Hothfield Site Investigation

Details

Concept Engineering Consultants were commissioned to undertake a geotechnical site investigation to understand the ground and groundwater conditions of a railway embankment. The purpose of the site investigation was to provide parameters for geotechnical design of a proposed retaining wall or regrading of the embankment slope.

The scope of the investigation comprised:

• 2 No. Dynamic Sampler Boreholes to a maximum depth of 10.70m;
• 2 No. Hand Held Dynamic Sampling Boreholes to a depth of 3.00m;
• Logging and Photographing;
• Geotechnical & Chemical Testing.

Challenges 

The site comprised a section of sloped railway embankment adjacent to Network Rails railway track, associated infrastructure and sloped embankment. Ground cover comprised track ballast and thick vegetation.

Access to the site was via a Road Rail Access Point (RRAP) on nearby Water Lane where all of the necessary investigation equipment was loaded onto trolleys and pushed some 1.2km to the point of work.

All works were undertaken in 2No. consecutive 12-hour shifts within a continuous 27-hour Network Rail Possession of the section of line which commenced 1.55am on Sunday 1st July 2018 ending at 4.45am, Monday 2nd July 2018.

Shift 1 team comprised operatives, Concept staff, roped access specialists and track trolley operatives. This team was charged with getting all plant and equipment to site, preparing the ground and access downslope and commencing the intrusive works at both the top and toe of the embankment. Shift 1 Team received their site induction and briefing at 1am 01/07/18 prior to commencing work on track

Shift 2 team comprised operatives, to Concept staff, Roped Access specialists and Track Trolley operatives. This team was charged with completing all the intrusive works, reinstatement and demobilising all plant and equipment from the point of work back to the Water Lane Access. Shift 2 team received their site induction and hand over briefing at 1pm on 01/07/18 prior to commencing works on track.

For works at the top of the embankment and nearest the railway track were undertaken using a Premier 100 Modular Rig modular window sample Rig. This was dis-assembled for transportation and moved using a track trolley from the site access at Watery Lane to the point of works at the embankment.  The rig was assembled on position by Concepts drilling crew.

Works at the toe of the embankment furthest away from the line was undertaken using a Hand-Held Window Sampler. Again, this was transported to the point of work using the track trolley and lowered into position using the specialist Roped Access team, following a period of vegetation clearance and preparation.

All drilling Crews held NVQ Level II in Land Drilling, PTS trained and audited annually by the BDA. For safety, all operatives and team members working on the embankment were tethered with fall arrest systems and lanyards supplied and fitted by the specialist Rope Access Team.

Outcome

All of the field works were completed safely within the 27 hour Possession and each 12 hour shift of Team 1 and 2 and to the satisfaction of Network Rail and Balfour Beatty.

The deliverables of the field works were successfully achieved despite the challenges of the working environment; semi-rigid plastic core liners were recovered from each borehole location.  The excavated soil was logged and photographed and representative, bulk and disturbed samples were taken for soil analysis. Environmental samples were taken for chemical analysis from all exploratory holes. Headspace readings for volatile organic compound (VOC) content were taken using a Phocheck Tiger photoionization detector.

The samples were delivered to our geotechnical laboratory and the specialist chemical analysis testing laboratory within the specified time frames. The geotechnical profile of the embankment was accurately identified and the parameters there of established through a suite of geotechnical laboratory testing.

A factual and interpretative report was produced for the Hothfield site investigation, all of which was delivered on time, on budget and to the complete satisfaction of Balfour Beatty.