Ground Improvement Techniques

Category

Densification

Consolidation

Function Increase density, bearing capacity, and frictional strength; increase liquefaction resistance of granular soils; decrease compressibility, increase strength of cohesive soils

Accelerate consolidation, reduce settlement, increase strength

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Load Reduction

Reduce load on foundation soils, reduce settlement, increase slope stability

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Reinforcement

Inclusion of reinforcing elements in soil to improve engineering characteristics; provide lateral stability

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Methods Vibrocompaction M1:Dynamic compaction M2:Geopolymer Injections Blasting compaction Compaction grouting M4:Surface compaction (including rapid impact compaction) Preloading without drains M3:Preloading with vertical drains Vacuum consolidation Electro-osmosis Geofoam Foamed concrete Lightweight fills, tire chips, etc.

Mechanical stabilized earth Soil nailing/anchoring Micro piles Columns (aggregate piers, stone columns, jet grouting, etc.) Fiber reinforcement Column supported embankments with load transfer platforms Geosynthetic reinforced embankment

M1

The Dynamic Compaction technology, also known as dynamic consolidation

The basic principle behind the Dynamic Compaction (DC) technique consists in the transmission of high energy waves in order to improve weak subsoil. As a result of the impact the soil is compacted depending on its condition, structure and depth. The energy is transferred to the subsoil by multiple impacts with properly shaped weight (normally steel pounder) with a weight ranging from 10 to 40 tons free falling from a height ranging from 5 to 40 m. In order to perform an effective dynamic consolidation the lattice - boom cranes are used obtaining sufficiently high impact energy. The Dynamic Compaction method consists of two pounding stages where in the first stage deep layers are compacted and in the second stage intermediate layers. After completion of the two stages the surface compaction (so-called 'ironing') is carried out within the entire improved area. The Dynamic Compaction is normally preceded by the development of a test plot where the grid spacing is determined along with the impact energy which is needed to achieve the required compaction, i.e. weight and shape of the pounder and the height of its drop.

M2

Geopolymer Injections

If the soil is not stable and strong enough, there is a risk that the building or structure may subside. URETEK has a solution to improve and stabilise the ground and the bearing capacity directly under the foundation without excavation, vibrations or other disturbances. The method uses geopolymer which is injected deep into the ground, where it expands and reaches a force of up to 10,000 kilopascals. When the geopolymer expands, it makes the surrounding ground denser and thus prevents the building or structures from subsiding and settling. With URETEK ground improvement the bearing capacity can be improved in advance, for example when a building's usage changes and it’s  likely that the load on the building will increase. Geopolymer injections and URETEK ground improvement can be used in almost all types of soils and can be used to stabilise a variety of different buildings, such as industrial and commercial buildings, car parks and roads. If needed, the structures can also be lifted back to the desired level with millimetre precision. Before the repair work begins URETEK’s team carefully investigate the soil u nder the foundation. The results of the test will show how deep the geopolymer should be injected and which types of geopolymer should be used to maximise the bearing capacity of the ground. When you know the soil conditions, small holes are drilled through the foundation or the slab. Injection tubes are installed into these approximately 2cm d iameter holes. Through these tubes the geopolymer is injected as deep as is necessary. Firstly the geopolymer, which is in liquid form, penetrates the voids that are in the soil and thereafter expands and seals the surrounding soil.

The injection process is monitored by laser, which indicates when the soil has reached the desired bearing capacity. The geopolymer that is injected in the soil hardens in about 15 minutes, and the desired bearing capacity of the structure is reached. Benefits of ground improvement    

The ground can be improved and stabilised quickly and non-disruptively In smaller projects the ground and the soil can be improved and stabilised in a few hours If necessary, you can inject geopolymer on a small, enclosed area The geopolymers that URETEK use are safe and proven, don’t dissolve in water or give extra load to the surrounding soil and ground.

M3

Preloading with vertical drains

Vertical Drains, also known as Wick Drains or Band Drains, are used to accelerate the consolidation of embankments built of fine grain soils. This is normally to expedite construction and limit long term settlement.

The construction of a new embankment or structure induces additional stresses on the ground that can create unacceptable long term settlements during the life of an embankment or structure. A preloading programme can be designed to induce these settlements in an accelerated time frame and minimise the long term residual settlements to be within acceptable limits.

Fine grained soils such as Clays and Silts are usually saturated and therefore, settlements can only occur if the excess water is expelled through the voids in the soil grains and particles. These soils also tend to have a low permeability, and so the reduction of pore water pressure can be a slow process.

Vertical drains consist of a flat or cylindrical plastic core wrapped in a geotechnical fabric, and allow water to drain up through the centre of the drain. These come in a variety of sizes and shapes to meet a variety of soil and site conditions.

Vertical drains can be used to increase the rate of consolidation, delivering substantial  programme savings for the build times of earth embankments for many types of land raising schemes.

Prefabricated vertical drains are installed by pushing a ho llow steel mandrel, which house the drain material, and are set out on a grid pattern. The mandrel is driven into the ground by the rig, once at the required depth the mandrel is removed, leaving the vertical drain anchored by a steel anchor plate that holds the drain securely in place. The mandrel can penetrate soils up to a tip resistance of 5MPa, firmer soils can be p enetrated by the use of vibrators or pre-drilling. A temporary surcharge embankment needs to be combined with the installation of the Vertical Drains in order to expedite full or partial primary consolidation, as well as induce several years of secondary consolidation settlement. Placement of the embankment and the additional temporary surcharge embankment are placed in phases, to avoid the risk of slip failure.

Real time monitoring of the geotechnical parameters, including pore pressures and horizontal displacement, are monitored throughout the consolidation p eriod. These instruments are installed to validate the design and the safe phasing of the embankment construction. These results will also be used to back analyse the design and access the consolidation process

M4

Surface Compaction

Backfilling material

Compaction