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HOW TO DO OF SHEET PILE WORK FOR DEEP PIT
Sheet piling is an earth retention and excavation support technique that retains soil, using steel sheet pile sections with interlocking edges. Sheet piles are installed in sequence to design depth along the planned excavation perimeter.
PERIMETER PLAN and SECTION ( SKETCH )
DESIGN
The design calculations shall make all necessary verifications as to the stability of the soil and water retention system to be constructed. De-watering system, excavation and basement construction activities are to be taken into consideration by design stages and executed by proper methods.
All relevant information such as loading data, design and construction drawings, soil and water data and excavation limits and stages shall be considered in the design of the sheet pile system.
MATERIAL DESCRIPTION (SHEET – PILE)
If It is not allows market circumstance, The material specification can be changed more than bigger size. ( in KSA are using 600mm wide of sheet pile such as SP-IIIW )
SPLICES
Subject to recommendations on maximum length for driving, steel sheet piling is generally available in lengths up to 10m~30m. Where it is necessary to increase the pile length during driving, splices can be used as see drawing.
STORING PROCEDURE OF SHEET PILES
In general, sheet piles should be stored on level ground with wooden supports. Blocking should be spaced at short intervals to prevent excessive sag in the lifts, and the sheeting should not be stacked over 2m height, and every layer shall be less than 5 sheets supported by wooden bars, which can ensure 10cm distance from the ground.
Overhang at the ends should be less than 0.6m except where vibratory hammers are used to pick the sheets up, in which case the overhang should be 1~1.2m. Lifts stored on site should not exceed the weight as shipped. When lifting, slings should be positioned so there is no concentration of weight at any point.
When lifting single pieces of sheet piling from one end only, care should be taken not to bend the sheet and cause a permanent set.
Please read also: PROCEDURE FOR WALL PRECAST CONCRETE OF MANHOLE -CIVIL
CONSTRUCTION SEQUENCE OF SHEET PILE AND DEEP PIT WORKS
Process of works
• Site Preparation – Ground Leveling
• Survey Work – Demarcation
• About Sheet Pile
• Sheet Pile installation and offsets
• Guide beam installation if required
• Sheet Pile installation – Placing and driving
• Cutting off and splicing
• Inspection of driven pile
• Sheet Pile connection (corner with L-Section)
Site Preparation
Before sheet piling work, designated work area shall be prepared for transferring of relevant equipment and tools. The area needs to be leveled and free from obstacles in the way of piling equipment.
Survey works
At the beginning of work, surveyor demarcates plot area for sheet pile line. On the demarcation line, reference line will be fixed with the rope connected to steel pins. After first sheet pile point defined, other pile locations are marked as required.
About Sheet Pile
Sheet pile is act as a temporary supportive wall that been driven to support the soft soils collapse from higher ground to lower ground. Sheet pile is usually used to support lateral load and act as a supporting wall. Sheet piles installation is recommended to support the soft soils collapse and carry out concrete works of Deep Sump pits whose depth is in the range of 5.5m – 9.0m.
Procedure for driven of sheet piles with vibratory method
While it is recognized that, in common with most civil engineering projects, a measure of flexibility is desirable to meet site conditions, every precaution must be taken to maintain the necessary standards of safety while giving the required alignment and verticality of the installed piles.
The first sheet pile must be installed with great care and attention to ensure it is vertical in both planes of the space.
It is essential that the following piles are interlocked sufficiently to the preceding pile before being released and the hammer applied. This can be achieved by a preliminary dugout trench in the wall line, which automatically reduces the driving length.
Sheet Pile Installation and offsets
Outer sheet piles are installed ( with 5m offset from the deep pit structure) first on the three sides to the required elevation as required based on the IFC drawing and Geotechnical investigation report, and one side is left open for moving manpower, equipment for earthwork excavation and for removal of excavated material to designated area to dumping yard. Fourth side sheet piling with 10m opening is done as and when required.
Leaving 3 m offset from the outer sheet piles, inner sheet piles are installed to the required elevation as shown in the IFC drawing based on Geotechnical investigation report, covering three sides and leaving fourth side open for moving manpower, equipment for earthwork excavation, backfilling, scaffolding material, rebar for rebar installation, formwork material for formwork installation, concrete works and removal of excavated material from the site.
Fourth side sheet piling with required opening is done as and when required. Sheet Piling Driving process involves the following steps:
The following Construction Method Statement (CMS) describes the construction procedures, the materials and equipment required for the installation of sheet pile at seawater intake pump station area.
Guide Beam Installation
For leaner installation of sheet pile, guide beam need to be set parallel on the ground along the planned sheet pile driving line. The roll of guide beam is prevention of sheet pile movement, when pile driving work is ongoing. Before pile driving, required beam length or adaptability of installation shall be determined according to soil condition.
Pile Driving Equipment
Before starting driving sheet pile, equipment such as Vibro hammer and power pack are used to drive the sheet piles as per the procedure.
Sheet Pile Installation
After preparing all the sheet pile driving equipment, sheet piles can be started to place on the location that shown in the construction drawings. Guide structures needs to be carried on to ensure the sheet pilings are placed and driven to the correct alignment.
After the sheet piles are set on place, Vibro hammer and power pack equipment will be used to drive the sheet piles. Sheet piles have to be driven to the required elevation with the proper size of hammer and by approved methods to ensure no damage to the sheet piles and proper interlocking throughout their lengths. A protecting cap shall be employed on the
tops of sheet pile to prevent damage during driving with hammer.
Apply vibration while driving sheet piles into soil reduces friction between soil and pile. During the driving progress, the granular soil immediately adjacent to the pile is effectively fluidized, and friction is considerably reduced.
Cutting-Off and Splicing
After driving the sheet piles into the ground, if found that they need additional penetration, splicing or jointing works will be carried on. Driving works will be done again for the sheet piles until it reaches its’ limit on the ground. After this, excessive of sheet pile will be cuttingoff and removed from the site ( if necessary ). All cutting-off work must be done with good
workmanship keeping safety in consideration.
Inspection of Driven Piling
Inspect the interlocked joints of driven sheet piles extending above ground. If found that the sheet piles are out of interlock, then the sheet piles have to be removed and replaced with a new sheet pile.
Sheet Pile Connection (Corner Section, L-shape Plate as per IFC drawing )
After the completion of sheet pile driving, to secure more stability of sheet piles, L-shape steel plate with necessary thickness shall be welded on corner section between existing sheet pile and newly installed permanent sheet pile with details as shown in the IFC drawing sheet piles are extracted after the completion of Deep pit works.
EXECUTION PROCEDURE OF DEEP SUMP PIT CONCRETE WORKS
After the installation of sheet piles to the toe level, Deep sump pit related works to commence. Surveyor performs setting out and marking activities to start earthwork excavation works providing 2m working space between the inner sheet pile layer and deep sump pit After the completion of Deep pit concrete works and backfill works, sheet piles are extracted.
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