This category celebrates innovative, unusual or cutting-edge approaches to environmental and sustainability issues on a geotechnical project, between January 2021 and March 2022.

Bachy Soletanche and Vibro Menard: Eco Park South, North London Heat and Power Project

Bachy Soletanche and Vibro Menard delivered the geotechnical works for the first phase of Eco Park South. The team developed an environmentally friendly solution which contributed to an overall reduction of between 10-16% of the total embodied carbon in the ground engineering element of the works.

The key drivers were the usage of controlled modulus columns, which enabled the client to use a thinner slab with less reinforcement, and the use of the Trenchmix method to construct a cut-off wall instead of using a traditional sheet piled solution. Adopting these two processes also reduced the number of vehicles used for spoil removal and the number of deliveries to site for cages and sheet pile panels.

Bachy Soletanche, Balfour Beatty Ground Engineering JV and PJ Davidson: Slip formed guide walls for diaphragm and secant walls

SB3 is a joint venture of Bachy Soletanche and Balfour Beatty Ground Engineering. Working with Balfour Beatty Vinci JV, SB3 and PJ Davidson used slip-form guide walls on High Speed 2 (HS2) sites to reduce carbon emissions.

Currently all guide walls for ground engineering purposes are constructed using traditional in-situ methods. Using slip-form guide walls allowed the team to follow a shape optimised for structural efficiency, which is more efficient in transferring loads per tonne of concrete and steel used. What’s more, attaching the slip-form to a paver does not require any formworks for the diaphragm guide wall.

This innovative method has saved at least 830m3 of concrete over 2.5km of guide wall on HS2’s Burton Green Tunnel structure alone. The team were able to build 80-100m of guide walls per day, making the works up to eight times faster than conventional in-situ methods.

Balfour Beatty Vinci and Mott MacDonald Systra: Numerical 3D ground modelling to support material reuse assessments

The integrated project team working on the HS2 phase 1 area north has used a new digital engineering technique to help optimise the mass haul strategy across the section.

This technique was developed through a collaboration between Balfour Beatty Vinci and the design joint venture Mott MacDonald Systra. It combines 3D ground modelling and numerical analysis. It has enabled the project team to achieve mass haul efficiencies and associated carbon reductions while also reducing residual risks during construction, particularly the need to import additional fill to site.

The scale and nature of HS2’s lots N1 and N2 has warranted this hi-tech advancement. However, the technique can be readily applied to any infrastructure project that involves mass movement of material. It is particularly useful for obtaining a more accurate picture of the volume and location of key material classes within an excavation. This allows teams to better plan their mass haul strategy.

Bam Ritchies: Rock and roll stars

Drill and blast contractor Bam Ritchies supports the production of more than 40% of the UK’s aggregates. It attributes its success to working collaboratively with clients and discussing their requirements and what optimisation it can deliver for them to reduce their carbon footprint.

Over the past three years, Bam Ritchies has invested in new equipment to ensure it has the most sustainable, fuel efficient and productive plant available to its clients. It uses electronic delay detonators during excavation, which saves its customers fuel, reduces electricity usage and brings down drill and blast costs. Pyrotechnic blasting techniques can eliminate the need for carbon heavy mechanical breakers and deliver dimensional, low vibration rock breaking operations.

Costain, Vinci Grands Projets and Bachy Soletanche JV (CVBJV): Tideway East – Remediation and ground improvement of Earl Pumping Station

A complex ground improvement scheme has been designed and installed by CVBJV at Earl Pumping Station (EARPS), one of the Thames Tideway East sites. This is to enable the excavation and permanent works for the combined sewage overflow chamber to be carried out.

EARPS is highly contaminated because of its history as a tar works. As a result, the soils and the upper aquifer are contaminated in the area where the geotechnical works took place.

CVBJV has overcome these issues through its ground improvement processes. This involved injecting a grout mix into the Thanet Sand Formation and the river terrace deposit to bind the soils in the area and prevent any drawdown of contamination.

CVBJV opted for low carbon cement replacements – a combination of ground granulated blast furnace slag and a standard concrete mix – as a replacement for the grout cement binder for the deep soil mixing and jet grouting.

