The Remedy for unstable slopes

Remedy Geotechnics provides its clients with ready access to experienced, independent geotechnical design. Derek Egan, the company’s founder, explains how Remedy Geotechnics uses up-to-date design methods, including advanced finite element modelling methods, to stabilise slopes.
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Remedy Geotechnics is able to undertake slope stabilisation projects where access is limited

Derek Egan

Through many years of experience working for contractors, civil engineering designers and client organisations, Remedy Geotechnics knows how to balance innovation and practicality within a project's timescale.

With a wealth of knowledge on the use of many slope stabilisation approaches, including the use of products such as ground anchors, reticulated piles and soil nailing, Remedy always seeks to provide the optimum solution to the prevailing site situation. Remedy also has particular expertise in the design of soil nail facing systems.

Slope stabilisation requirements usually fall into one of two situations. Firstly there is the stabilisation of new cut slopes, for example the 420m long and 9.8m high retention required in Exeter, UK, to enable a new IKEA store development and secondly the stabilisation of existing slopes that have failed, such as the 30m high slope failure that occurred adjacent to the B4286 in Cwmafon, South Wales.

Exeter soil nailing

The brief Remedy Geotechnics was given was to provide support to a steep 9.8m high, 70-degree excavation, which also had to support a highway and associated structures to enable the development of a large retail unit for Swedish furniture retailer IKEA.

Remedy's solution was to design soil nailing to use a self-drilling bar and grout flush drilling system and a facing comprising a structural rear mesh with stone filled panel cladding. This sort of finish can provide a more aesthetically pleasing appearance than, for example, shotcrete or plain concrete.

 emedy eotechnics soil nail structure provides support to the 379 road and provides an aesthetically pleasing appearance Remedy Geotechnics soil nail structure provides support to the A379 road and provides an aesthetically pleasing appearance

 

Remedy carried out the design of the 420m long excavation face for specialist geotechnical contractor Aarsleff Ground Engineering. The soil nail structure has a design life of 100 years and provides support to the A379 road to the northern boundary of the site, Newcourt Way to the west and the access road to the retail development to the south.

In this type of application, soil nailing has the benefit of a top-down construction sequence, therefore, providing support throughout the excavation sequence in both the temporary and permanent situation. This makes the technique time efficient to implement. The ground conditions comprised a competent sand layer near surface becoming a very weak sandstone with depth.

The design was carried out in accordance with BS8006-2 (2011) employing the latest design techniques and in-house, industry-leading, expertise. Sacrificial soil nail testing, in accordance with BS EN 14490:2010, was carried out prior to the main works and showed full agreement with the selected design parameters. In total 1,090 soil nails were installed. Each excavation stage was carefully considered in the design to ensure temporary stability during the construction process. In this type of situation, the structural rear mesh backed with a filter geotextile can be used to enhance short-term face stability, and is then, of course, in place to use in the permanent condition as well. Once the whole excavation was complete with this temporary support, the rear mesh was then clad with stone-filled panels to provide a low-maintenance aesthetic facing.

Cwmafon landslip

When a landslip affected a 30m high slope above the B4286 road at Cwmafon, South Wales, Remedy Geotechnics worked with contractor Quantum Geotechnical and Neath Port Talbot Council to stabilise the slope.

The landslip had prompted a partial road closure and Neath Port Talbot Council needed the road reopened as quickly as possible. By working with key stakeholders, in particular, the local authority, Remedy was able to get fast track approval for ground investigation and preliminary nail testing. Detailed design and Category 2 checking quickly followed.

 ractical limitations had to be taken into account when decided the best techniques to stabilise the slope at above the 4286 road in ales Practical limitations had to be taken into account when decided the best techniques to stabilise the slope at above the B4286 road in Wales

 

The main cause of the problem was the instability of around a 2m thickness of superficial weathered soil and rock losing adhesion with the underlying Brithdir Member sandstone. From historical information studied, it appears the cutting side slope has been in existence since at least the mid-19th century and may, in fact, have formed a relic river valley side slope surviving from the last ice age.

The slope's significant height and situation required Remedy to consider the practical limitations of what could be installed to stabilise the slope first, before moving onto the detailed design work required to demonstrate the measures were robust. This is where the practical experience of the Remedy team could be most efficiently brought to bear on the problem. After some consideration, it was decided that the upper nails and facing mesh could be installed using roped access techniques while on the lower parts of the slope a long-reach excavator attachment could be used within the narrow road land closure space.

Paying close attention to keeping costs down while maximising efficiency, Remedy found that adopting a high-strength Geobrugg Tecco G65/3 steel mesh facing secured to the underlying sandstone bedrock with a self-drilling soil nail kept manual handling to within manageable limits while providing a robust solution. Particular care was taken to ensure the mesh was tensioned down onto the slope face, improving the resilience of the overall stabilisation measures.

Summary

Backed up by experience from our professionally qualified geotechnical engineers, Remedy employs the latest design techniques fully integrated with the latest design codes and best practice guidance. Whether it is an efficient preliminary or tender design or a full design for construction, Remedy will always seek to supply a comprehensive, effective and economical solution for any slope retention project.

Our practical construction experience can also be brought to bear to investigate and diagnose sites to formulate an effective geotechnical strategy to maximise opportunity and minimise risk.


After many years of working for large geotechnical engineering companies, Derek Egan started Remedy Geotechnics, a company that reflects the high standard of design that he believes to be consistently achievable - and non-negotiable

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