Technical Note No.6 Trench Lining Systems - Design ... - Groundforce

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Note that the allowable pressures at the maximum stated depths comfortably exceed the TBG pressure requirements. As a further guide for the selection of the best system, the tractive forces required to extract boxes can be considerable. The following table can be used as a guide for excavator sizing. Trench Box Extraction Forces Where the end wall of a trench requires support it is essential that no lateral load is applied to the box struts. Purpose made end closure panels are available for closing off the ends of boxes if required. Any contractor designed end support members must thrust off the ends of the box panels. The structural adequacy and integrity of non-standard end support members is the responsibility of the contractor. Note: Groundforce does not recommend the practice of “flying” trench boxes above the base of the excavation as this can potentially overload the lower struts. Drag Boxes Drag boxes as their name suggests are intended to be pulled or dragged through the excavation as the work proceeds. They are therefore designed to be used in pre-dominantly stable ground conditions in battered excavations. They therefore act as shields to protect the workforce rather that provide positive ground support as in the case of a trench box. Drag box plates do have a working load capacity commensurate with their height and would evidently provide support in the case of ground movement. However it is not industry policy to provide site-specific designs with this equipment type. Any assessment for the use of drag boxes should be carried out at site level where first hand knowledge of ground conditions and hence short-term ground stability is available. Rev E – 06/04/10
Chain attachment points on boxes All boxes are equipped with two types of chain attachment points. Handling points as the name suggests are provided at various locations around the box panels to enable them to be slung for assembly purposes in both horizontal and vertical planes. Lifting points are much heavier duty constructions designed to take the full weight of the box including extraction forces when pulling them out of the ground. These points are located in the top of the box panels and are denoted by red paint. Notes: 1. Lifting points can be used for handling purposes but handling points must not be used for lifting assembled boxes. 2. Chain attachment points have been designed in accordance with BS EN 13331-1: 2002. clause 7.4. 3. No separate certification is required for these points under LOLER MAP system boxes The modular aluminium panel box system is a lightweight yet high strength box system that can be assembled by hand and lifted and handled by backhoe type excavators. Using just three main components - panels, struts, and corner posts, the system provides great versatility by allowing 2, 3, and 4 sided support as the job demands. Note that MAP boxes do not fall within the scope of BS EN 13331-1:2002 MAP Panel Length Maximum Depth (m) Allowable Uniform Panel Pressure (kN/m 2 )# 990mm 4.8* 100.0 1600mm 4.8* 60.0 * Panels are 600mm high, posts are either 1200mm or 1800mm high. # assuming two struts per individual post Installation Installation and on-going inspection must be under the supervision of a competent person. User guides are available for all equipment referred to in this document. Note: A toolbox talk DVD is available for box installations. Ring 0800 000 345 for details. Rev E – 06/04/10
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Technical Note No.6 Trench Lining Systems - Design ... - Groundforce

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