Piling Productivities

 

Bored Piles

CFA Bored Piles

Driven H Piles

Advantages

Bored pile are used to support multi-story building or bridges which can producing heavy vertical loads

They are quick to install and have

no requirement for temporary or permanent casings

Driven piles are driven to a set in variable site conditions to achieve uniform minimum capacity with high reliability

Methodology

Pile drilled / soil removed and replaced with reinforced concrete

Auger drilled into ground and replaced with concrete as the auger is removed

Steel section driven into the ground

Design

Effect on adjacent ground

No displacement of the soil but the potential for relaxation / softening adjacent ground, dependant upon the soil and bore support used

Typically no displacement with good construction controls

Localised densification of loose non-cohesive soils.

Small cross sectional area and hence minimal soil displacement or potential improvement

Typical size ranges

450-2500mm diameter

450 – 1200 mm diameter depths up to 32m

150 – 350 UC’s, UBPs

Capacity

– Shaft friction

Medium

Medium

Medium

– End bearing

Very high with enlarged base

Medium

High

– Structural

Very high structural capacity and

stiffness achievable

Cage insertion can limit tensile

and flexural capacity at depth

Driving stresses often govern the steel section required

Durability

Conventional concrete in the ground design

Permanent liner in highly aggressive conditions

Conventional concrete in the ground design

Sacrificial thickness of steel above

low groundwater level

 Construction

Typical / Plant

Hydraulic or crane mounted piling rig, handling crane, casing, vibro with powerpack and / or drilling support fluid plant

Hydraulic piling rig, concrete pump and possible handling crane

Crane, vibro hammer or hydraulic hammer with powerpack or drop hammer and leaders or guide frame

Piling productivity

16m deep – 600dia @ 2No/day in soft material including a 3m soft rock socket depth. Detailed production rates

16m deep – 600dia @ 11No/day in soft material including a 3m soft rock socket depth

16m deep – 350 UC’s @ 22No/day in soft material

Material to Plant

Concrete, reinforcement cages and method dependant material

Concrete and reinforcement cages

Steel sections

Materials storage

Casing and cage lay down area

Cage lay down area

H pile lay down area

Noise

Machine only unless driven casing

Machine only

Yes, if vibro used hammer used to obtain pile set

Vibration

No, unless driven casing used

No

Yes

Spoil

100% Nett volume

100% Nett volume

None

Other

Plunged columns can be placed into the top of the pile to structural positional tolerances

Fast installation process with real time monitoring systems for construction control and records

Full strength welded splice used at connections

Predrilling can be used to overcome obstructions

Driven Tubes Piles

Precast Concrete Piles

Vibro replacement

Advantages

They are ideally suited for marine and other near shore applications with a very high end bearing capability

Precast driven piles can be environmentally friendly when construct temporary trestles in wetland

Stone piles are a very effective technique, for resolving issues with liquefiable soils, that fall within the typical grain size range

Methodology

Tube driven using external or internal hammer and filled with reinforced concrete

Pre cast section driven into the ground

Soil displaced or removed and replaced with stone

Design

Effect on adjacent ground

Large displacement of plugged tubes resulting in densification of non-cohesive soils and enhanced capacity

Large displacement resulting in densification of non-cohesive soils and enhanced capacity

Large displacement with densification of non-cohesive soils surrounding the stone column which enhances the capacity

Typical size ranges

350 – 750 mm diameter

250 – 600 mm square

600 – 1200 mm diameter

Capacity

– Shaft friction

Medium

Medium

Low

– End bearing

Very high

Very High

Low

– Structural

Tubes can be reinforced concrete filled to enhance capacity

Lifting, driving and jointing can limit capacity

Stone quality & confinement in the soil limit the capacity

Durability

Sacrificial thickness of steel and

internal reinforced concrete

Conventional concrete in the ground design Review potential corrosion at joints

Weathering / degradation of stone typically not an issue

Construction

Typical / Plant

Crane, vibro hammer or hydraulic hammer with powerpack or drop hammer, leaders

or guide frame

Crane, hydraulic hammer with powerpack or drop hammer, leaders or guide frame

Crane, vibro probe with power pack,

water pumps, compressor and front loader

Piling productivity

16m deep – 600mm Dia piles @ 22No/day

16m deep – 300mm square piles @ 20No/day

12m deep @ 6No/day in soft material

Material to Plant

Steel tubes, reinforcement cages and concrete

Precast concrete piles unless manufactured on site

Stone

Materials storage

Tube and cage lay down area

Precast pile lay down / curing area

Stone stockpiles

Noise

Yes if top driven but limited if bottom driven

Yes

Machine only

Vibration

Yes

Yes

Yes

Spoil

None, but ground heave possible

None, but ground heave possible

20 – 100% Nett volume

Other

Predrilling can be used to overcome obstructions Enlarged bases can be formed to enhance capacity

Variable pile founding depth can lead to high wastage levels and jointing expensive

Top feed “Wet” process requires water circulation system and settlement ponds to contain silts

 

 

 

Sheet Pile Wall

Secant Pile Wallblank

Diaphragm Wallblank

Advantages

Sheet piles are best suited for the following applications temporary retaining walls, cofferdams and other temporary structures

This is a permanent solution which provides increased wall stiffness compared to sheet piles  

Diaphragm walls tend to be used for retaining very deep excavations as they can be designed to take very high structural loads

Methodology

Clutched sheet piles driven into position.

