Chris Gorse Advanced Construction Technology By Professor Chris Gorse & Ian Dickinson – licensed under the Creative Commons Attribution – Non- Commercial – Share Alike License

Ground and soil stabilisation Chris Gorse and Ian Dickinson These slides should be read in conjunction with Emmitt, S. and Gorse, C. (2010) Barry’s Advanced Construction of Buildings. Oxford, Blackwell Publishing

Chris Gorse General problems of ground instability include: Landslip Surface flooding and soil erosion Natural caves and fissures Mining and quarrying Landfill Natural geological variation – faults, changes in geology – differential settlement

Chris Gorse Improving the ground There are a number of different methods that can be used to increase the strength and stability of the ground.

Chris Gorse Ground stabilisation Dynamic compaction Vibro compaction - Vibro displacement Vibro flotation - high pressure water jets (improves penetration of hard substrates) Pressure grouting Surcharging Geotechnic membranes Soil modification and stabilisation

Chris Gorse Dynamic compaction This involves dropping heavy weights onto the ground. The weight causes the ground to compact.

Chris Gorse Dynamic compaction Ground is consolidated by repeatedly dropping dead weights and specially designed tampers Weights include: Flat bottomed and cone tampers Traditional weights are flat bottomed with cable Modern systems use cones with guide rails Dynamic compaction is suitable for granular soils, made-up and fill sites Using dynamic compaction bearing capacities of 50 to 150kN/m 2 can be achieved

Chris Gorse Dynamic compaction

Chris Gorse Dynamic compaction – compaction plan (adapted from Plan

Chris Gorse Typical cone type tampers (adapted from bullivant.co.uk)

Chris Gorse Dynamic compaction rig

Chris Gorse Vibro compaction or displacement Vibrating rods are forced into the ground causing the surrounding ground to compact and consolidate.

Chris Gorse Vibro compaction or vibro displacement Vibrating mandrels (poker, shaft or rod) penetrates, displaces and compacts the ground. Void Created is filled with stone and recompacted Produces stone columns in the ground, compacts surrounding strata enhancing the ground bearing capacity and limiting settlement Typical applications include support of foundations, slabs, hard standings, pavements, tanks or embankments.

Chris Gorse Vibro compaction - continued Used in soft soils, man made and other strata, can be reinforced to achieve improved specification On slopes it can limit the risk of slip failure. Ground bearing capacities, for low to medium rise buildings and industrial developments, is in the region of 100kN/m 2 to 200kN/m 2. Improved ground conditions may allow heavier loads to be supported. Used in granular and cohesive soils

Chris Gorse Benefits of vibro-compaction Buildings can be supported on conventional foundations (normally reinforced and shallow foundations). Work can commence immediately following the vibro displacement. Foundations can be installed straight away. The soil is displaced. No soil is produced. Contaminants remain in the ground – reduces disposal and remediation fees. Economical, when compared with piling or deep excavation works. Can be used to regenerate brownfield sites Can use reclaimed aggregates and soils.

Chris Gorse Vibrofloatation Vibro floatation uses a similar process to vibro compaction Water jets at the tip of the poker Water jets help the vibrator penetrate hard layers of ground Major disadvantage is that the system is messy and imprecise, thus rarely used

Chris Gorse Vibro displacement - Typical sequence

Chris Gorse Vibro displacement - Typical sequence

Chris Gorse Mandrel positioned ready to compact and displace

Chris Gorse Ground displaced

Chris Gorse Ground compacted void remains

Chris Gorse Void filled with stone

Chris Gorse Hardcore is repeatedly displaced and compacted

Chris Gorse

Grouting Grouting may be used to fill the voids in the ground increasing the strength of the ground.

Chris Gorse Pressure grouting In permeable soils, pressure grouting may be used to fill the voids. Holes drilled using mechanically driven augers. As the auger is withdrawn cement slurry is forced down a central tube into the bore under pressure. Pressures of up to 70,000 N/mm 2 can be exerted by the grout on the surrounding soil. Slurry contains cementious additives, e.g. pulverised fuel ash (pfa), microsilica, chemical grout, cement or a mixture.

Chris Gorse Pressure grouting In weak soils it will displace and compact the ground as it fills the voids. Ground becomes stiffer, more stable and water resistant. Pressure grouting can also be used around basements and cofferdams to reduce the hydrostatic pressure on the structure.

Chris Gorse Pressure grouting To create a water resistant barrier the bores and subsequent columns of grout are placed at close centres. PFA is generally used as the ground modification and stabilisation material Expensive chemical mixes (resin or epoxy mixes) or those containing microsilica are used to fill small voids and improve the grounds water resistance.

Chris Gorse Soil modification and stabilization Machines are available that can break-up the ground, mix the ground with new cementious material and improve the ground quality.

Chris Gorse Soil modification and recycling Plant has been developed that is capable of cutting into the ground (including contaminated material), breaking up the strata, then grading and crushing the material before mixing it with cementious additives and relaying This provides a compacted modified or stabilised hard standing.

Chris Gorse Soil modification and recycling A large cutting wheel that brakes down and pulverises the soil. Soil graded and additives introduced in mixing chamber. In cohesive soils, quicklime is most commonly used as the additive In granular soils the additives are usually cement, microsilica or pulverised fuel ash. Only small dose of additives are needed to stabilised soil to provide a workable strata

Chris Gorse Soil modification and recycling Additives used in soil stabilisation increase the strength better, improve compacted and maximise bearing capacity and minimise settlement. The technique can be used to provide stabilised or modified materials for earthworks, or may be used to provide permanent load transfer platforms or hard standings. Can be used to treat and neutralise certain contaminants or encapsulate the contaminants, removing the need for expensive removal and disposal.

Chris Gorse Soil modification, stabilisation and recycling machine

Chris Gorse Schematic of soil modification and mixing chamber

Chris Gorse Soil modification and stabilization rig www. roger-bullivant.co.uk

Chris Gorse Soil modification and stabilization plant www. roger-bullivant.co.uk

Chris Gorse www. roger-bullivant.co.uk

Chris Gorse Soil modification and stabilization plant www. roger-bullivant.co.uk

Chris Gorse Surcharging This involves placing heavy loads on the ground for long periods of time. Over time the ground will compact. Surcharging is time consuming and ties up the land Can be used if long lead-in time available Can be used on roads May be used on investment land (land bank). The increase in strength will increase the value of the land.

Chris Gorse Surcharging Excavated material, quarried stone or other heavy loads. Settlement and compaction period 6 months to a few years. For economics the surcharging acts as a temporary storage facility

Chris Gorse Geotechnical membranes Geotechnical membranes provide a sheet of reinforcing material that can be added to the ground. This increases the stability and tensile strength of the ground.

Chris Gorse Geotecnic membrane

Chris Gorse Geotechnical membranes Natural Plastic manmade Built up in layers compacted between ground hardcore Sheets, fibres and strips

Chris Gorse Further information supporting these slides can be found in the following publication and websites. Emmitt, S. and Gorse, C. (2010) Barry’s Introduction to Construction of Buildings. Oxford, Blackwell Publishing Emmitt, S. and Gorse, C. (2010) Barry’s Advanced Construction of Buildings. Oxford, Blackwell Publishing Virtual Site (2010) Virtual Site at Leeds Met University Virtual Site Gallery (2010) Virtual Site Gallery at Leeds Met University