GUIDE FOR DESIGNING RETAINING WALLS USING …

1 ELITE PRECAST CONCRETE LIMITED REFERENCE GUIDE FOR DESIGNING RETAINING WALLS USING INTERLOCKING CONCRETE BLOCKS Document No. EPCL-2017-RWRG-01 P01 June 2017 Tellus Design Limited SE008, e-Innovation Centre, Telford Campus, Priorslee, Telford, Shropshire, TF2 9FT, UK Tel: 01952 288331 Reference GUIDE For DESIGNING RETAINING WALLS USING Interlocking Concrete Blocks EPCL-2017-RWRG-01-P01 June 2017 1 CONTENTS 1. Introduction 2. Design method 3. Design input Ground conditions Geometrical information Actions Service requirements 4. Design calculations External stability Bearing resistance Sliding resistance Toppling resistance Overall stability Internal stability Sliding resistance Toppling resistance 5.

2 Other design considerations Drainage Flooding Temporary works Construction loading Parapets and handrails Front face batter 6. Design example 7. Conclusions Conditions and limitations This publication is intended as a general overview of the subjects dealt with and is not intended and should not be used as a substitute for taking detailed and specific advice in any specific situation. The recommendations and advice given in this document are given without liability on the part of Tellus Design Ltd, Elite Precast Concrete Ltd or its employees and should not be relied upon for any particular action or inaction. Tellus Design Ltd and Elite Precast Concrete Ltd shall not be liable to compensate any other party for any loss, including any consequential loss, arising out of any inaccuracies in or omissions from this document.

3 Reference GUIDE For DESIGNING RETAINING WALLS USING Interlocking Concrete Blocks EPCL-2017-RWRG-01-P01 June 2017 2 1. Introduction This document has been prepared to provide guidance when DESIGNING RETAINING WALLS USING Elite Precast Concrete Limited s interlocking concrete blocks. It is intended to assist civil/structural engineers and architects in the best practice of DESIGNING these types of gravity RETAINING structure . Elite Precast Concrete Ltd (EPCL) supply three interlocking concrete block systems; Vee , Duo and Legato . Each system comprises precast blocks manufactured from high strength unreinforced concrete. The blocks are dry laid and incorporate interlocking elements to distribute loads between adjacent blocks. For each block type, the standard block size is supplemented by blocks of different dimensions to facilitate various wall layouts.

4 The standard block dimensions for the three systems are shown in Figure Figure Standard block dimensions (mm) These interlocking block systems may be used for both free-standing WALLS and RETAINING WALLS . Typical free-standing wall applications include: Flood barriers Traffic calming/segregation Security barriers/fencing For free-standing wall applications, the structure may be required to resist hydrostatic loads from flood waters, vehicle impact loads and wind pressure. RETAINING wall applications are many and varied, but include the following applications for interlocking blocks: Bay WALLS /push WALLS to storage facilities for grain, salt, silage, aggregate and waste materials Earth RETAINING WALLS to support embankments/cuttings for both temporary and permanent works For RETAINING wall applications, the structure must be designed to resist the forces from the retained material acting on one side of the wall.

5 Over its intended service life, other loads may also be applied to the structure . Some of the advantages of USING large precast concrete block systems for RETAINING structures include: Relatively low cost Simple and quick to build dry laid ensures structure can be loaded without waiting for concrete/mortar to set Durable with low on-going maintenance costs Re-usable structures can be readily dismantled and reused elsewhere Different organisations may be responsible for the design, manufacture, installation and maintenance of the RETAINING wall as described below: Design Professionally qualified civil, structural or geotechnical engineer. May also require an independent third- party engineer to perform a design check, especially for road and rail infrastructure projects Manufacture Precast concrete manufacturer, such as Elite Precast Concrete Ltd Installation Civil/building contractor or specialist earthworks sub-contractor Maintenance Owner/operator of the infrastructure or storage facility 800 450 610 Vee block Duo block Legato block Reference GUIDE For DESIGNING RETAINING WALLS USING Interlocking Concrete Blocks EPCL-2017-RWRG-01-P01 June 2017 3 2.

