Projects

Research

Southampton University

Lankelma has recently teamed up with Southampton University to help with an ongoing research project. The project was to investigate old pylon foundations. The research is partly founded by the National Grid and its maintenance contractors.

The purpose of the investigation was to delineate the shape of the foundations and secondly to gain geotechnical properties of the back fill material. After discussions with Southampton university’s geotechnical research department and an initial trial, we came up with a system which best suited this particular job.

Lankelma used its versatile CPT frame, which has been used for a variety of job types in the past. The frame was used so as to be able to get as close to the foundation as possible. The rams on the frame can be mounted either over the end of the frame or in centre.
The reaction force was provided by concrete blocks mounted on either end of the frame. The frame and the box were moved around the site using a Hiab truck. One big advantage of the frame in this situation was that the rams could be moved laterally to a different position without moving the frame itself.

CPT’s were carried out on the foundations of two pylons. The tests were spaced out with a distance of as little as 20cm between them so as to accurately gain a profile of the foundation. The CPT was pushed into the ground until it hit the foundation and refused. We also took some MOSTAP samples at the site for laboratory testing.

The testing proved to be successful with good results being obtained. This work has proved that CPT’s are an innovative method of ground investigation with applications in many different environments. This is also another example of Lankelma’s commitment to research and advance in the use of CPT’s.

Special Guests

Lankelma CPT Ltd was very honoured to have two well respected guests visiting their Iden Offices. Two of the authors of the book Cone Penetration Testing in Geotechnical Practice, Tom Lunne form NGI in Norway and John Powell of BRE in the UK came over to discuss developments in cone testing.

On the photo you can see Lunne and Powell with technical director Andy Barwise and geotechnical engineer Darren Ward in Lankelma's cone workshop

New pressure meter at Lankelma

Lankelma CPT Limited has recently completed two projects successfully using a new driven pressuremeter (DPM) developed by its sister Company Setech, who are based in Newcastle.
This new instrument has undergone extensive, and successful, trials at the BRE Cowden Test bed site on the East Yorkshire coast.

The new (DPM) has a membrane length to diameter ratio of 8 and which ensures that the instrument has a predominantly radial expansion of the pressuremeter membrane during inflation.

The (DPM) is attached to the CPT push rods and the instrument is advanced into the ground using the CPT hydraulic rams. At the desired test depth the penetration is paused and the expandable membrane is inflated using compressed gas. The tests are performed in a stress and strain controlled manner using a strain control unit (SCU). The SCU controls the pressure rate during the initial part of the test such that an adequate number of data points can be collected to adequately define the initial loading curve from the initial part of the test. Once plastic yield of the soil around the DPM occurs, the SCU limits the expansion rate to a predetermined value.

Once the membrane has lifted off the instrument body and membrane expansion commences, unload - re-load loops are typically performed. The magnitude of these loops are controlled to prevent failure around the cavity and to enable the determination of the soil elastic properties.

In addition, the (DPM) membrane can be inflated to a large radial strain of approximately 50 per cent, to ensure that the pressuremeter Limit Pressure is approached at full inflation.

The new (DPM) has proven to be successful both on land and off-shore, and when used in conjunction with CPT technologies provides an economical and technical alternative to the Self boring pressuremeter as well as the pre-drilled Menard pressuremeter.

LANKELMA RESEARCH

T-Bar Cone for Soft Soils: Lankelma research with University College Dublin and Norwegian Geotechnical Institute

Lankelma CPT Limited has recently completed a programme of field works in Ireland with Dr. Mike Long at the Department of Civil Engineering, University College Dublin (UCD), to assess the performance of a novel cone penetrometer to measure the undrained shear strength of soft soils. Three ‘high’ plasticity soft clay sites were selected for investigation. This data will augment the data of the NGI sites and has predominantly been obtained from sites comprising soils of ‘low’ plasticity.

The T- Bar consists of a short cylindrical bar measuring 250mm in length and 40mm in diameter that replaces the conventional 60 degree cone and is attached at right angles to the penetrometer rods just below the calibrated load cell. Also included in the shaft is an inclinometer to indicate any deviation from the vertical during penetration. The device can also have incorporated pore water pressure transducers. The T- Bar cone has two major advantages over the conventional electric cone. Firstly, the load cell measures what is essentially a differential force (or net pressure)on the bar, so that no corrections need be made for the overburden stress and ambient pressure.

Secondly, the correlation between net pressure on the bar and the shear strength of the soil is by an exact plasticity solution, with a potential range of bar factor of less than 10% (due to different roughness of the bar surface), compared with cone factors that range from as low as 7 for sensitive soils to over 15, that is a range of 35%.

An additional use of the T-Bar is to assess the remoulded strength of the soil, by monitoring the bearing resistance during extraction along the same path as insertion.

Hopefully, the combined UCD and NGI data will provide a reliable correlation between the undrained shear strength and T-Bar penetration resistance for soft soils that range from low to high plasticity. The results of this work are to be published in the near future. For further information contact Brian Georgious at our Regional Office 01244 289 356.

Regents Park

‘Lankelma CPT Limited has recently been requested by Geodelft, as part of the CONVURT Consortium

Lankelma CPT Limited has recently been requested by Geodelft, as part of the CONVURT Consortium, to investigate the vibration radiation from underground railways and the possibilities of reducing these vibrations to perform dual seismic CPT tests in Regents Park, London. The seismic cone is a specialist tool, which incorporates a dual seismic cone with the triple element geophone separated by either a 1.0m or 0.5m.

green field sites brown field sites motorways railways waterways and flood defences marine

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