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A9 BERRIEDALE BRAES IMPROVEMENTS (INC. DIALOGUE WORKS)

Tender Value: £400K
Client: Transport Scotland
Engineer: AECOM (Glasgow)

17

Drillholes

Drillholes were advanced through characteristically resilient sandstone, siltstone and mudstone deposits using a fast rotation thin-triple tube barrel approach. High levels of rock recovery were maintained at all times.

8

Duration

It was originally intended to work towards a 3 week contract period, however, set-backs as a consequence of the weather extended the site works into a fourth. 

12

Geotechnical Trial Pits

Mainly used to assess the near surface superficial deposits, collect sufficient bulk samples of the rock and to conduct in-situ testing procedures. 

2

Access Solutions

As a good proportion of the investigation was undertaken on a steep sea facing slope access routes (for tracked plant) had to be constructed in advance and later fully restored.


SUPPLEMENTARY WORKS

Berriedale Braes is situated only a handful of miles south of Wick in the Caithness region of Scotland; in fact it is the furthest north the Company has undertaken contract work with this opportunity being provided by Transport Scotland. The A9 trunk road (at the time of the award) was subject to a major programme of infrastructure investment, with the series of bends at Berriedale Braes receiving attention. It is a potentially dangerous section of highway, especially the tight hairpin bend in the northern approach/exit which is also relatively steeply inclined making it treacherous in icy conditions for long vehicles.

Our commission was supplementary to further similar works undertaken by others, such as URS/Scott Wilson (2011) and BAM Richies (2013, 2014), the latter responsible for the main investigation phases. The improvement of the main hairpin section has been in the public domain for a number of years and consequently has received a fair amount of media focus.

The investigation supervisor was AECOM (Glasgow) and although we had collaborated with this office on a previous occasion, albeit some years previously as URS, it was good to reacquaint our presence once again. Scheduled intrusive works included an original nine rotary drillholes (openhole and rotary) with or without dynamic sampling through the superficial deposits and five machine excavated trial pits. These techniques were combined with sampling and various insitu testing procedures, as well as gas/groundwater instrumentation requirements in completed drillholes. Other highlights of the investigation included the selected use of optical/acoustic televiewer (provided by European Geophysics) in order to assess down-hole rock mass conditions drilled in areas of cutting along the proposed improvement route, as well as a heavy reliance on monitoring existing (previously installed) and newly installed monitoring instrumentation. The monitoring requirement continued after completion of the site work with six post-site visits over a circa three month duration.

On paper the contract appeared to be fairly routine, however, our judgement did not take into account the potential impact of extreme weather conditions during the December 2017/January 2018 period when the investigation works were undertaken. Extreme weather was the very factor that created the most difficulties on site, particularly in connection with access routes, which in part required significant earthworks to negotiate the relatively steep sea-facing slope in proximity to the hair-pin bend. Prior to commencing the works surface conditions were at this time 'the worse ever seen' in accordance with landowner comments and these transferred directly into challenges to be addressed. The advent of Storm Caroline during the first week contributed to the scene, followed by freezing weather with weekly outbreaks of snow and daily heavy rainfall leading into the Christmas hiatus. Site plant was configured to suit the terrain and access conditions, with sloped positions using all tracked plant including the compressor unit. A tracked excavator was used to excavate and later reinstate all routes, this included areas that were outside the immediate drilling locations to ensure that the landowner was completely satisfied by our duty of care.

Some inevitable delays occurred, but work continued throughout due to our very resilient site team and on-site management regardless of the weather in order to meet the contract deadline. The situation proved that as a company we could pull together and this process was assisted by the support of the local community. The investigation was concluded shortly into January 2018, a little longer than expected, but nevertheless achieving the contract deadline. Over much of this period the site team worked through weekends in order to maximise productivity as a consequence of the short days and weather issues. A second tracked rotary rig was mobilised to facilitate the televiewer early in the New Year, thereby allowing previously drilled holes to be cleaned-out and completed with an installation.

Beside the challenging site work experience, the laboratory work was undertaken in-house with certain elements outsourced to other UKAS accredited facilities. The final report was prepared in early April 2018 with the dataset acquired from the investigation supplied in both AGS 3 and AGS 4 formats in accordance with the specification. Overall it was a learning experience for us, as well as one that will almost certainly have a positive influence on projects of a similar technical status and scope. The importance of the weather, especially in Caithness during the winter, seemingly conspiring to do its worse at every stage of the investigation process, being a critical factor that will not be underestimated in the future.

DIALOGUE INVESTIGATION WORKS 

An additional phase of investigation works was commissioned by Transport Scotland in relation to suggestions put forward by the Main Contractors during the tendering phase for the construction of the improvement scheme. This second package of investigation was substantially larger than the Supplementary Phase and included additional drilling and trial pitting techniques. However, these intrusive operations were complimented by pavement coring along the A9 Trunk Road with associated TRL-DCP, seismic and resistivity non-intrusive surveys (in areas of cutting for rock rippability information and continuous profiling of the bedrock contours) and geological scan-line logging techniques along a section of rock outcrop. The investigation involved close liaison with various parties and regulators with a much greater focus on the local ecology as a consequence of the seasonal difference from our previous visit. From a Company perspective there is particular thanks to BEAR Scotland, ALBA, GOW Plant Hire, TerraDat and European Geophysics for their support throughout the works. 

Whereas the Supplementary Investigation was undertaken in what seemed a constant downpour of rain, snow and sleet for all but a handful of days during the site period, the Dialogue Works enjoyed the best weather that Scotland had to offer. In the glorious surroundings summarised by the east coast of Caithness, the site team enjoyed the experience and local hospitality.

The works were undertaken from May 2018 to early June 2018, with all the intrusive operations concluding within a three week period. Non-intrusive operations were contained to the fourth week to ensure the best data collection resolution possible for the seismic and resistivity techniques used, which included preventing any potential influence from drilling.

In accordance with the Supplementary Works there was a similar amount of laboratory testing and a high degree of effort to make the report a product of excellence as well as providing added value to Transport Scotland's specified requirements.