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

Technical Note No.6
Trench Lining Systems - Design Statement
Trench Boxes
Groundforce Shorco supplied trench boxes have been designed (in accordance with BS EN 13331-
1: 2002) to support the worst ground conditions that can reasonably be expected to be encountered
within the dimensional capabilities of the panels, including the upper panels. It is therefore not
normally necessary to carry out site-specific soil pressure calculations. Exceptions to this
however are in high surcharge applications, the proximity of sensitive structures, deep (greater than
4m) excavations in very poor ground e.g. very soft clays and wide (greater than 3m) trenches.
In addition, all trench box systems supplied by Groundforce Shorco have been verified and
approved by the German regulatory body TBG to accommodate their block (uniform) pressure
diagram shown below. The pressure values tabulated include large safety allowances and can
therefore be used for most trench lining applications without further calculation.
TBG Allowable Soil Pressure Diagram
The following table indicates the maximum depths that Groundforce supplied boxes can be
used up to without further calculation (subject to the conditions stated earlier).
Box Type
Maximum Depth
Allowable Uniform Panel Pressure (kN/m 2 )
(m)
Backhoe (trench and
4** 20
manhole types)
Mini
Mini Multi-box
4**
4**
35.4
31.8
Standard
Standard Multi-box
5.2**
5.2**
44.2
34.1
Premier /
Magnum
6.6**
6.0**
38.1
34.1
Manhole box 5.5** 51.6 for 2.5m & 3m long panels, 44.2 for 3.5m panels,
38.7 for 4m panels), 40 for 4.7m panels
Rolling Strut 4 # 34.1 #
**Based on a lower and two upper panels
# Base box only, with strut in the highest position
Rev E – 06/04/10

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