Sergio Solera, the BGA committee member responsible for organising the competition and finals event, writes that Dr Christine Cooling, daughter of Dr Leonard Cooling after whom the award is named, opened the proceedings by explaining the pioneering work on soil mechanics that her father carried out at the Building Research Station from the 1930s onwards and how he promoted the idea of creating a prize for young practitioners of geotechnics.
The presentation by Francesc Mirada (Arup) was on the Material Point Method (MPM) in slope stability analysis. He used data from the Selborne Cutting experiment (9m cut in Gault Clay induced to fail by pore water pressure increase) to validate and expand the work done by others using the MPM so that its results can be used to explain better the conditions leading to failure of the slope and to follow the time of the post failure behaviour of the unstable mass of soil.
Vipul Kumar (Mott MacDonald) presented his paper on Development of 3D numerical models for optimisation of ground improvement for bored tunnels in marine clay. Vipul explained how at-grade roads built over the notorious soft marine clays will be affected by ground loss due to climate change induced by sea level rise, thus requiring additional fill.
Vipul used Plaxis 3D using advance constitutive models such as Soft Soil to model the soil-structure interaction between the tunnel lining and the consolidating soils. As the permitted road tolerances are very tight (15mm and 1:1000 over 3m of tunnel) jet grouting is proposed and modelled in Plaxis at the transition of the tunnels into the stations, based on previous experience and the use of EC7 to evaluate the raw GI data.
Ronan Royston (Oxford and Ward and Burke Construction) gave a very interesting presentation on the Monitoring of the construction of a large diameter caisson in clay. The data presented is quite unique, being constructed using 1m thick in situ reinforced concrete sections, sunk in soft clays.
An innovative levelling system to within 1mm was used, together with Cambridge type Stroud load cells to measure normal and shear stresses, installed at the leading cutting edge and 5.4m above, to monitor the stresses sinking. Real-time data was provided to the site engineer to control the shaft sinking and will also provide data for future design of this type of shafts. The presentation included a video of the caisson sinking during construction and sinking.
Daniel Martinez Calonge (Imperial College) presented a paper on Investigating the thermal conductivity of London Clay. Work done in the laboratory on intact and reconstituted samples highlighted the effect of permeability, mineralogy, anisotropy, strength, and density in the evaluation of the thermal conductivity of soils.
The presentation showed that certain published data on thermal conductivity in London Clay could not be replicated in the laboratory. As thermal conductivity is a key parameter in the design of geo thermal structures (energy piles, thermos-active tunnels etc.), getting this parameter wrong may lead to the failure of the thermal equipment of the structure.
While the judges considered the presentations, Prof David Toll of Durham University delivered an excellent presentation on Suction in unsaturated soils. Prof Toll explained that the new tensiometer developed at Durham University is capable of measuring suction up to 2MPa; previously only readings up to 100kPa were possible due to cavitation.
Field data from an instrumented embankment constructed with glacial till of medium plasticity (Durham Till) near Newcastle shows that the drying and wetting process leads to the long term degradation of the soil, with the undrained shear strength reducing with time for a given moisture content. Prof Toll suggested that measuring suction may be a better indicator than the moisture content. This degradation should be expected in the upper shallow soils, extending less to 1-2m depth.
All the presentations were of a high standard but after much deliberation the judges awarded the 48th Cooling Prize Competition to Francesc Mirada of Arup. He was presented with a crystal decanter, £200 from Ground Engineering, a Rudolph Glossop book, and various opportunities to develop his career, not least to deliver his paper to the BGA Annual Conference on 21st June 2017 and represent the BGA at the International Young Geotechnical Engineers Conference in Seoul in September this year.