Crossrail

Project brief: Suction Measurements and Small Strain Stiffness Measurements. Installation of wireless tilt beams and Shape Arrays.

GeO has made several hundred suction measurements and stiffness measurements on samples recovered from the route that will connect east and west London. Suction measurements can be used to estimate the insitu stresses and coupled with the small strain stiffness plays an essential role in the economic design of the tunnels in the very stiff London clay. GeO has also supplied tilt beams and Shape Arrays to monitor the displacement of buildings, diaphragm and piled walls.

Heathrow Terminal 2B

Project brief: Installation, reading, reporting and interpretation of instrumentation during the construction of a new basement structure. Permanent project team consisting of engineers, surveyors, geologists and technicians.

Instrumentation: Inclinometers, In-place inclinometers, Shape Arrays, GeO piezometers, Liquid Levelling System, Precise Levelling and Total Station Surveys,

A permanent team of six GeO employees installed over one hundred inclinometers into and behaind a diaphragm wall. Precise level and total staion surveys were also undertaken to monitor the stability of working terminal buildings during the construction of the basement structure. GeO engineers were involved in the daily interpretation of the data for reporting to the site construction and design teams.

Tottenham Court Road Station

Project brief: Installation of 32m Shape Array.

GeO installed a 32m SAA was installed inside a sonic hole within a concrete D pile and will be used to detect displacements when the Crossrail tunnels pass besides the pile in a few years time. Among the many advantages of the SAA system are that it can be installed inside a relatively small diameter hole without the need for grooved casing and it can be read directly onto a portable computer.

Wembley National Stadium

Project brief: Suction Measurements. Installation and reading of geotechnical instrumentation. Factual reports.

Instrumentation: Rod Extensometers, Magnet Extensometers, Inclinometers and vibrating wire piezometers.

GeO were involved from the beginning of this project, making on site suction measurements to assess the best compaction conditions to manage the highly expansive London Clay. To monitor the ground movements following the compaction GeO  installed 50m deep rod extensometers and 30m deep magnet extensometers, with VW piezometers being used to monitor the disipation of excess pore water pressures and inclinometers being used to monitor the deflection of bored piles used to retain the swelling clay.

Heathrow Terminal 5

Project brief: Suction Measurements. Installation and reading of geotechnical instrumentation.

Factual reports.

Instrumentation: 42 GeO piezometers.

This is another project where GeO was involved from an early stage. Suction measurements were again used to identify the best compaction conditions to manage the London Clay. Suction measurements were also used to estimate the in situ stress state in the London Clay. The tunnels for the extended Piccadilly and Heathrow Express Lines were constructed within 20m deep open excavations. Temporary stability of the steep sided London Clay slopes was continually assessed whilst the work was proceeding using GeO piezometers.

Northolt Park Railway Embankment

Project Brief: Planning, installation and reading of geotechnical Instrumentation.

Factual reports.

Instrumentation: 23 vertical inclinometers, 10 magnet extensometers, 30 GeO piezometers, 5 open standpipes.

This was a long term research site that was used to study the effects of progressively removing vegetation from an embankment. The instrumentation was installed between June and August 2006. The vegetation was progressively removed to study the effects of this on the behaviour of the embankment. GeO was the ideal partner for this work because of our expertise in installing instrumentation into slopes and our knowledge of the behaviour of embankments.

Wembley Light Maintenance Railway Depot

Project Brief: Installation and reading of geotechnical Instrumentation. Factual reports.

Instrumentation: 7 vertical inclinometers, 7 GeO piezometers.

This is a soil nailed cutting where doubts about stability have lead to the installation of inclinometers and GeO piezometers. The installation conditions were particularly difficult because the instruments had to be threaded between the nails that were no more than 0.5m apart. Depths of 14m were required with the top 8m containing soil nails at 1m elevations. A Terrier Dynamic Sampling Rig was used, first to dynamic probe each location in order to prove the ground and then to open up the boreholes to 100mm diameter in ordeer that 70mm diameter inclinometer casing could be used.

Magnolia Road Railway Embankment

Project Brief: Planning, installation and reading of geotechnical Instrumentation.

