Piling

Bachy Soletanche is a leader in piling solutions, providing a vast range of techniques and using a fleet of specialist rigs to providing.

Bachy Soletanche is one of the UK’s leading foundation and underground engineering specialists with a reputation for the delivering high quality, cost effective, sustainable, and innovatively designed geotechnical solutions to budget, on programme, in a safe and efficient manner.

Rotary Bored Piling

Bachy Soletanche defines piles in excess of 600mm diameter to be large diameter.

L.D.A. rigs tend to be higher power (torque) than CFA rigs are more able to over come underground obstructions. Rotary piles have the ability to: quickly change coring or digging tools and auger type; have plunge columns installed into them; be under-reamed to facilitate higher base capacity. Bored rotary piles also have the advantage of having the reinforcement cage installed into the open bore, and so can accommodate full length reinforcement.

We have the capabilities to produce piles up to 2800mm in diameter and to depths up to 66m. Large diameter piles can carry significant loads, both in end bearing and from skin friction.

The process for the construction of large diameter rotary bored piling in general terms comprises of the following steps as shown below.

The installation process of LDA piling

rotary-illustration

CFA Piling

CFA (Continuous Flight Auger) piles are quick to install and offer an efficient, rapid solution for predominantly more lightly loaded structures.

Bachy Soletanche have a large fleet of C.F.A rigs, in a variety of sizes to offer clients the best value, for a large variety of piling projects. Our highly experienced in-house design and pre-contracts teams, are based throughout the U.K., and so have an in depth knowledge of the most cost effective foundation systems.

Recent advances in rig technology have lead to, in the right soils, larger diameters up to 1200mm, or longer piles up to 32m, being installed. Quality has also been improved in recent years with our skilled and experienced site staff and sensitive onboard instrumentation, to monitor performance and quality.

This enables Bachy Soletanche to offer the best value CFA piles at first time of asking.

The installation process of CFA piling

cfa-illustration

Rotary Displacement Piling

Rotary displacement piling systems provide improved soil strength, pile capacity and load transfer to the surrounding ground.

The technique also offers a reduction in overall foundation costs by reducing pile lengths and diameters and most significantly, substantially reducing/eliminating the cost of pile spoil disposal.

As the boring tool penetrates, soils are displaced resulting in a localised, increased relative density and strength around the pile (depending upon soil conditions). Minimal spoil comes to the surface.

Improved load transfer to the surrounding ground is achieved through an enhanced shaft capacity. Thick concrete threads are created in the construction process that facilitates the load transfer from pile core to soil. This is achieved through the creation of an increased diameter/surface area and the bearing effect of the thick threads formed.

Minimal spoil at ground level provides an ideal solution for Brownfield sites where contamination may be an issue.

Restricted Access Mini Piling

Where access is restricted or heavy plant is prohibited, foundations may be constructed by the use of mini piles which provide an efficient alternative with minimal vibration.

Mini piles can be constructed in under 2.8m of headroom in a variety of sizes and within 400mm of existing walls. They can also be installed through basements and old foundations.

Digital instrumentation on drills monitor changes in ground conditions and protect sensitive structures.

Our patented TMD system can also be utilised in many cases to greatly increase the load carrying capacity of mini piles. This can achieve working loads of 1000kN with settlements of less than 10mm.

Retaining Walls

Bachy Soletanche has extensive experience in the design and construction of structural retaining walls for all temporary and permanent requirements.

Our expertise spans a wide variety of ground conditions, in both urban and green field environments.

Bored pile walls (contiguous or secant) can be the ideal solution for more restricted sites when the wall is constructed using continuous flight auger techniques or with temporary casings.

We have designed and built a number of hybrid retaining walls in appropriate ground conditions as cost effective alternatives to sheet piling.

Bored piles can be constructed through bentonite cement slurry with lateral loading on the wall carried by “arching” between the bearing piles. This can provide a very reliable temporary works solution.

A variation of this technique was developed by our engineers for shaft construction on the Copenhagen Metro Project, using sheet piles driven within a bentonite cement slurry.