A planning condition for a West Midlands housing scheme required an 80,000m3, 9.5m high, 450m long visual and acoustic bund to screen new homes from an adjacent industrial site.

Fundamentally important was the bund’s sustainability and commercial viability. This was achieved by constructing it entirely from fill contaminated with hydrocarbons and heavy metals. This would otherwise have gone into landfill, but it was imported under licence, treated on site and then reused in the bund.

Geosynthetics was approached by ground remediation specialist Dunton Environmental to evaluate possible solutions. To achieve the required steep 70-degree face towards the industrial site Geosynthetics designed a “wrap around” geogrid reinforced slope.

Analysis of particle size distribution and shear box tests of the embankment fill enabled the solution to be optimised – selecting appropriate grades, lengths and vertical spacing of the geogrids.

Construction of the bund was completed in September 2021.

Keltbray: Design and installation of Hiper piles for structural and geothermal capacity

Hiper pile stands for a hollow, impression enhanced, precast, energy generating and re-useable pile system. It is a completely new approach to bored piling.

The Mace Dragados office and welfare facility at HS2 Euston Station is the first site benefitting from the full Hiper offering, implemented as part of HS2’s innovation programme. Forty Hiper piles were installed with impressions along the shaft to increase capacity. The internal void was thereafter filled with water allowing the piles to act additionally as heat exchangers – these are 60% more thermally conductive than solid piles.

In-situ and precast versions were deployed, demonstrating programme advantages and zero waste for follow-on trades. Over 280m3 concrete was saved and additional carbon savings will be obtained from the ground source heat pump system and pile reuse in the long term. The data emerging presents a case to use Hiper piles on the wider HS2 development.

Mott MacDonald: Rehabilitation of Gumbasa irrigation system following Palu earthquake

In 2018, a powerful earthquake caused extensive damage to the 55km Gumbasa primary canal in Central Sulawesi, Indonesia, which irrigates more than 60,000ha of land.

Mott MacDonald developed a concept and design for the reconstruction of the primary canal. It undertook engineering and sustainability assessments. Challenges arose from rare earthquake induced, high velocity flow slides, for which only basic types of investigation technology were available for ground characterisation.

Its solution was to install a geogrid reinforcement with precast segmental canal linings to accommodate large seismic accelerations and permit rapid repair in the event of exceeding performance limits. Downslope counterfort drains were adopted to relieve excess pore water pressures during future earthquakes.

Mott’s engineering assessment, repair and rehabilitation of the main canal considered the environmental, social and economic sustainability considerations of the region and its people.

Sanctus: The Forge Dam restoration project, Porter Brook Valley, Sheffield

Forge Dam is one of the few remains of Sheffield’s industrial heritage. The project to restore the dam saw Sanctus overcome various obstacles. Forge Dam is in a narrow valley with extremely constrained access. As a result, the team had to work collaboratively and imaginatively to find a way to allow continued public access through the site. At the same time, it needed to ensure operations could be carried out safely in extreme weather conditions to protect the public, wider river environment, the local road network and the confined species-rich wet woodland.

The project to restore the dam provided economic and environmental benefits to the local community. The restoration also ensured that an established wide range of biodiversity was retained. This provided opportunities to reintroduce species, create new habitats for wildlife and raise environmental awareness within the community.

Vertase Fli: Lostock energy from waste power plant

Vertase Fli carried out remediation and earthworks for a proposed energy from waste (EfW) power plant at a site in Lostock near Northwich that used to be host to a soda-ash production facility. Soda-ash production produces substantial volumes of waste lime (galligu) as a by-product. It is estimated that 100,000t of galligu was deposited on the site and local area annually. Galligu has high moisture content and zero shear strength. As such, it is geotechnically unsuitable. Typically, galligu is either disposed to landfill or is prohibitive to redevelopment.

Vertase Fli carried out research and bench scale trials to demonstrate the strength and long-term durability of the selected stabilisation method and successfully applied the treatment in the field. Successful remediation and site reuse of galligu waste is substantially cheaper and more sustainable than disposal. Successful application of the method implemented by Vertase Fli could potentially unlock a significant amount of brownfield land for redevelopment.

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