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HOLBORN ENABLING WORKS

Tender Value: £470K
Client: South Tyneside Council
Engineer: Mott MacDonald (Newcastle)

30

On-Land & Overwater Combined Cable Percussion & Rotary Holes

Cable percussion boreholes were used to categorise the superficial deposits as well as to facilitate sampling and insitu testing throughout the riverside sequence; this included most boreholes being extended using rotary coring techniques.

73

Trial Excavations (Structural, Geotechnical and environmental)

Various types of trial pits were excavated to predominantly expose and establish dockside structures and areas of potential contamination. These were both extended by hand and mechanical techniques.

30

Concrete Horizontal Wall Cores

A large number of horizontal wall cores were carried out to determine the structural make-up of dockside retaining structures.

1

Bespoke Information Solution

It was imperitive to provide up-to-date information on the progress of the investigation on a daily basis. A bespoke on-line system was put in place to facilitate the tracking of the investigation.


The investigation area was divided into two principal sub-sites known as Windmill Hill and Holborn Lower Levels.

Windmill Hill: This section of the site comprises an area of approximately 1.42 ha located to the immediate east of the former West Docks and south of the Holborn, on the eastern bank of the River Tyne. The Site was undeveloped and comprised managed open green space with occasional trees and shrubs. 

Lower Levels: The Lower Levels (also referred to as Middle Docks) comprised approximately 4.2 ha of land located on the eastern bank of the River Tyne Estuary, aligned north-east to south-west along this particular section of the river. Historically the site housed the ‘Middle Docks’, a disused ship repair yard formerly operated by the Tyne Dock Engineering Company and Cammell Laird, containing four large former graving (dry) docks. All Middle Docks buildings had been demolished and infrastructure (such as cranes) removed since its closure in 1999, except for the Old Dock Master’s Office building. In general, the majority of the site was derelict and predominantly covered by concrete hardstanding with piles of demolition waste and historic foundations pertaining to former buildings/structures. Relic basements and pits still remained on site at several locations. Timber jetties were present along the south western dock boundary, in various states of repair. A suspended reinforced concrete quay structure was present along the northwestern dock boundary supported on two sheet pile quay wall structures.

Both site areas had seen significant historical industrial activity with contamination residues likely as a consequence. Accordingly, the Holborn Lower Level and Windmill Hill area were classified as RED. The area surrounding the site was also known to have been bombed during the Second World War (WWII) and therefore a UXO briefing with associated magnetometer cover was in-place for certain operations. The initial pre-contract stage involved ensuring that all  health and safety information was in place, with Allied Exploration assuming the role of Principal Contractor for the scheme. Detailed Risk Assessments and Method Statements were developed, including a detailed plan illustrating the sequence of the works. This included engaging the local community in the Windmill Hill area of the site, by preparing an information package with respect to the works and the degree of impact it might have on the immediate neighbourhood residents. A pre-condition survey was also undertaken in advance of the intrusive works.

The main scope of investigation is provided below (encompassing both areas of the site):

BOREHOLES
23 No. light cable percussion boreholes, the majority with rotary coring continuation into the underlying Middle Coal Measures bedrock. 2 No. cable percussion boreholes with rotary coring continuation through an existing suspended quay. 5 No. over-water boreholes with rotary coring continuation along the quay-edge. The Company actively engaged with the Port of Tyne Authority (Harbour Master) with respect to the over-water investigations works which were carried out using a floating platform approach stabilised with spud-legs and anchors due to the tidal locality. Safety was a key consideration during the over-water works and welfare resources were such to address the assessed hazards. This included operator survival training and overboard recovery techniques. In addition, selected on-land holes were undertaken using a dynamic sampling approach employing a small (lighter) tracked rotary rig.

TRIAL PITS or TRENCHES
73 No. mechanical or hand excavated trial pits and trenches. There was a wide technical brief for the trial pits which were scheduled to address specific areas of potential contamination, to establish the structure and supporting elements connected to the retaining walls as well as various geotechnical requirements. This involved reviewing historic drawings of the quay construction to establish the most appropriate location to excavate trial pits to access anchor blocks and avoid supporting tie-rods. 

WINDOW SAMPLING 
10 No. windowless sample holes using a small tracked mini-rig which was deployed predominantly for potentially contaminated areas where continuous recovery of in-ground soils was required.

WALL CORES
30 No. horizontal or inclined concrete cores undertaken at various elevations relative to specified retaining structures in order to provide information on structural issues and construction.

ASSOCIATED ACTIVITIES
In-situ testing and disturbed/undisturbed sampling techniques.
Sampling and PAK testing of macadam hardstanding access routes.
Dock sediment sample recovery.
Field screening of all environmental soil samples using PID methods to determine VOC levels.
Continuous tidal monitoring using Diver data-loggers placed in installation and open-water.
On-site groundwater and surface water sampling.
Post-works groundwater and gas monitoring in new and existing installations.
UXO mitigation.

All sitework was completed in accordance with the Investigation Supervisor's objectives and encompassed by our quality management systems.

The main difficulties experienced during the investigation operations were addressed by a strong management lead, thereby ensuring smooth integration between all operations which were occurring concurrently on-site. Access, in the most part, was not a significant issue although certain areas of the site had specific hazards that influenced plant movements, i.e. known basement areas. Steps were taken to avoid cross-contamination between investigation points and a site compound was set-up as a focal point to manage all daily activities. A bespoke information system was put in place to facilitate continuous progress reports from site and enhance the submission speed of technical information. Trackers were initialised to allow the Investigation Supervisor to assess the status of the investigation throughout the operations. Specific data that was tracked included the collection and testing of contamination samples, geotechnical testing, general hole-by-hole investigation progress and the status of the reported elements pertaining to the investigation points. This was a new implementation for the Company and as such, due to its success in connection with this project, will be developed further. The process assisted in achieving a relatively tight contractual site period to the satisfaction of the Investigation Supervisor. 

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 the site works by the company, however, determinant testing was carried out under a sub-contract agreement. 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.