 m depth.
Traffic management: comprising either lane closures, or traffic light control.
Sampling: Geotechnical samples collected to assess subgrade strength; environmental samples taken from soil and road surfacing materials.
Groundwater Monitoring: Installation of monitoring wells on roadside verges to track groundwater levels at monthly intervals throughout the winter.
Outcome
The projects were successfully delivered on schedule and under budget, providing data to inform pavement design, risk assessments, and compliant waste management strategies. The investigation supported the client’s wider development and infrastructure objectives with minimal traffic disruption
Site Investigation for a Commercial Unit
Background and Site History
A desk study revealed a complex site history. Originally open farmland intersected by a stream, which is now culverted, the stream was later dammed to form a Victorian boating lake, which remained until the mid-1970s. By the early 1980s, the site had been redeveloped to accommodate a warehouse, the same structure that remained until 2023. This history indicated potential ground challenges, particularly deep made ground resulting from historical backfilling of the former lake and potential alluvial deposits underlain by the Weald Clay Formation.
Site Investigation
Onyx Geo undertook a detailed intrusive ground investigation to assess the ground conditions and inform an appropriate foundation design. The investigation encountered soft alluvial silts and clays, extending to 4 m bgl. These soils were found to be unstable, with groundwater encountered at shallow depths across the site.
Given these conditions, traditional shallow foundations were unsuitable. Onyx Geo recommended a piled foundation solution for the proposed development.
Technical Approach
Dynamic sampling followed by rotary core drilling was undertaken to obtain high-quality geotechnical samples for laboratory analysis. The in-situ and laboratory testing results, combined with existing geotechnical data, were used to establish pile design parameters and provide preliminary pile resistance calculations to guide the structural design team.
Outcome
Onyx Geo’s comprehensive investigation and analysis enabled the client to move forward with a robust and sustainable foundation solution despite the site’s complex history.
Preliminary waste classification for offsite disposal
Overview
Onyx Geo was appointed to undertake an initial ground investigation and preliminary waste classification of an embankment at a site in West Sussex.
The purpose of the work was to:
- Inform early-stage cost estimates for excavation and disposal.
- Identify potentially hazardous waste streams.
- Reduce commercial and regulatory risk prior to construction
The assessment was undertaken in accordance with WM3 v2.1 Waste Classification – Guidance on the classification and assessment of waste, ensuring compliance with current UK waste legislation.
Objectives
- Develop an in-situ soil sampling plan based on the approximate excavation volumes and findings from previous site investigations.
- Excavate trial pits and collect representative soil samples for laboratory analysis.
- Undertake chemical testing.
- Prepare a preliminary waste classification and assessment report to support budgeting and programming.
Scope of Work
Ground investigation: excavation of approximately 14 trial pits to depths up to 2.30 m bgl; logging of soils following BS 5930; and the collection of representative environment samples for laboratory analysis.
Outcome
The project delivered a preliminary waste classification ofinsitu soils proposed to be excavated, with clear guidance on waste handling and disposal options. This allowed our client to reduce programme risks, identify disposal facilities at an early stage and comply with regulations.