Retaining Wall Systems

retaining-walls

Bored Pile Walls

Bored pile walls (contiguous or secant) can be the ideal solution for more restricted sites when the wall is constructed using continuous flight auger (CFA) techniques or large diameter auger (LDA) with temporary casings.

We have designed and built a number of hybrid retaining walls in appropriate ground conditions as cost effective alternatives to sheet piling. Bored piles can be constructed through bentonite cement slurry with lateral loading on the wall carried by “arching” between the bearing piles. This can provide a very reliable temporary works solution.

Diaphragm Walls

Diaphragm walls provide rigid, cost effective solutions for permanent retaining walls and shafts, with less construction joints than bored pile walls. They are particularly suitable for large, more open sites where structures greater than 25m deep are required.

The Diaphragm walling technique offers improved verticality tolerances to CFA and rotary bored piling, up to 1:400 for Hydrofraise, and delivers a smoother finish. Water tightness is normally delivered using a CWS water bar between the diaphragm wall panels.

Present day methods of constructing diaphragm walls – by using a bentonite powder mixed with water suspension (slurry) to support and stabilise the trench walls during excavation – have been adapted from the drilling techniques employed by oil well engineers.

We have developed a range of construction techniques and components in this field including CWS watertight seals, rope suspended grabs, KS3000 hydraulic grabs for increased production and verticality control, and Hydrofraise reverse circulation excavation rigs (including compact models). This excavating equipment works quickly and effectively through the viscous slurry whilst maintaining accuracy of alignment both vertically and between panels.

For rock and deep walling applications, Hydrofraise drilling machines are utilised. The use of the Bachy Soletanche patented CWS Stop End incorporating a waterbar, ensures maximum water tightness between adjoining panels.

Diaphragm walls are constructed as permanent walls, which reduces the width of construction and working space required when compared to a solution that has both a temporary ground support and permanent works within.

Walls can be made extremely stiff and therefore better resistant to deflection. It is also possible to use effective internal propping with a diaphragm wall rather than the normal ground anchors. Temporary cut-offs can also be created using this technique.

The installation process of Diaphragm Walls

DwallDwg

Secant Walls

Bachy Soletanche is experienced in designing and building hard/soft, hard/firm and hard/hard secant walls using continuous flight auger techniques or segmental casings for applications of 750mm pile diameters upwards.

The development of powerful high torque drilling equipment has led to an increase in the range of ground conditions and obstructions that can be penetrated and the wall thicknesses that can be constructed. We are therefore able to install secant walls in the most challenging urban environment.

Where soils are saturated and water tightness is a requirement, secant walls using either bentonite cement materials (soft) or weaker concrete (firm) are used in combination with reinforced concrete (hard) piles. These alternatives are generally used where temporary works are required.

Permanent retention can be provided with all reinforced piles (hard/hard), which can be incorporated within the final structure.

Piles in a secant wall are spaced at 0.8 to 0.9 pile diameters. Primary piles are secanted by secondary piles, thus providing a closed structure to act as a barrier in water bearing soils, and to prevent the ingress of soil between the piles.

Secant piling offers minimal vibration, low noise levels and the flexibility to fit complex site boundaries to maximise land use. Secant piling also has the ability to go through underground obstructions such as steel, heavily reinforced concrete, granite and masonry, while at the same time, avoiding any risk of construction induced settlements to neighbouring structures.

Contiguous Walls

In dry stable soils, contiguous bored pile walls can be constructed.

This type of wall is a series of piles with intervening gaps which provide an effective retention solution. Individual piles are spaced at 1.1 to 2 piles diameters apart in a phased sequence.

Cased Secant Piling (CSP)

Secant piled walls are generally a preferred solution for inner city projects. The reasoning is that they can be more flexible in shape and a compact operation when compared, for example, with diaphragm walling (this also requires a bentonite plant).

The interlocking piles of a secant wall can also form a closed structure to act as a barrier in water bearing soils.

