Working on an Island

Constructive Evaluation was commissioned back in February to carry out a Site Investigation to an island situated on the River Thames. The purpose of this investigation was to provide detailed lithology and soil strength parameters for the substrata at two locations around the Island. From this, we could determine whether the ground was suitable to redevelop a disabled access fishing platform in one location and construct a new fishing platform in another location.

Before we could carry out our investigations, we first had to get to the island. The footbridges used by pedestrians weren’t wide enough for our vans. Weight limitations on the bridges also ruled out the possibility of manoeuvring our equipment on foot. Fortunately, the river Thames happens to be a convenient waterway. Therefore, we hired a Knuckle Boom Crane mounted to a pontoon, loaded on our Archway dart rig and set off on a journey down the Thames to the site. Watch the video below to see a time lapse snippet of the journey.

Upon arrival to the site, we carried out the following tests to examine the soil’s suitability:
• Two windowless sampler boreholes to a maximum depth of 5.45mbgl
• Standard Penetration Testing at 1 metre intervals within the windowless sampler boreholes to
5.0mbgl. This form of testing is completed using a 63.5kg drop hammer weight, over a 750mm drop, measuring the blow counts for six, 75mm increments. The first two values are recorded as seating blows, with the remaining four values, added together to provide an ‘N-value’.
• Two dynamic probe tests to 15.0mbgl/refusal. This form of testing is completed using a 64kg drop hammer weight, over a 750mm drop, measuring the blow counts for the penetration of 100mm increments
• Hand shear vane tests within the borehole inspection pits. This test involves inserting a vaned rod into the ground and rotating. A measure on the top of the rod indicates the torque needed to cause failure of the soil.
• Geotechnical and Environmental laboratory testing. Tests included moisture content, particle size distribution & plasticity. Click here for more information on our lab testing

The client now has all the information we collated. Design calculations are currently underway for the new fishing platforms.

If would like more information on the other geotechnical testing services we offer, please click here. For a competitive quote or to discuss our services with one of our qualified surveyors or engineers, contact us here