Ground Movement.qxd - Building Products Index
Transcription
Ground Movement.qxd - Building Products Index
GROUND MOVEMENT THE CORDEK SOLUTION C E L L C O R E • C L AY M A S T E R • C E L L F O R M Introduction Ground movement and its associated problems are well known to Engineers and Contractors. It is caused by the rehydration of clay or expansive shale soils, overburden recovery resulting from deep excavations or, in certain parts of the world, permafrost heave. The amount of movement will depend on a number of factors including: ● ● ● The plasticity of the soil and the degree of dessication The extent to which vegetation and trees have been removed or planted The excavation depth Analysis of the site investigation should indicate the expected amount of movement. Valuable guidance is supplied in the NHBC document ‘Building Near Trees’ (Chapter 4.2) and the BRE. CELLCORE Cordek have developed a number of products to prevent ground movement damaging the integrity of commercial or residential buildings. CELLFORM They are fully proven on major projects throughout the UK and overseas. CLAYMASTER Cellcore The Cellcore range has been developed to minimise the effects of ground movement on the foundations of buildings and is extensively used on major projects both in the UK and overseas. ● Fully proven and tested ● Agrément and NHBC approved ● Made in a wide range of designs ● Water resistant and does not degrade ● Backed by quality engineering and production teams ● Inert and contains no CFCs or HCFCs Performance All grades of Cellcore and Cellform work on established engineering principles and performance, unlike other antiheave products, does not rely on material degradation. At the pre-determined load above the SAFE LOAD, which is known as the FAIL LOAD, the legs will buckle and collapse and allow the ground to move upwards. Each grade is designed to support a given thickness of concrete plus a live load allowance of 1.5kN/m2 with negligible creep compression during a 16 hour curing period (THE SAFE LOAD). The slab, beam or pile cap must be designed to accept the difference between its self weight and the fail load (see design examples on page 5). There are three types of Cellcore: Type CC Polypropylene sheet Type CF Heavy duty polypropylene sheet Type CC and CF are used beneath piled beams. Cellform also acts as permanent formwork. Both are supplied to the correct beam width. Type CP High density EPS Type CP usually used beneath the ground floor slabs and pile caps. Cellcore Plus On the Type CP, the thickness of the EPS top can be increased to provide better insulation. The table opposite shows the improved thermal properties. Thickness Thermal Resistance (mm) m2c/w 50 (Standard) 1.40 75 2.08 100 2.78 125 3.47 150 4.17 1 Cellcore The standard grades incorporate drainage slots to alleviate water pressure. Standard Grades of Cellcore Table 1 Concrete Depth and Load characteristics Cellcore Grade Maximum Concrete *Thickness Cellcore Type Beams Slabs - CP Safe Load kN/m2 Fail Load kN/m2 8 12 8/12 270mm 10/15 350mm CC CP 10 15 15/22 550mm CC CP 15 22 20/30 770mm CC CP 20 30 *Allows for 1.5kNm2 Live Load When concrete thickness exceeds 770mm please contact our Technical Services Department Cellcore Grades are available for concrete thicknesses up to 2 metres Standard Depths for Cellcore Table 2 Compression characteristics Cellcore Type Compression at Fail Load mm Type CC Depth mm Type CP Depth mm 100 150 55 175 225 100 200 250 125 300 350 200 The depth of Cellcore selected will depend on the predicted amount of ground movement at the Fail Load The thickness of the EPS top can be increased to improve the insulation value (Cellcore Plus). Selection of Cellcore Table 3 Ground movement and void characteristics Results of Soil Analysis Plasticity Index NHBC Category Predicted Ground Movement, or BRE/NHBC requirement Depth of Cellcore required to achieve ‘Equivalent Void’ Shrinkage Potential Void dimension (mm) Type CC Type CP 10-20 Low 50 100mm 150mm 20-40 Medium 100 175mm 225mm 40-60 High 150 250mm 300mm 200 300mm 350mm Above 60 Very High This category is applicable when potential ground movement exceeds the NHBC range 2 Sizes Standard Panel: 2.44m x 1.22m Beams: Manufactured to width in 2.44m lengths For non standard sizes, please contact our Technical Services Department On-site information Delivery All products are delivered in polythene packaging. Packaging material is kept to an absolute minimum. The packs are easily manually off loaded and handled. Storage and Handling The panels are all relatively light and should be weighted down to prevent damage from the wind. Apart from that, no special storage conditions are required as all products are unaffected by water. Note: Most damage is caused during off loading, storage and handling, so sensible precautions should be taken. Installation The procedure is straightforward but the following points are important: ● Ensure that Cellcore and Cellform are placed on a firm level surface. Concrete or sand blinding will often be required. ● Where necessary seal the joints with a formwork tape which can be obtained from Cordek. ● Do not overload with steel or surcharge with concrete. If you have any doubts please contact our Sales Support team on 01403 799601. 