The CSP system has been developed to combine the more cost-effective CFA technique with temporary casings that are more traditionally associated with rotary bored piling methods.

The CSP system generally has the following advantages:

  • Better tolerance than an uncased CFA secant wall.
  • Better ultimate appearance and reduced overbreak than an uncased CFA secant wall.
  • Speedier operation than the more traditional ‘kelly / casing’ rotary bored pile method.
  • Reduced risk of ‘flighting’ in poor soils than a standard CFA system.
  • As it is a cased system; it reduces the risk of distress to adjacent structures in certain soils like sands or gravels.

In general terms, whilst the CSP process does have limitations with respect to diameter and depth, it will generally give the client a better assured product in terms of vertical tolerance and visual appearance.

Grouting

Grouting involves the injection of a pumpable product (slurry), which will subsequently stiffen, into the soil or into man-made material (masonry), in order to consolidate the soil or structure or make it impermeable, through filling all the voids it contains.

The slurry can fill the voids in the ground, the cracks within rock, solution cavities (it is then referred to as fissure and permeation grouting) and/or displace the surrounding soils through a bottom-up process or by fracturing (compaction grouting or solid injection – see the section on the subject – and strain injection). Grouting with soil displacement may be used to prevent potential damage to the structure brought about by excavations (galleries and tunnels, major urban excavations, etc.) and this is called compensation grouting (see the relevant section).

Quality control during grouting is a key success factor for successful completion of the process. Soletanche Bachy has its own in-house control system, called SPICE (and GROUT I.T. in the USA), the development of which started in the 1980s. The system drives the vast amount of data required for each grouting operation, at every level of production: the setting-up stage (borehole geometry and the calculations of the volumes of grout needed) the acquisition and injection settings, controlling the grouting plant (monitoring the pumps, acquiring flowrate and injection-pressure data), and tracking quality and production.

grouting

The software package developed by Soletanche Bachy comprises a suite of interactive programmes:

  • CASTAUR groups together all the exploration data and establishes the location of grout holes.
  • SPICE is installed in the grouting plant and controls all grouting operations, including the electro-hydraulic grouting pumps.
  • SPHINX organises all the grouting data and presents them in a graphic format.

The advanced features of this package make it enormously helpful in the grouting process:

  • Safety, data collection and subsequent control of operations in the field are extremely precise and rigorous.
  • Quality: powerful synthesis and analytical tools produce fast, automatic reports and diagrams ;
  • Performance: higher productivity, along with efficient control that fits in with the increasingly high turnaround rate.

 

Jet Grouting

Jet grouting is a construction process that uses a high-pressure jet of fluid (generally 20 – 40 MPa) to break up and loosen the soil at depth in a borehole and to mix it with a self-hardening grout to form columns, panels and other structures in the ground.

The parameters for the jet-grouting process and the desired final strength of the treated soil depend on a number of characteristics, such as the soil type, the technique used and the objective to be reached. In granular soils, the high-pressure jet breaks up the grains through erosion, while in a cohesive soil, such as clay, the jet breaks the mass up into small particles. High pressure is needed to produce the kinetic energy required for the jet through a small-diameter nozzle. Waste material from the process (a mix of soil, water and binder) is recovered at the surface before being taken away for disposal.

Three basic jet grouting systems are currently used:

SINGLE JET
Soil loosening and grout injection are performed by a jet of high pressure grout from nozzles at the bottom end of a drill rod.

TWIN JET
Soil loosening and grout injection are performed by a high pressure jet of grout shrouded by a concentric jet of air which increases the radius of action.

TRIPLE JET
Soil loosening is performed by a jet of water shrouded by concentric jet of air. Grout injection is performed by a separate jet of grout.

The process can be used in all loose or soft-rock soils to reinforce them or, in certain cases, to make them impermeable: underpinning buildings, dam cut-off wall, excavation retaining wall, pipe roofing for tunnels, with possible reinforcement of side-walls, etc.

When jet grouting is used for soil impermeability, it is sometimes necessary to use an additional grouting treatment, depending on the required final soil properties.

