Ground Investigation Projects
Grouting Projects
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A3 Hindhead Improvement Scheme
Client: Highways Agency
Consulting Engineer: Mott MacDonald
Contract Value: £600,000
Soil Engineering carried out the Phase 1B ground investigation for the A3 Hindhead improvement scheme. The ground investigation work was to enable the detailed design of the earthworks, deep cutting, structures and revised tunnel alignment for the proposed 5.7km route.
The ground investigation comprised cable tool and rotary boreholes, shallow and deep machine excavated unsupported and supported trial pits, soil and rock sampling as well as specialised in situ testing.
Cable tool boreholes were formed throughout the route investigated to depths of up to 30m, a number of which were selectively extended by rotary coring techniques. Rotary open and cored holes were also formed to between 40m and 75m depth. A total of some 400m of 100mm diameter cores were produced by triple tube drilling with a predominantly foam flush. The foam was required to be carefully controlled and suppressed in several cases when expelled at the surface because of Landowners' concerns.
Several of the exploratory hole positions were within environmentally sensitive areas (SSSI / SPA) which required Soil Engineering to take the appropriate planning of preventative measures and subsequent supervision to prevent any contamination and unavoidable disturbances.
One of the rotary boreholes that were formed, was drilled to 95m at an inclination of 45º utilising the Geobore "S" wireline system. The hole was drilled with an inclination tolerance requirement of 1:100 through weak, unstable and fractured sandstone with an average core recovery in excess of 95%. This allowed full geological descriptions and very detailed fracture logging and orientating to be undertaken. On completion the hole's overall orientations were checked to be within 1º in both inclination and direction.
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