Walls Datasheets Diaphragm walls Slurry trench Bored pile walls
Diaphragm Walls Technical Data Application Diaphragm walls can be used in most ground conditions to construct deep basements, underground tanks, access shafts, road and rail underpasses and tunnels where open cut and cut & cover techniques are commonly used. Diaphragm walls are often located in confined inner-city areas where space is at a premium. Particular applications of diaphragm walling include construction of underground stations in city centres, multi-level underground car parks, road junctions and underpasses, and open cut and cut & cover rail tunnels as well as deep shafts for tunnel ventilation and intervention shafts, and water treatment plants. Diaphragm walls are typically constructed in reinforced concrete to provide the required structural capacity, but they may also be designed as unreinforced plastic cut offs (or slurry walls) to stop water flow through porous strata. Diaphragm walls are typically 20m to 50m deep, but may extend to considerably greater depth. Advantages Box outs can be incorporated in diaphragm walls to facilitate easy connections for slabs, stairs, etc Waterbar can be incorporated Less joints required than a piled wall Top-down basement construction gives significant advantages in programme Trademark CEMLOC Patents UK Patent No. 271069 Europe (DK, FI, IE, IT, NL,SE) Pub No. 122248 Hong Kong Pub No. 1045720 USA Patent No. 679805 USA Pub No. 200211901 Diaphragm walling refers to the in-situ construction of vertical walls by means of deep trench excavations. Stability of the excavation is maintained by the use of a drilling fluid, usually a bentonite suspension. The walls are constructed in discrete panel lengths ranging typically between 2.5m and 7.0m using purpose built grabs or, in appropriate circumstances, milling machines (hydromills). Excavation is typically carried out using either rope-suspended mechanical or hydraulically operated grabs. Standard grabs range in weight from 8-20 tonnes. The grabs are mounted on 80-120 tonne hydraulic base crane units providing stability and suitable line pull. Specific applications and ground conditions demand the use of hydromills hydraulically operated reverse circulation trench cutters where the excavation technique is by cutting as opposed to digging. This technique is appropriate for deeper diaphragm walls and walls located in granular materials and soft rock. Where panels are constructed in a line, abutting one another to form a retaining wall, the term diaphragm walling applies. Purpose made stop ends are used to form the joints between adjacent panels and a water bar can be incorporated across these joints. Where additional bending moment capacity or wall stiffness is required more complicated arrangements can be constructed, e.g. L shaped or T shaped panels. Standard widths of diaphragm walling equipment are 600, 800, 1000, 1200 and 1500mm although greater can be provided. Depths are typically constructed up to 50m using grabs and up to 80m using standard hydromills. One significant advantage of using diaphragm walling is the facility to incorporate floor slab connections and recessed formwork into the walls. Verticality tolerances are typically up to 1:200 and onboard monitoring is now available to provide real-time monitoring of excavation accuracy. 08/08/07 Rev 2
Diaphragm Walls Further information Cementation Skanska Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD 9SW United Kingdom Tel: +44 (0)192 42100 Fax: +44 (0)192 42681 cementation@skanska.co.uk www.skanska.co.uk Offices Head Office +44 (0)192 42100 North +44 (0)102 821100 South West, Midlands & Wales +44 (0)1454 45200 Scotland +44 (0)1698 75899 Northern Ireland +44 (0)28 9024 2746 Republic of Ireland +5 (0)1296 0790 Management of the bentonite or alternative drilling fluid requires controlled use of specialist desanding, desilting and centrifuge equipment. Unit capacities range from 100 to 500m /hour. Diaphragm walls are particularly suited in the construction of deep basements when used in conjunction with top down construction techniques. The top down method of construction is designed to enable above ground construction work to be carried out simultaneously with the excavation of the basement resulting in significant saving of time on a project. The technique can be further enhanced when columns are accurately installed into bearing piles, cut off below basement slab level. The Copmany s unique CEMLOC device enables steel columns to be plunged and accurately located into piles to structural engineering tolerances, even when the piles are constructed using drilling fluid, such as bentonite. Barrettes The term barrette refers to individual foundation panels constructed by the above techniques. Barrettes are effectively rectangular piles that can be orientated to accommodate high horizontal forces and moments in addition to vertical loads. 08/08/07 Rev 2