3 Claymaster The original compressible expanded polystyrene. Coloured pink, so that it can be readily identified, Claymaster is Agrément approved and water resistant. Claymaster is used on the inside of piled beams to reduce the effect of lateral movement. Typical PIled Ground Beam Claymaster does not compress significantly until loads exceed 20kN/m2. A load of 40kN/m2 is needed to produce 50% compression. Therefore, its use is not recommended under ground floor slabs, piled beams or pile caps. Whilst deep trenchfill is a typical type of house foundation, it is now less used because of improvements in piling techniques and health and safety considerations. Selection of Claymaster Table 4 lateral ground movement and void characteristics Shrinkage Potential Predicted lateral movement NHBC recommended void Low Zero Zero Medium 25mm 50mm High 35mm 75mm *Very High 60mm 100mm * This category is recognised by the BRE 4 Claymaster thickness for ‘equivalent void’ Sizes Standard sheet sizes are 2.4 x 1.2m with thicknesses ranging from 50 - 300mm. Cordek supplies Claymaster cut to beam depth at no additional charge. You only pay for the waste which is kept to a minimum. Design Examples Cordek’s Technical Department are always available to supply design advice to the specifier. DESIGN EXAMPLE - For a beam DESIGN EXAMPLE - For a slab Beam (500 mm deep) Light Slab (200mm thick) - Assume the soil survey showed a plasticity index of 14 - Table 3 on page 2 shows soil heave potential is low shrinkability - BRE/NHBC data recommends a clear Void of 50mm. - Assume the soil survey showed a plasticity index of 31. - Table 3 on page 2 shows the potential for ground movement is medium - BRE/NHBC data recommends a clear Void of 100mm. 1. Total deadweight/downward load is Self weight of 500mm concrete beam: 0.5m x 24kN/m3 = + Live load allowance = TOTAL LOAD = 12.0kN/m2 1.5kN/m2 13.5kN/m2 2. Table 1 on page 2 shows the next SAFE LOAD value is 15kN/m2 (Fail Load of 22kN/m2 ) The appropriate Cellcore grade = 15/22 3. 100mm of ground movement is predicted and Table 3 on page 2 shows that, The Cellcore depth to accommodate this = 175mm So, the full product specification = Cellcore 175 CC 15/22 Table 1 on page 2 shows this Cellcore specification has a FAIL LOAD of 22kN/m2 The beam must therefore accommodate a Residual Upward Force derived as follows: Cellcore Fail Load - Self weight of beam = 22.0 - 12.0 = Residual Upward Force 10kN/m2 Typically two modes of failure should be considered at this point. i) Lifting the beams off the top of the piles ii) Failure of the beam in bending or shear due to the uplift forces Note: Table 4 on page 4 shows the recommended void for lateral movement in medium shrinkability soils is 25mm and that a 50mm thick Claymaster grade would be required to accommodate the lateral movement if the design incorporates any perimeter downstand beams. 1. Total deadweight/downward load is:Self weight of 200mm concrete slab: 0.20m x 24kN/m3 = 4.8kN/m2 + Live load allowance = 1.5kN/m2 + No blinding screed required TOTAL LOAD = 6.3kN/m2 2. Table 1 on page 2 shows the next SAFE LOAD value is 8kN/m2 (Fail Load of 12kN/m2 ) The appropriate Cellcore grade = 8/12 3. A maximum 50mm of ground movement is predicted and Table 3 on page 2 shows that, The Cellcore depth to accommodate this in CP form = 150mm So, the product specification = Cellcore 150 CP 8/12 Table 1 on page 2 shows this Cellcore specification has a FAIL LOAD of 12kN/m2 The slab must therefore accommodate a Residual Upward Force, derived as follows: Cellcore Fail Load - Self weight of slab = Residual Upward Force 12.0 - 4.8 = 7.2kN/m2 Typically two modes of failure should be considered at this point. i) Lifting the slab off the foundations ii) Failure of the slab in bending or shear due to the uplift forces Note : The table 4 on page 4 shows that no void is required for lateral movement in low shrinkability soils, so there is no Claymaster application for this design. 5 For our detailed literature on these other Cordek Solutions, please call our technical sales on: 01403 799601 Formwork Solutions For a range of construction applications Trough & Waffle Moulds For forming ribbed concrete floors Piling Accessories A range of product solutions and systems Corform For constructing Bridge Decks Groundform A formwork system for in-situ ground beams and pile caps Correx® & Seekure For temporary protection Tipform A system for constructing steep sided landfill sites Filcor EPS For voidforming, fill and a range of other applications Creative Solutions For a range of design led applications Gas Protection If the contents of this brochure do not point to a solution for a particular application, we urge contractors and specifiers to call our Technical Sales line on 01403 799601. Our reputation is built on innovation and we have a wealth of problem solving experience for you to call on. For venting hazardous gases from under buildings Cordek Limited Spring Copse Business Park Slinfold West Sussex RH13 0SZ England Telephone 01403 799600 Facsimile 01403 791718 e-mail [email protected] w w w. c o rd e k . c o m The contents of this brochure are the copyright of Cordek Limited May 2010 and may not be reproduced without permission.
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