The installation of sheet piles are the famous type of temporary works for the construction of building or bridge during foundation works such as pilecap structural. Steel sheet piles are long structural sections with a vertical interlocking system that creates a continuous wall.
The walls are most often used to retain either soil or water. The ability of a sheet pile section to perform is dependent upon its geometry and the soils it is driven into. The pile transfers pressure from the high side of the wall to the soil in front of the wall.
There are permanent and temporary applications. Permanent sheet piles remain in the ground and serve as permanent retaining structures. Temporary sheet piles are designed to provide safe access for construction, and are then removed.
However in the construction works today with amount of contract sum too low due to the tight competition during tender process and in order to secure profit margin sometime we overseen and under estimate the ground condition without take considered the temporary cost such as sheet piles.
If the contract awarded based on the bill of quantities it so lucky if the client could agree on the variation order for the additional works. Sometimes it so hard to fight because in the normal contract document all the temporary work such as providing access and etc within period of construction have included under general works and preliminaries item.
Much worse if the contract is based on lump sum amount where all risk shall be under contractor obligation.
Sheet pile design must account for earth, water, and adjacent structures. Sheet pile design can be straightforward in simple cases, and quite complex in some other conditions.
Many unknowns and factors that influence the behaviour of the sheet pile wall. Typically, there are two systems in sheet pile wall that must be designed:
A) Cantilever Sheet Piles - the sheet pile wall that retains the earth and water ( etc.),
Design of cantilever sheet pile wall includes two parts:
- Design the embed length of sheet pile against rotational failure.
- Select the sheet pile section to resist moment and shear:
B) Achored Sheet Piles - the Support System (i.e. the internal or external bracing such as rakers, struts, or tiebacks) that supports the sheet pile wall.
Commonly assumed failure mode of cantilever and anchored sheet piles are shown below:
Based of my experience it so easy for construction team if any ground condition have been taken measure during design stage so that it can determine either the temporary sheet pile to be considered in the bills of quantities in order to avert any delay of the construction works.
The temporary works using sheet piles shall be deemed proper design if the ground structural located in swamp area. Never under estimate with the length of sheet piles shall providing for those area because it can cause more problem and cost as followings:
The example method statement for the installation of sheet piles during Double Track Project Rawang - Ipoh as one of my favourite project site as site engineer as followings
1.0 METHOD STATEMENT OF INSTALLATION OF SHEET PILES
This method statement describes the method and procedures involved in the installation of sheet pile wall (refer to attached drawings) as temporary shoring and facilitate the work relating to the construction of the proposed railway bridge.
The technical specification and other relevant information on machinery and equipment used in this works are included.
2.1 Sheet piles
The sheet pile is a U Section and will be installed by means of a Vibro Hammer. As the pile comes in 12m or shorter lengths, welding will be used to join the sheet piles if a longer length is required. On the other hand, Oxy-acetylene will be used to cut the sheet piles if these protrude out and causes a danger to the trains passage. The sheet piles used will be the type of FSP Type III (British Standard).
2.2 I- Beams
Two I-Beams, will be used as a temporary guide for initial start of sheet pile installation.
3.0 EQUIPMENT AND RESOURCES
a) Truck crane (minimum 20 M ton)
b) 3 – 7 tons Hydraulic vibro-hammer c/w power pack (depending on site conditions)
c) Welding set
d) Back Hoe (if required)
4.1 Work Access
These preparation works proceed both piling and staging activities.
1. The site shall be levelled to allow safe operation of heavy machinery.
2. Steel plates will be provided at locations where the ground is soft and unable to support the machinery.
3. Fabrication and stocking of material such as sheet piles and other work related material will be within the bridge ROW. Exact location will be subject to site constraints.
4. Gas palettes and welding machines will located close to the place of work.
4.2 Work Flow
Before start installation of sheet piles, the location and grid line need to prepare to control the straightness and verticality on the position. The sheet piles will be installed between two guides of I-beam and a short temporary sheet pile location as a guide to install the sheet pile. The temporary short sheet pile to be use as initial guide, when start installation.
A vibro-hammer suspended with a crawler crane will vibrate the piles to the required depth.
The following sequence will be used during sheet pile installation: -
i) Surveyor locates centre of sheet pile wall.
ii) Appropriate reference line and offset point to the centre of piles to be set out.
iii) Arrange the piles at each point with the use of a timber frame to ease and maximise installation.
iv) Use vibro-hammer to install piles, a level may be used in checking the verticality of the sheet pile wall. Two I-Beams will be used to guide and correct the pile verticality and position.
v) Piling will continue until the desired depth is attained.
vi) Repeat step iii to vi for the next sheet pile and steps i to vi for every new sheet pile wall.
Length of Sheet Pile
i) Sheet piles will be delivered in 12m or shorter lengths.
ii) Oxy-acetylene will be used to cut the piles to maintain the designed length.
iii) Once sheet pile walls are installed, waler and ground anchor works will proceed.
iv) Construction of permanent retaining wall and bridge works shall than proceed.
v) After completion of one half of bridge works and diversion of track, dismantling of sheet pile walls will be carried out.
vi) The sheet pile wall will be dismantled in the following sequence:-
De-stressing of tendon
Removal of anchor head
Removal of Waler
Extraction of sheet piles by vibro-hammer
Stock piling and removal off site.
5.0 QUALITY CONTROL PROCEDURE
To accurate installation of sheet piles, all the measurement, level and position of sheet piles will be determined before commencement of the work. If longer sheet pile required proper welding, join will be used as specification required. Each of sheet pile installation on interval time, the verticality will be monitored. The installation will be going on until the length or set required.
6.0 HEALTH, SAFETY AND ENVIRONMENT
6.1 Working Hour
Line block will be applied during sheet piling works as the sheet pile wall will be installed very near to the track and might pose a danger to trains as well as to the track. All KTM regulations regarding line blocks will be adhered to.
All site activities shall comply strictly with KTM regulations and requirements.
Before commencement of works, all relevant staff will be briefed and trained to comply with KTM regulations.
A joint inspection of the track will be carried out with the consultants and KTM before work commenced. Existing track levels will be monitored at every 5m by checking the settlement marker using survey equipment within the bridge ROW before work start. The settlement will be monitored continuously by visual inspection and survey during works, on repair before line block removed and after 2 trains passed. If the track settles more than 18mm (refer to Table 126.96.36.199 in specification Rev B1), all work will be stopped and a track repair team will be informed to repair the track immediately. Similar checking will be carried out for lateral alignment by setting a reference line. If the alignment out by 18mm, all work will be stopped and a track repair team will be informed to repair the track immediately.
After installation of the sheet piles, the movement of the sheet piles will be monitored regularly during and after the excavation works.
All workers are to wear orange vest, safety helmet and safety shoes within KTM ROW. All safety issues will be governed by the Health and Safety plan and adhered to strictly.
6.5 Environmental issues
The Environmental Plan will be adhered to strictly on site.