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A90/A937 Laurencekirk Junction Improvement Scheme

Tender Value: £308K
Client: Transport Scotland
Engineer: Amey

49

Rotary Holes 

Rotary drillholes were advanced through superficial and soild strata to obtain continuous cores of the materials encountered using geobore techniques. 

70

Trial Excavations

Trial pits were used to allow visualisation of the in-situ conditions and provide access for various geotechnical testing techniques.

30

In-situ Plate Load Tests

In conjunction with the trial pitting operation selected pits were used to carry out 600mm in-situ plate loading tests to establish equivalent CBR parameters for pavement design purposes.

12

Post Site Monitoring

Long-term post site monitoring was required over a period of 12 months to establish the groundwater and gas regime across the site.

PHASE INVESTIGATION SCOPE
Intrusive Site Work49 No. the drillholes employed soil coring using Geobore-S through a limited thickness of superficial cohesive strata (where necessary complemented by rotary percussive methods in granular horizons), followed by a  continuation of the same technique into the shallow underlying bedrock to a maximum depths of between 6 snd 20m depending on location within the scheme. In-situ SPT and hand shear vane testing was conducted where required by the specification. 

70 No. mechanically excavated trial pits were dug in order to obtain samples and provide visualisation of the in-situ conditions.

9 No. pavement core holes were used to recover specimens of bound carriageway layers to assess construction properties (including aggregate size, binder type, voiding). TRL dynamic probe penetrometer testing was additionally performed at the base of selected road cores to determine CBR parameters. 

30 No. 600mm plate load tests were undertaken in accordance with HD design standards to determine equivalent CBR value within the superficial layers in selected trial pits.
GeologyThe ground conditions within the location of the proposed link road related principally to thin glacial till (soils that were borderline in composition (fine grained cohesive) with subtle variations in their engineering behaviour and composition due to localised characteristics) over much of the site with patchy alluvium near water courses. These strata were underlain by solid regional geology related to Cromlix Mudstone Formation of Strathmore Group, (principally sandstone and sandy siltstones) evidently weathered intermittently at its upper interface.

The site was designated as GREEN (SISG) based on its known historical interactions (predominantly agricultural use) together with the published geology and prevailing succession revealed as the investigation progressed.
MiscellaneousDisturbed/undisturbed sampling techniques.
Apparent soil resistivity testing at designated points.
Field screening of selected environmental soil samples using PID methods to determine SVOC/VOC levels.
Variable head permeability testing.
On-site groundwater and surface water sampling including in-situ environmental parameters.  
Accurate Surveying of all investigation positions.
Pre and post land condition surveys.
Post Site Work MonitoringThe contract included 12 No. scheduled visits after the completion of the site work. 

Groundwater and gas monitoring (where specified) in 40+ No. installations - essentially all new instrumentation installed during the contract.

GENERAL

The planned improvement scheme comprises a new grade-separated junction layout at the southern intersection of the A937 over the existing A90 bypass in the vicinity of Laurencekirk. This will aim to alleviate traffic congestion and vehicular incidents. The A937 provides a single laned route between Laurencekirk and Montrose, whilst the A90 is a dual carriageway which serves as the main strategic link on the eastern periphery between Dundee and Aberdeen. The intended proposal will involve the realignment of the A937 that will incorporate sections of new highway, slip roads and roundabouts and widening of existing carriageway lanes. The proposed link road is impinged by several existing salient features that range from road and railway structures to culverts, cuttings and embankments.

Amey were nominated in the role of Investigation Supervisor for this phase of the design process and were present on site throughout the intrusive phase of work.

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. Landowners were liaised with to approve access ways and a pre-condition survey was also undertaken in advance of the intrusive works. 

All operations on or to the immediate side of the live carriageway network were facilitated by traffic management within an agreed duration of the works notifiable with BEAR Scotland (NE) and Aberdeenshire council. The siteworks were performed to a strict protocol under the company’s certified integrated management system to ensure relevant health & safety, environmental and quality objectives were met in line with the Investigation Supervisors requirements.  

LAND USE

The site was predominantly farmland (arable); at the time of the investigation most fields in which intrusive work was required were cropped. Certain areas of the site had greater sensitivity particularly those exploratory holes located in close proximity to Gaugers Burn towards the eastern extent of the investigation area.

INVESTIGATION HIGHLIGHTS

All siteworks were completed in accordance with the Investigation Supervisors objectives. 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. groundwater management, sloped access. 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. 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 the concentration was 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 investigation finally being issued in a digital AGS compliant format.