Download the Jet Grouting Brochure:

Injection Grouting

Injection grouting is just one of the major techniques that Bachy Soletanche is able to offer in the complex field of ground improvement.

The main categories of injection grouting available are:

Permeation Grouting
Grout filling of accessible pores between the solid particles in a permeable soil. This technique is generally used to reduce permeability and/or to strengthen and stiffen the ground.

Hydro Fracture Grouting
Involves the deliberate fracturing of the soil or rock by grout under pressure. The resulting compaction and stiffening of the rock or soil mass can, in appropriate conditions, provide ground improvement where permeation grouting is not practicable.

Compensation Grouting
An active technique to mitigate settlement arising from other engineering works (such as tunnel excavation) in order to provide protection to existing structures. Compensation grouting can take the form of permeation, compaction, or hydro fracture grouting depending on the local conditions of the given project.

Compaction Grouting
The injection of stiff mortar or paste instead of grout to displace and compact the soil in situ, thus improving its engineering characteristics.

Rock Grouting
Grout infilling of discontinuities, fissures, fractures or joints in mass rock with the intention of reducing permeability and increasing the competence of the mass rock. This technique is particularly employed for dam construction and tunnelling.

The injection methods that can be employed for the above techniques range from packer injection via a Tube a Manchette (TaM), packer injection direct into rock, descending / assecending, stage grouting or grout injection direct via drilling tools (end of casing grouting) or lancing.

Anchors

Bachy Soletanche has many years experience in the design and installation of soil and rock anchors.

Ground Anchors

A ground anchor is a load transfer system designed to transfer the forces applied to it to a competent stratum. An anchor is said to be temporary if it has a lifespan of under two years and permanent if the lifespan is over two years.

An anchor comprises three parts:

  • The head, transmitting the anchor force to the structure via the bearing plate.
  • The free length of tendon, from the head to the near end of the anchorage.
  • The grouted anchorage, which is the length of tendon by which the tensile force is transmitted to the surrounding ground through the grout.

ground-anchors-diagram

There are “active” and “passive” soil anchors:

  • A passive anchor is only tensioned by the structure itself applying load to it. It does not usually have a free length of tendon. Generally speaking, the tendon is made of steel or an alloy. An anchor is said to be temporary if it has a lifespan of under two years and permanent if the lifespan is over two years
  • An active anchor is pre-tensioned before it takes up the load, which prevents distortion of the structure. The tendon is usually made of pre-tensioned steel cables.

Soil Nailing

Soil Nails provide a wealth of advantages over other slope stabilisation methods. Half the cost and twice as quick to install as concrete piled retaining walls, they can be used to form steeper slopes than an engineered embankment.

Tendons are inserted into a nominally 115mm diameter hole which is then tremie grouted. As the nails are designed to act as a composite system they are connected by a geogrid which covers the entire slope and is fixed using concrete plates with the tendon secured using a wedge grip mechanism.

Environmental Engineering

Bachy Soletanche has a wealth of experience, throughout the world, in applying novel solutions to the containment and/or treatment of contaminated soil and groundwater. Those solutions are the result of a unique combination of unrivalled geotechnical and geo-environmental knowledge and our ongoing research and development programme.

Slurry Wall Cut-Offs
Slurry walls are an effective means of preventing the mitigation of water, contaminated water and leachate.

We use a variety of excavation techniques, depending upon depth and ground conditions, and employ a bentonite cement slurry mix to stabilise the trench and form the permanent cut-off wall.

The thickness of the wall is normally 600mm, but this can be increased to 1.5m if necessary.

Slurry Walls with HDPE Membrane
For situations demanding increased security, such as containment of landfill gas, or where post construction ground movements may be significant, a high-density polyethylene membrane can be included in a standard slurry wall.

This technique has been applied to depths up to 32m.

The membrane is installed into the slurry trench, before setting, on frames between 2m and 6m wide. The frames are withdrawn from the trench leaving the membrane in position. Panels are jointed in the trench using “Geolock” interlocking clutches incorporating Hydrotite.