Stratford International Station, London UK Stratford International Station, London UK Technical data Cementation Skanska Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD 9SW United Kingdom Tel: +44 (0)192 42100 Fax: +44 (0)192 42681 cementation@skanska.co.uk www.skanska.co.uk Area Offices Northern Ireland +44 (0)28 9024 2746 South West, Midlands & Wales +44 (0)1454 45200 North +44 (0)102 820888 Republic of Ireland +5 (0)1296 0790 Scotland +44 (0)141 5 22 design and manufacture of pre-stressed steel/rubber composite joints, which could readily be inserted into the diaphragm wall panel during construction. Other challenges included adapting diaphragm walling techniques to construct 0m deep panels in 12.5m headroom below high-voltage power supply cables, and for working next to live railways. Cementation Skanska also installed 100No. 1.5m diameter, low cut-off, plungecolumn, base-grouted, bored piles - drilled under bentonite, using an innovative adaptation of its patented 'Cemloc' system for accurate positioning of plunge columns for top-down construction techniques. Safety and the management of safety is a major ingredient for a successful project; Cementation worked alongside Main Contractor Skanska and Engineer RLE in improving site behaviour and safety awareness. Cementation achieved over 250,000 man hours without a reportable accident on site. At the same time, a rigorous Self- Certification system was employed to manage quality issues. Construction of the diaphragm wall commenced in July 2001, at the two ends of the station box. These were completed first to provide the launch chambers for the tunnelling machines for the two adjacent contracts. The diaphragm wall was completed in October 2002 and the finished station will follow in 2004. Technical data Client Union Rail (North) Main Contractor Skanska Construction UK Engineer Rail Link Engineering (RLE) Stratford International Station will become the major international station interchange in the east of London. Trains arriving there from continental Europe will eventually be able to choose between the London terminus at St Pancras or a direct onward journey to the Midlands, the North and Scotland. The massive international station is also seen as the trigger for a huge regeneration of this semi-derelict industrial wasteland. Owners Union Rail awarded the contract to build the gigantic, 1075m long and 24m deep, underground station to Skanska Construction with partners Cementation Skanska - the engineering design being provided by Rail Link Engineering. The construction package was let under the new Engineering Construction Contract (ECC) - with the project a model for the partnering approach to construction. At 0million, the foundations package is the largest yet awarded in the UK, and as such represented one of the more demanding challenges taken on by UK foundations and ground engineering specialist Cementation Skanska. Cementation was able not only to mobilise its Rickmansworth Head Office expertise, but also its long-established and widely experienced manufacturing and plant base in Doncaster, Yorkshire. The main element of the package was a 2 65,000m in situ reinforced concrete 15/09/08 Rev 2 15/09/08 Rev 2 4
Stratford International Station, London UK Stratford International Station, London UK diaphragm wall - forming the retaining walls for the underground box housing the new Station - which was excavated up to 24m below ground level. The diaphragm wall was between 25m and 1m deep, 1.2m and 1.5m thick, and was constructed as a series of panels 2.8m to 7.5m in plan length, to form a continuous water-tight structural wall. The panels were carefully aligned to avoid steps or 'joggles' in the wall using steel 'stop-end' formers - which were designed to facilitate the positioning of a full depth (ie. 25m to 1m) rubber water-bar at each construction joint. Ground conditions at Stratford were variable - the sequence could be simplified as essentially soft clays and silts overlying the very dense abrasive Thanet Sands. In diaphragm walling terms these are two very different soils requiring very different digging techniques. For the softer upper strata, Cementation opted for the use of rope-suspended and hydraulic grabs mounted on modern hydraulic Liebherr base units. Grabbing, as the name implies, removed the ground in large 1.5m bites of the grab jaws and deposited the spoil in the attendant dump truck for removal to the onsite Land Raise operations. Bentonite mud (a suspension of sodium montmorillonite in water) was supplied to the trench to replace the excavated material and provided support to the side walls of the excavation. Thanet Sands are altogether different; difficult to penetrate by grab, Cementation opted to mobilise No. reverse-circulation hydraulic Bauer hydromills which milled their way through the ground, using two powerful revolving wheels bristling with tungsten carbide cutting teeth. The excavated material was 'thrown' into suspension in the bentonite