6 Design method This guidance document is primarily concerned with the design of RETAINING WALLS rather than free-standing WALLS . However, many of the design considerations are equally applicable to be both types of structure . The design of RETAINING structures in the UK should conform with the requirements of the structural Eurocodes and associated UK National Annexes. These Eurocodes have largely replaced British Standards, although other documents exist that provide non-contradictory complimentary information for use with the Eurocodes. In addition, some major client organisations, such as Network Rail and Highways England, have their own standards that address aspects of RETAINING wall design. For this guidance document, the following standards are relevant: BS EN1990 (+ UK NA to BS EN1990) eurocode 0 Basis of structural design BS EN1991 (+ UK NA to BS EN1991) eurocode 1 - Actions on structures BS EN1997 (+ UK NA to BS EN1997) eurocode 7 Geotechnical design BS 8002:2015 Code of practice for earth RETAINING structures (non-contradictory complimentary recommendations for use in conjunction with BS EN1997-1 and its UK NA) PD 6694-1:2011 Published Document - Recommendations for the design of structures subject to traffic loading to BS EN 1997-1:2004 Section of eurocode 7 defines a RETAINING wall is as a structure which.

7 Retains ground comprising soil, rock or backfill and water. Material is retained if it is kept at a slope steeper than it would eventually adopt if no structure were present . There are many types of RETAINING structure which have been grouped into three main categories in eurocode 7: Gravity WALLS relatively wide WALLS having a base footing Embedded WALLS relatively thin WALLS relying on lateral earth resistance and their own structural resistance, such as cantilever sheet pile WALLS Composite RETAINING structures WALLS composed of both gravity and embedded wall elements, such as double sheet pile wall cofferdams WALLS formed from interlocking concrete blocks are designed as gravity WALLS , defined in BS 8002:2015 as follows: Gravity RETAINING WALLS are earth RETAINING structures that depend primarily on their own self-weight (and that of any enclosed material) to support the retained ground and any structures or loads placed upon it.

8 Section of eurocode 7 lists the minimum limit state requirements for all types of RETAINING structure including loss of overall stability, failure of a structural element, excessive movement and unacceptable leakage. In addition, the standard lists the following limit states that shall be considered for gravity WALLS (see Figure ): bearing resistance failure of the soil below the base failure by sliding at the base; failure by toppling; Figure Ultimate limit states for gravity RETAINING WALLS Toppling Sliding Bearing Reference GUIDE For DESIGNING RETAINING WALLS USING Interlocking Concrete Blocks EPCL-2017-RWRG-01-P01 June 2017 4 The retained ground (or stored materials) and imposed surcharge loads exert pressures on the retained side of the wall (see Figure ).

9 These are considered unfavourable actions as they are acting to de-stabilise the structure . The self-weight of the RETAINING wall is usually a favourable action , as the effects of it are to counter the effects of the unfavourable actions. For bearing failure, the self-weight of the wall may be favourable or unfavourable . Figure Favourable and unfavourable actions applied to gravity RETAINING wall , Methods for determining the values of retained earth pressures are included in Annex C of eurocode 7. For gravity WALLS at the ultimate limit state, it is assumed that sufficient wall movement has occurred for active conditions to be applicable. The retained earth pressure, a, is then calculated USING the active earth pressure coefficient, Ka, based upon expression in eurocode 7: a(z) = Ka [ dz + q u] + u c Kac where the integration is taken from ground surface to depth z.

10 For the wall shown in Figure and assuming zero cohesion and no pore water pressures ( u = 0kPa and c = 0kPa), the sum of the unfavourable actions acting on the retained side of the structure is therefore: Pa = [ Ka H ] + [Ka q H] From these expressions, the magnitude of the unfavourable actions depends upon the values of the retained soil density, , the retained height of the wall, H, and the vertical surcharge load, q. Increasing the value of any of these parameters will increase the de-stabilising actions. The active earth pressure coefficient, Ka, is a function of: Angle of shearing resistance of the retained material, Slope angle of the retained material behind the wall, (must be for material with zero cohesion) Interface shearing angle between the retained material and the wall, (usually taken as proportion of ) Methods for calculating the value of Ka include those by Rankine and Coulomb.