Factual and interpretive reports.

Instrumentation: 4 vertical inclinometers, 4 magnet extensometers, 14 GeO piezometers, 4 open standpipes.

This site formed part of a wide ranging study of the effects of climate and vegetation on rail embankments. The embankment is located at Southend-on-sea and is formed of compacted London Clay. It was densely vegetated and has a history of poor ride quality. The instrumentation was installed in March 2006 and monitoring continued to March 2010. Some vegetation was removed in the spring of 2007 and the effects of this were closely monitored.

Coal Pit Heath Railway Embankment

Project Brief: Planning, installation and reading of geotechnical Instrumentation.

Factual reports.

Instrumentation: 5 vertical inclinometers, 3 horizontal inclinometers, 23 GeO piezometers, precise track levelling.

This was a 15 month monitoring programme for a 20m high embankment on the Great Western Region near Bristol. The results of this monitoring identified the presence of soil suctions, which enhanced the stability of the slopes and enabled considerable savings to be made in the adopted design solution.

Northolt Railway Cutting

Project Brief: Planning, installation and reading of geotechnical Instrumentation.

Interpretive reports.

Instrumentation: 13 vertical inclinometers, 9 GeO piezometers,18 open standpipes.

This is a section of cutting on the Central Line between Greenford and Northolt. There is a history of slope movements at this location. A ground investigation undertaken by others in 1999 installed 5 inclinometers at the top of the slope and 14 mid-slope open standpipes. GeO assumed the monitoring of this instrumentation in November 2005 and installed additional instrumentation in February 2008 including mid-slope inclinometers and GeO piezometers.

Highway Projects:

M25 Motorway Escarpment at Godstone

Project brief: Planning, installation and reading of geotechnical instrumentation.

Interpretive reports.

Instrumentation: 42 vertical inclinometers, 48 GeO piezometers, 9 open standpipes, 8 siphon wells with water level recorders,1 in-place inclinometer.

This is a natural slope with a series of pre-existing landslide adjacent to the M25 motorway. GeO has been monitoring the escarpment since November 2002. Originally we took over the post construction monitoring for the remedial works following a major landslip (Flint Hall Farm) that occurred in December 2000. Since March 2003 we have also been monitoring the movement of another section of the hillside (Rook’s Nest Farm).

M11 Motorway Cutting at Chigwell

Project brief: Planning, installation and reading of geotechnical instrumentation.

Interpretive reports.

Instrumentation: 13 GeO piezometers

This is a remediated slope where a landslip had occurred. The remedial scheme involved drainage and regrading of the slope. GeO piezometers were installed in 2005 before the remedial works to assist in designing the drainage and more piezometers were installed after the remedial works were completed to monitor the effectiveness of the drains and hence the remedial works.

M1 Motorway Embankment at Edgewarebury

Project brief: Planning, installation and reading of geotechnical instrumentation.

Interpretive reports.

Instrumentation: 17 vertical inclinometers, 15 GeO piezometers and 1 open standpipe.

This is a London Clay embankment with superficial evidence of numerous slips. The instrumentation was installed in July 2007 and is being used to identify the depth of these slips and to assist in identifying the need for any remedial works.

M25 Motorway Embankment at Potters Bar

Project brief: Planning, installation and reading of geotechnical instrumentation.

Factual reports.

Instrumentation: 17 vertical inclinometers, 15 GeO piezometers.

This is a London Clay embankment where significant slippage has occurred. GeO installed the instrumentation here which included four 20m deep inclinometers installed through the hard shoulder during night time works.

A1(M) Cutting at South Mimms

Project brief: Planning, installation and reading of geotechnical instrumentation.

Factual and interpretive reports.

Instrumentation: 9 vertical inclinometers, 9 Magnet Extensometers, 28 GeO piezometers, 1 open standpipe.

This is a cut slope where superficial slips have occurred. This study involves repairing the slope using polypropylene fibres in an attempt to reduce the amount of shrinkage and swelling that can occur after the slope has been repaired. The instrumentation is being used to measure the ground movements and pore water pressure changes that occur.