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Aberdeen gets on the fast track for a bypass

After 10 years of legal issues, work on Aberdeen’s new western bypass got underway at the start of this year with ground investigations starting on site - even heavy snow hasn’t held the work up this time.

Weathering_the_storm

Despite snowfall on 12 consecutive days, the ground investigation continued

The Aberdeen Western Peripheral Route has been in development since 2003 and is a major infrastructure project that will improve travel in and around Aberdeen and north east Scotland. The new route will also bringing economic, environmental and road safety benefits to the area.

From the outset the £650M dual carriageway route has been blighted by a series of legal challenges but, on 17 October 2012, the Supreme Court ruled that the scheme could go ahead.

The road is a priority for the Scottish government and is being developed by Transport Scotland, in partnership with Aberdeen City Council and Aberdeenshire Council.

The decision by the Supreme Court was welcomed by Scotland first minister Alex Salmond. “Work will now proceed apace,” he said. And true to this, transport minister Keith Brown kicked off the final phase of ground investigations for the route just before Christmas when the £1M contract for the ground investigation final phase was awarded to Soil Engineering Geoservices.

This round of investigation marks Soil Engineering’s fourth visit to Aberdeen, with previous investigations undertaken in 2004, 2006 and 2008.

Core_boxing

Mud drilling techniques were used to maximise core recovery

Work on site started in mid-December and were programmed a finish as this issue of GE went to press. The investigation stretches the entire length of the proposed 48km route from Blackdog in north east Aberdeen to Kingwells and then Cleanhill in south west Aberdeen and then onto Charleston in south east Aberdeen, with a fastlink spur from Cleanhill to Stonehaven.

The current works are aimed at filling gaps in the geotechnical model developed from the previous investigations where land could not be accessed, or where further information was required.

According to Soil Engineering, the nature of this final phase of work meant that each exploratory hole came with its own challenges - not least that of the weather.

“Solid geology encountered has predominantly been granite and schist with some gneiss with the granite presenting the most problems due to its high strength.”

Following an exceptionally wet summer, autumn and early winter last year, most of the site has been saturated and moving equipment has proved one of the major challenges for the site team. Two tractors have been on site to ensure plant and equipment can be safely repositioned between exploratory holes without causing excessive damage.

In addition to the waterlogged ground, snow fell continuously for 12 days, which added to the challenge of moving from one position to another, but work continued throughout.

Many sections of the route also have ecological or archaeological constraints and Soil Engineering has employed an ecological clerk of works and an archaeological clerk of works full time on site.

Ecological issues that had to be overcome include working closely to the habitats of badgers, bats, otters, voles and red squirrels. A handful of boreholes located in areas designated as Sites of Special Scientific Interest.

 

Bypass benefits

The Aberdeen Western Peripheral Route is expected to generate 14,000 jobs and around £6bn investment in north-east Scotland over the next 30 years.

“I’m delighted to see that work is getting under way so quickly. It’s a huge encouragement for the people of the north-east to see things start moving,” said Aberdeen City Council leader Councillor Barney Crockett. “A lot of preparatory work has to be carried out before construction can begin, but I think we can all take this as a good sign that we are on the way to realising our ambition to have a greatly improved infrastructure system.”

Leader of Aberdeenshire Council Jim Gifford added: “After many years of debate and delay, I’m delighted to see work starting on the AWPR.

“This is one of the most significant infrastructure projects in the UK at this time and I’m pleased to see that agencies have wasted no time in making a start on the investigation works.”

The geology of the site also presented its own difficulties. Superficial deposits across site are predominantly glacial with localised peat, river terrace and alluvial fan deposits close to water courses. The glacial deposits are mainly granular and in places particularly course - boulders can be in excess of 5m3 - and as a consequence, a minimum cable percussive boring diameter of 200mm has been used.

Solid geology encountered has predominantly been granite and schist with some gneiss with the granite presenting the most problems due to its high strength. In places pegmatites have been encountered. These have been exceptionally hard with rotary core progress slowing to as little as 100mm per hour.

The highly fractured nature of the schists has led to difficulties in recovery. However, drawing on previous experience of the site, Soil Engineering has applied mud drilling techniques to maximise recovery in areas where there was known to be a problem on previous investigations.

“Snow fell continuously for 12 days, which added to the challenge of moving from one position to another, but work continued throughout.”

At other locations, air/mist, water and foam flushes have been used to ensure recovery did not fall below 90% in any core run. Triple tube T6116 core barrels are being successfully used with diamond impregnated core bits.

For consistency with previous investigations along the route, all logging is being done in accordance with BS5930 (1999).

The scope of work at the site includes 50 cable percussive boreholes, 60 rotary cored boreholes, 27 sonic drilled boreholes, 120 trial pits with insitu soakaway, CBR and MCV testing and 20 optical or acoustic televiewer surveys. Pavement investigations included pavement cores, FWD testing and GPR surveys.

Most of the boreholes incorporate monitoring equipment to enable long term monitoring of groundwater and gas over the next 12 months. This will be undertaken in conjunction with monitoring existing groundwater and gas installations from previous works.

Samples obtained during the investigation will undergo geotechnical soil and rock testing at Soil Engineering’s in-house testing facility in Leeds, while the environmental testing has been subcontracted to SAL.

The findings of this investigation will give potential bidders the information they need to submit their tenders for the main works contract which will be issued in spring.

The AWPR scheme will be taken forward under a Non-Profit Distributing (NPD) model for of contract to ensure value for money. It is expected that construction of the route will commence in 2014 and the route will be open to traffic in 2018.

“Most of the boreholes incorporate monitoring equipment to enable the long term monitoring of groundwater and gas over the next 12 months.”

Soil Engineering is currently on programme to complete the work on time despite the short days and difficult weather conditions, however the company has not seen the end of the site just yet. A provision exists within the contract to return in June 2013 for a three week period, to undertake any works requested by the main contractors during their tendering process.

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