mud, pumped to the surface and into a 50m per hour Bauer de-sanding/ de-silting bentonite cleaning unit - which removed the silt and sand, and supplied 'clean mud' back to the excavation. Logistics planning in moving machines around efficiently - using both digging techniques for each and every panel - became an essential ingredient to the successful delivery of the project. The 12,500 tonnes of reinforcing steel was being supplied by Express Reinforcements; cages for the diaphragm wall were fabricated on horizontal 'beds' adjacent to the line of the wall. At steel densities of up to 200kg/m, individual cage weights were as high as 50 tonnes. Lifting these cages from the horizontal to the vertical, to allow the cage to be lowered carefully into the excavated panel trench, required 2 No. 15/165 tonne crawler cranes lifting in tandem - under the command of an experienced Crane Coordinator. With a predominance of 50mm reinforcing bars, lead-in order times are critical. Ancon CCL Bartec couplers were used extensively to connect the main reinforcement. This avoided what would have been unacceptable steel densities at lap positions. With such high steel densities, concrete flow through the reinforcement during casting of the diaphragm wall could have been a cause for concern. A selfcompacting high slump 40MN/m strength 2 diaphragm walling concrete was therefore specified by Cementation, with a 600mm- 700mm flow table range. Readymix Concrete expert Tarmac Topmix supplied the 85,000m of CIIIB (p/hsb - slag replacement) concrete with a minimum cementitious content of 80kg/m, from 2 No. 'wet-batch' pan mixers. The main supply was a site-based 110m /hour, 2.5m batch Elba unit, with back up from the existing plant at Bow. All loads were slumped at the panel, prior to placing, to meet Quality Control requirements. Innovation is a leading driver in the Cementation philosophy; the design of the station box called for 20 No. water-tight movement joints - providing for movement in all three planes, over a target design life of 120 years. Cementation delivered the
Slurry Trench Cut-off Walls Technical Data Application Slurry trench cut-off walls are used to control and contain leachates, gases and ground water. Normally formed using large tracked hydraulic backacter machines for depths up to 15 metres. For depths in excess of 15 metres crane based rope operated grabs can be used. Advantages Allows economic encapsulation of contaminants. No need to remove or treat contaminated soils once capped off. Slurry Trench Cut-off Walls provide barriers to the movement of gas and/or leachates from contaminated sites and refuse dumps etc. They can also be used to control the movement of ground water, where required. Where they are used to contain contaminants or refuse leachates, they are normally taken down to an impermeable stratum or at least 1 metre below the greatest depth of fill. Cut-off walls are typically 600mm thick and the target permeability of the slurry is less than 1x10-9 m/s. However, due to inherent variability in mixes and testing, at least 80% of results should be less than 1x10-9 m/s and not more than 5% of results should exceed 1x10-8 m/s at 90 days. The minimum unconfined compressive strength at 28 days age should be 50kPa. (All in accordance with the ICE Specification for Slurry Trench Cut-off Walls). Where a greater resistance to leachates or the movement of gas is required, a High Density Polyethylene (HDPE) geomembrane with a proprietary jointing system can be incorporated into the cut-off wall. Slurry walls are normally excavated using either large tracked hydraulic backacter machines for depths up to 15m, or crane based rope operated grabs for depths in excess of 15m, dependent upon ground conditions. The trench is excavated on a continuous basis under a self setting slurry with a day joint left at the end of each shift. Excavated spoil should be deposited directly into trucks for immediate removal from the working area in order to maintain a clean site and minimise the risk of excessive loading adjacent to the wall which might precipitate localised collapses. The slurry mixing station comprises bulk powder storage silos for the component materials, mixers, wet storage silos, tanks and pumps. The bentonite powder is mixed with 11/07/08 Rev 1
