Projects

Testing in Limited Spaces

Deep Deep Down

Recently, Lankelma CPT Ltd has again demonstrated its ingenuity and versatility of the CPT by carrying out a very ambitious development program. The work was carried out 154 steps down (about 30m with no lift!) beneath London, in an underground tunnel.

The work was carried out in partnership with one of the Underground operators as part of their tunnel assessment program. Although carrying out CPT’s in basements of buildings beneath road level is something that Lankelma is very experienced in, this particular job had a small twist!

That twist was that the CPT’s were not required to be taken vertically down as usual but at a nearly horizontal incline through the sidewall of an underground tunnel. This was an interesting challenge; but nevertheless one that Lankelma raised to- drawing up many different novel and exciting ideas.

The chosen solution was the most simple which involved attaching Lankelma’s special ‘Basement’ set of CPT rams to the tunnel wall lining. Simple. But not easy. Many different constraints were put on the testing due to the special environment that it was working in.

Firstly, a core in the tunnel wall needed to be drilled to allow for the cone to penetrate. Once it was drilled, the rams were attached to the tunnel wall in line with the hole.

As part of the development program, different types of testing and sampling were carried to in order to assess how they behave in such an environment so as to work out the best-suited techniques.

Firstly, two different sampling techniques were carried out, the first being MOSTAP soil sampling. This is the standard system used on land with ‘normal’ CPT rigs. It gives you 65mm diameter by 1m long samples. Two meters were taken with this system.

Secondly, a thin wall Shelby sampler was pushed in. This technique is commonly used on offshore CPT systems. Again, two samples were taken at the same location giving sample of 65 mm and 1m in length.

After a successful 100% recovery from all four of the samples, the rig was moved to a new position to carry out the testing. Again two different methods were used, the first being the seismic piezocone. This was set up with two seismic modules each with three geophones inside; two to measure ‘S’ waves and one to measure ‘P’ waves. In front of these modules was a piezocone measuring the excess porewater pressure in the shoulder (U2) position.

This was pushed into a depth of 5m taking seismic measurements every half a meter. The seismic results were not so good, but this was expected due to the nature the of the source. The PCPT results were very good, showing the expected results.

The second type of testing that was carried out was a push-in Pressuremeter. This was again pushed in using the CPT rams, which had been moved to a new position. Three tests were carried out down the same hole. This gave excellent results allowing us to gain small strain stiffness and many other parameters.

This example shows how versatile CPT’s are, how they can be adapted to any location and any situation. It also shows that by working together with the client at an early stage, cost effective solutions can be arrived at whilst at the same time pushing back the boundaries of innovation.

Dr. Wouter Broere has written a dissertation on horizontal cpt. Click here to read his article.

Click here to view a short movie showing horizontal CPT in action.

Push in instrumentation under an angle

One of the advantage of cpt rams are their versatility. We can make cpt's under any angle. Another use you can see on the accompanying photos is pushing in instrumentation under an angle. This makes otherwise awkward jobs relatively easy and mess free. We have carried out projects under buildings, railways, canals. Un unusual use was to survey the depth of the foundation of an old church by probing in a number of angles. In this case a detached set of rams is used using the hydraulics and counterweight of a truck. The detached set of rams can be used in all sorts of environments like cellars, tunnels and any place with limited access or headroom.

Versatile CPT

Lankelma is showing how versatile you can be with a set of cpt rams. The rams on the cantilever frame can make vertical cpt's as well as cpt's in an angle. Cpt's were made along he bottom of the embankment.

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.

Flying High.....Pushing Deep

What do you do if you have a job beneath a rail bridge, with no access in or out; full of piles that can’t be touched and you need some ground investigation? You call Lankelma and their Minicrawler CPT rig!

Recently, Lankelma was approached to come up with a method of testing the ground beneath a railway bridge on the CTRL. The ground had been capped with concrete and grout pipes were sticking out of the surface which couldn’t be damaged. The underlying soils needed to be tested before it was treated with ground improvement methods, and then tested afterwards to verify that the ground improvement had worked.

Because of the access problems posed by the sites location, Lankelma sent its 3.5 tonne Minicrawler along to do the job. It was craned down onto the site using an onsite crawler crane. Once the rig had landed, it had to move carefully through the maze of pipes that covered the floor. Due to the rig only weighing 3,5 tonnes, extra reaction force was gained by bolting the rig down to the concrete floor.

The Mincrawler was able to carry out 5 tests over the two day period down to a depth of 5 to 10 metres.

The Minicrawler is a versatile CPT rig. Due to its size, it is able to work on sites where a standard CPT rig would not be able to gain access. With its multi-angle rams, it is designed for slope and embankment work. The reaction force of the rig can be increased by screw picks in the soil, bolting it down to concrete, or by adding kentledge weights.

Going Underground

Lankelma has just completed a basement job showing that CPT’s can be carried out almost anywhere.

The job was carried out in the basement of an important building in central London. The basement had been extended beneath the road that passed outside the building. This extension had recently started to subside and cracks had formed in the walls and floor. A ground investigation was needed as a step to prevent any further subsidence.

There was a height restriction of less than 2.2m, with pipes and air-conditioning shafts that reduced the working height in even more places. Access to the basement was by foot only down a series of stairs.

Due to the restricted access, a drilling rig and a conventional CPT rig was ruled out. Lankelma’s basement rig was the best choice for the job. It can work in areas with only 1 metre of headroom. It is hand portable, so can therefore be carried to locations. It can get its reaction from either bolting down to a concrete floor, adding kentledge or pushing from the roof.

For this project, the rig was bolted to the floor. The CPT reached a depth of 18.3m penetrating through the Terrace Gravels and into the London Clay. The requirement was for only one CPT, but generally, for basement work, 2 to 3 tests can be carried out in a day. This was just another example of how versatile CPT’s are.

CPT inside a Warehouse?

Recently Lankelma undertook a more difficult CPT job inside a warehouse. The job was inside a working warehouse with restricted access and sensitive working conditions. The investigation was to find the underlying soil condition for the possible building of a new housing development.

Originally Boreholes were going to be used to do the entire job. Some were done in the outside loading area of the warehouse.Considering the time they took to do and the noise and mess they caused, it was deemed unsuitable for this method to be carried out inside the working warehouse. Disruption of the day to day running of the warehouse also needed to be kept to a minimum.

CPT’s were then proposed to carrying out the required testing inside the building. Conditions were very tight inside the building but with some skilful driving the truck made it inside. Exhaust fumes had to be extracted using a fan and piping.

Three tests were carried out down to refusal. Final depths were around 20 metres. At each location the concrete floor was cored before the CPT was carried out. The testing took just over 3 hours. CPT’s allowed for all the testing to be carried out in one day and with the minimum of mess. Results were produced for the next working day.

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

research testing in limited spaces restricted access