The planned improvement scheme encompassed both north and southbound carriageways of the A19, between the A1027 Norton Junction and the existing link road to the A689, some 1.5 kilometres north of the A689 Wynyard Junction. Over this corridor of crucial road infrastructure the A19 represents a busy dual carriageway, administered by Autolink Concessionaries Limited (Autolink) for Highways England. This section of the A19 is crossed by a number of existing structures which range from road and rail bridges to culverts and underpasses, the latter for agricultural access and use. WSP (Newcastle) were nominated in the role of Investigation Supervisor and were present on site throughout the intrusive phase of the work.
The main scope of the investigation is provided below:
42 No. light cable percussion boreholes
42 No. windowless sample holes
23 No. hand excavated service inspection pits
15 No. vacuum excavated service inspection pits
14 No. shallow trial pits for insitu testing requirements (i.e. CBRs)
In addition to the above the Company commissioned a detailed underground services survey and mapping exercise and retained the services of UXO specialists, the latter to confirm the absence of unexploded WWII ordnance which was considered to be a plausible risk to the intrusive operations. Post-site activities included long-term monitoring of the groundwater conditions corresponding to the instrumentation emplaced in completed exploratory holes. All works on or to the immediate side of the A19 were facilitated by traffic management within an agreed working duration.
The ground conditions related principally to Glacial Till (e.g. firm to stiff slightly sandy slightly gravelly CLAY) over much of the site with patchy near surface Alluvium (e.g. organic CLAY, or PEAT) and Glaciolacustrine (e.g soft or firm laminated CLAY) deposits. Sand and gravel strata were also reported in certain areas of the improvement section towards the base of the superficial sequence. The solid geology related to Roxby Formation, formerly referred to as the Permian Upper Marls, with the Sherwood Sandstone Group also featuring in proximity to the Norton and Billingham junctions.
All sitework was completed in accordance with the Investigation Supervisors objectives, which included an additional variation contract to the main scope. The variation works encompassed carrying out around fifteen carriageway cores to inspect and photograph the existing pavement construction at various points within the improvement section. This additional work was undertaken using the company's trailer mounted diamond coring rig, Xcalibre. In accordance with any work on roads the pavement construction was fully reinstated after completion, or temporarily reinstated between shifts where investigation requirements were incomplete.
The main difficulties experienced during the investigation operations were addressed by a strong management lead, thereby ensuring smooth integration between the day and night-time teams, effectively a focus on good levels of information interchange to avoid issues that arose during one shift affecting the next. As a proportion of the works were on neighbouring agricultural land, which included soft surface conditions, the weather was also a crucial factor with respect to plant movement operations and this included efforts to minimise damage - yielding at least one novel solution. There were also occasions where nightshifts were cancelled or cut-short as a consequence of poor weather conditions by Autolink. In such cases the decision making process considered operator safety first without compromise and communications between all stakeholders involved in the project was a key factor. The rapport that was established between Autolink, WSP and the company was extremely productive and was instrumental to achieving the site technical objectives. From our perspective this was one of the high points of the contract.
After completion of the site phase of the investigation the focus transferred into our UKAS accredited laboratory which was then tasked with meeting the specified soil testing requirements. Geoenvironmental samples were administered during site by the company, however, determinant testing was carried out by DETS (Consett) under a sub-contract agreement. Geotechnical testing ranged from routine classification, through to earthwork suitability and also encompassed more complex procedures which were undertaken in our specialist testing facility (i.e. shear box, effective stress). Throughout this phase we concentrate on quality, accuracy and data integrity, which is underpinned by our robust quality management system. The same is also true in relation to the report preparation phase and the iterative system we have in place to fully quality check submissions to client organisations. All data acquired during the course of the investigation finally being issued in a digital AGS compliant format.