Slurry Trench Cut-off Walls Further information Cementation Skanska Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD 9SW United Kingdom Tel: +44 (0)192 42100 Fax: +44 (0)192 42681 cementation@skanska.co.uk www.skanska.co.uk Offices Head Office +44 (0)192 42100 North +44 (0)102 821100 South West, Midlands & Wales +44 (0)1454 45200 Scotland +44 (0)1698 75899 Northern Ireland +44 (0)28 9024 2746 Republic of Ireland +5 (0)1296 0790 water and pumped to storage silos where it is allowed to fully hydrate. GGBFS and OPC are then blended with the bentonite slurry before being pumped to the trench. Where an HDPE membrane is required it is delivered to site in sheets of a suitable width and length complete with the interlocking joints welded to the membrane. These sheets are fixed to frames and lowered into the trench, through the slurry. The frames are released and detached from the membrane when a suitable length has been installed. It is not necessary to accurately locate the membrane along the centre of the cut-off wall. Samples of the slurry are taken from the supply to the trench for strength and permeability testing at regular intervals. On completion it is normal practice to place a capping layer of clay or concrete over the top of the cut-off wall to prevent drying or shrinkage cracking of the surface. 11/07/08 Rev 1
Bored Pile Retaining Walls Technical Data Application Mainly employed in the construction of basement retaining walls, underpasses, underground tanks and structures. Choice of system depends on a variety of factors including soil type retained height, deflections, propping geometry, etc. Advantages Avoids excessive bulk excavation. Can be installed in restricted working space. When combined with Cementation guide wall/capping beam can show savings in cost and time. Can help to control ground movement. Bored cast-in-situ piles of either small or large diameter are frequently used as an efficient and economic method of constructing temporary or permanent retaining walls. These techniques are suitable for the provision of deep basements, underground structures and motorway cuttings where working space is limited or adjacent existing structures require restraint. They avoid excessive bulk excavation and help to control ground movements. There are three distinct bored pile wall options in current use: Contiguous wall Secant wall hard/soft or hard/firm Secant wall hard/hard The choice of a particular system is influenced by a number of factors. These include soil type (granular or cohesive, soft or stiff), the ground water profile (perched, high level), maximum retained heights, construction time available, propping requirements, cost and life span. Each option can be constructed using either continuous flight auger (CFA) or rotary piling methods. Pile diameters can be constructed up to 1200mm for CFA and 000mm for rotary methods. All options can be used with our combined guide wall/capping beam system. Contiguous Wall Piles are installed at centres generally 150mm greater than their diameter therefore leaving gaps in the structural wall where soil is exposed during excavation. This option is suitable where the retained soil is usually firm to stiff (not generally granular) and where the ground water table is below the level of the maximum excavation. This is the most economic option and normally the fastest method to construct. 08/07/08 Rev 1
Bored Pile Retaining Walls Further information Secant Wall hard/soft or hard/firm Secant Wall hard/hard Cementation Skanska Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD 9SW United Kingdom Tel: +44 (0)192 42100 Fax: +44 (0)192 42681 cementation@skanska.co.uk www.skanska.co.uk Offices Head Office +44 (0)192 42100 North +44 (0)102 821100 South West, Midlands & Wales +44 (0)1454 45200 Scotland +44 (0)1698 75899 Northern Ireland +44 (0)28 9024 2746 Republic of Ireland +5 (0)1296 0790 Similar to the contiguous bored pile wall but the gap between piles is filled with an unreinforced cement/bentonite mix (1 to 2N/mm 2 ) for the hard/soft wall and weak concrete (in the order of 10N/mm 2 ) for the hard/firm wall. Construction is carried out by installing the primary piles (A) and then the secondary piles (B) are formed in reinforced concrete, cutting into the primary piles. By using this form of construction the ingress of water to any subsequent excavation can be substantially reduced. This form of construction is generally used with the continuous flight auger process. Diameters can range from 500mm to 1200mm. Maximum depth of pile would be 29 metres with a recommended exposed height of 7 metres. Hard/hard wall construction procedure is very similar to a hard/firm wall but in this case the primary piles (A) are constructed in high strength concrete and may be reinforced. The Secondary piles (B) are cut into the concrete primary piles (A) using heavy duty piling rigs fitted with specially designed cutting heads. As structural concrete is used throughout there is no need to provide a lining wall. The end product provides a fully concreted face and can be an effective alternative to diaphragm wall construction. Diameters generally range from 600mm to 1200mm with a recommended depth of exposed height of 5 metres for cantilevered walls and 10 metres for a propped wall. Design Cementation Skanska's in-house design department has many years experience in bored pile and diaphragm wall construction enabling them to produce practical and economical designs with viable alternative solutions. 08/07/08 Rev 1
Cementation Skanska Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD 9SW Tel: 0192 42100 www.skanska.co.uk