Geo-polymer resin and subsoil injection for soil stabilisation

Concrete, Feb 2004 by Brierley, Marcus

Geo-polymers, supplied by Uretek UK, have been used to consolidate foundation soils for the last decade. This has become an important and accepted technique used by engineers in renovation and remediation projects in various buildings across the UK.

The technology

The objective of polymer ground engineering technology is to improve the load-bearing soil structure beneath foundations. This is achieved through the controlled introduction of a suitable consolidating agent, specifically applied to the area where there are geotechnical problems. This is accomplished by using patented injection technology, known as the Deep Injection Method or System. The geotechnical difficulties that have to be overcome result from foundation soil weakness (see Figure 1). This may be initially structural, such as lack of compaction, or caused through such external forces as flood, movement, or washout. Evidence of such foundation defects is usually indicated in existing structures by dropped or cracked internal or external walls, misshapen window frames and lintels, doors and door frames which no longer fit.

Group research and development

Uretek companies operate throughout the world and operate a polymer research and development facility in Italy. This has resulted in development of specific and unique geo-polymer products, the most recent of which is Geoplus, used in 90% of Uretek's deep injection work.

Technical characteristics

It is important to understand that consolidation characteristics of this product are subject to load. When injected under foundation loadings, the compressive strength of the material is similar to a typical concrete mix. It provides thrust up to 2500kN/m^sup 2^ beneath walling (see Figure 2). This has been used to lift very substantial buildings, for example high-rise apartments and ancient stone castle walls. Such remediation has been achieved through a single application of the deep injection method, the technique being used without extensive ground excavation or disruption to structures.

Deep injection method

The geo-polymer injection method is specific and proven. It involves using several polymer injection points, typically at 1m intervals, into the areas of weak subsoil at the points of load. Each group consists of three or four drillings, determined by the geotechnical analyses, to depths of 1, 2, 3, and 4m. A measured length of 15mm diameter copper tube is inserted to its full depth. Liquid polymer in two components - resin and catalyst - is injected through these tubes until the necessary lift has occurred. This system enables the precise placement of geo-polymer at several depths, thereby providing consistent ground consolidation, lifting and levelling of the building structure by a precise amount. The material migrates through voids and soil particles to form a dense, stable matrix.

The polymer reaction occurs extremely quickly, which avoids unwanted material spreading into areas not requiring treatment. The material is also hydro-insensitive. The increased load-bearing capacity of weak foundation soils can be demonstrated through standard dynamic probe tests (DPT) before and after treatment.

Three case histories

The following three case histories from recent and current projects demonstrate the varied projects for which the technique may be used. These examples demonstrate foundation strengthening for additional loadings, ancient monument remediation and application of the system to provide additional load-bearing capacity for a brand new complex.

Increased load on Hoxton property

The client required the addition of a one-storey penthouse to a three-storey terraced property off Old Street, London. This necessitated increasing the foundation load-bearing capacity. This double-fronted unit features retail/commercial space on the ground floor. The foundation soils consisted of artificially consolidated ground above levels of sand and gravel. Soil investigations indicated the requirement for considerable additional densification to achieve the necessary increase in load-bearing capacity. The system was used beneath the front elevation and internal spine wall, now formed by support pillars. DPT testing was undertaken after the treatment, thereby proving that the soil would withstand the additional loading (see Figure 3). The consulting engineers were Howard Cavanna.

Ruins in the Prime Minister's constituency

In a project championed by Tony Blair, Durham County Council has undertaken the restoration of a gothic ruin on the Hardwick Park Estate (see Figure 4). This tower originally rose to a height of 16m. It was constructed 250 years ago in local stone to provide views over the parkland. However, time has had a severe effect and original foundations were inadequate. After treatment, Deep Injection trials and DPT testing during 2003 indicated a 100% increase in consolidation to a depth of 4m. Treatment for the whole tower foundation is now planned. The 120mm lean from plumb will then be corrected and building works undertaken to restore the tower to its original height. Professional advisors to the scheme are John Niven Architects and BDN Consulting and Civil Structural Engineers, Durham.