Thin Cut-Offs by Vibwall
A Vibwall is ideal for creating cost effective, temporary isolation cells, where groundwater or soil can be decontaminated. Heavy H-shaped lances equipped with grout pipes are driven into the ground and grout is injected to leave an H-shaped grout column. The lance is then re-driven in successive positions to create a continuous wall generally between 60mm and 80mm thick. In suitable ground the technique can achieve a depth of 25m.

Landfill Gas Venting
Gas relief wells control the migration of landfill gases by drawing them out from the body of the tip, or by intercepting lateral spread.

The location, arrangement and interlinking of the boreholes are carefully designed to provide active or passive extraction systems and for larger sites, there is the possibility of harnessing and utilising the energy of the landfill gas.

Cut-Offs by Soil Mixing
The Cutter Soil Mixing (CSM) wall provides a cost effective solution for the rapid construction of retaining and cut-off walls by mixing soil in situ with a cement / bentonite grout.

Like traditional walls, the CSM wall consists of adjacent male and female panels, with thickness typically ranging from 500mm to 1000mm.

Depending on soil conditions and specific project requirements, the soil is mixed and grouted, following pre-determined procedures during the drilling and the extraction phases.

Soil Mixing
Soil mixing can also form vertical containment barriers. Traditionally this has been carried out by mixing vertical columns (utilising either single or multiple augers) which are overlapped to form the barrier. Techniques using this method include Colmix and Trenchmix.

Permeable Reactive Barriers
We are leading providers of “active” barriers, which allow the passage of groundwater with simultaneous decontamination. These barriers can be either continuous or with defined flow paths that can be engineered to control and monitor the treatment process more effectively.

Our innovative, patented “Panel Drain” system can be easily incorporated into slurry walls to provide “gates” where inflow and outflow quality can easily be monitored, and the reactive material replaced or regenerated as necessary.

This solution is ideal for working sites, providing insurance against future contamination and supporting pollution containment or gradual cleanup.

Treatment of Contamination
Treatment can be carried out on site using either ex-situ or in-situ methods to chemically stabilise and/or solidify contaminated ground or waste. Desk studies, laboratory trials and full scale trials are carried out as necessary to ensure that the treatment will be effective.

In-situ treatments can be applied using the patented Colmix process, which utilises overlapping contra-rotating augers to introduce and fully mix the reagents and soil whilst compacting to minimise volume increases.

Ex-situ treatments are carried out with a range of equipment specifically selected to provide cost effective and efficient solutions in each and every case.

Design

The vast majority of projects carried out by Bachy Soletanche are undertaken on a design and build basis with the design element carried out in-house by a group of fully qualified technical staff.

All senior design staff have site experience at contract management level and are therefore conversant with the relevant construction processes. They are aware of the inherent risks.

In addition to preparing final working designs for contracts that have been won, many detailed design alternatives for projects are prepared as part of the normal tendering process. It is this approach which often gives our tendering a competitive edge, leading in many cases to success in a very competitive market.

Design engineers work closely with estimators and operations staff at tendering stage to ensure that technical optimisation is related to economic efficiency and operational practicality. During the tendering process, the designers develop an understanding of the performance requirements as well as a realistic assessment of the ground conditions. In addition, technical, environmental and operational risks are evaluated at this stage.

By utilising our design resource to develop solutions that are technically sound, practical to construct and economically attractive, we are able to offer cost effective solutions to our clients together with an appropriate evaluation of risk. It is this approach which makes our design expertise one of the company’s key strengths.

We are constantly involved with the latest CDM regulations for all design and construction works. Potential hazards associated with the geotechnical processes are highlighted to clients for incorporation into health and safety plans.

Due to the nature of the works, our designers follow the works through the construction phase. Any new hazards will be identified and additional risk assessments carried out where hazards are not covered in our original risk assessments for the regularly used geotechnical processes and materials. These further risk assessments may be, for example, a function of the site size, geometry, geology, location or specified materials used or encountered.