A series of piles installed so that they overlap to form a wall.

A series of interlocking reinforced concrete panels.

Construction

Establishment

Cranes, vibros and hammers and / or pile jacking plant

50-60T self erecting hydraulic drilling rigs and handling crane.

50T crane + grab, handling crane,

mud conditioning plant, mud storage

Piling productivity

16m deep – 600mm wide sheet piles @ 22No/day (in clay or sand materials) Detailed production rates

16m deep – 600dia @ 4No/day in soft material including a 3m soft rock socket depth. Detailed production rates

16m deep by 800mm wide @ 14-40m3/day of completed wall per rig  per day

Materials to site

Sheet Piles

Concrete, reinforcement cages

Bentonite, reinforcement cages or concrete panels

Work face access

Plant & Materials delivery

Plant & Materials delivery

Plant materials and pipelines for mud circulation

Noise

Yes, unless jacked in

Machine only

Machine only

Vibration

Yes, unless jacked in

No

No

Spoil

No

100% nett volume

100% nett volume

Product

Wall Movement

Flexible, can be increased with clutched

king piles. More props or anchors can be

used to reduce movements

In-situ wall with ground supported

throughout construction. Very stiff.

Ground supported throughout excavation. Stiffest option given wall thickness

Watertightness

Good with joint treatment

Groundwater control over pile length and satisfactory performance with some seepages

Excellent over full depth of the wall with

waterbar across panel joints.

Connections

Welded below capping beam level

Drilled & grouted bars into piles,

shear & bending capacity possible

Full moment & shear connection via box-out and pull-out bars

Durability

Internal painting and sacrificial

thickness of steel

Conventional concrete in the ground design. Internal lining for long-term seepage

Conventional concrete in the ground design. No internal lining necessary

Load Capacity

Low end bearing capacity

Capacity can be enhanced by increasing the length of some piles

Wall has a large bearing area and individual

panels can be extended

 

 

 

 

Soldier Pile Wallblank

Bored Pile Wallblank

Soilmix/Slurry Wallblank

Advantages

Soldier pile and lagging walls are the most inexpensive systems compared to other retaining walls. They are also very easy and fast to construct

Low cost and speed of construction for temporary and permanent retaining walls and soil support 

Excellent resistance to contaminated groundwater. They have abilityto adapt to ground movements such as earthquakes

Methodology

Constructed using piles timber infill panels

(timber, steel or concrete)

Series of bored piles installed relatively close together with shotcrete arches

Steel or precast concrete elements placed in fluid soilmix / slurry

Construction

Establishment

50-60T self erecting hydraulic drilling rigs and handling crane

50-60T self erecting hydraulic drilling rigs, handling crane and concrete pumps

50T crane + grab / CSM, handling crane / grout plant with screw feed silos, high pressure pumps

Piling productivity

16m deep – 300mm square piles @ 18No/day

16m deep – 600dia @ 4No/day in soft material including a 3m soft rock socket depth. Detailed production rates

16m deep by 800mm wide @ 20-50m3/day of completed wall per rig  per day

Materials to site

Concrete, reinforcement cages, steel or precast concrete panels

Concrete, reinforcement cages

Cement, bentonite, steel or precast concrete panels

Work face access

Plant & Materials delivery

Plant & Materials delivery

Plant, materials and pipeline delivery of slurry

Noise

Yes, if driven sections

Machine only

Machine only

Vibration

Yes, if driven sections

No

No

Spoil

Dependant on installation method

100% nett volume

30%-80% Nett volume

Product

Wall Movement

Ground unsupported allowing relaxation prior placement of panels and backfilling Stiffness depends on structural section

and backfill compaction

Ground unsupported allowing relaxation prior to concrete

Finished product stiff

Ground supported with stiffness dependant on steel section.

Precast panels can increase stiffness.

Watertightness

Permeable with no groundwater control

below excavation. Seepages long term

Permeable until shotcrete in place with no

groundwater control below. Seepages long term

Good temporary performance due to

replacement with CB slurry but some seepages

Connections

Numerous connection options dependant on materials used

Drilled and grouted bars into piles, shear

and bending capacity possible

Welded to steel sections, shear & bending capacity possible.

Durability

Conventional concrete in the ground

design or sacrificial steel thickness given

long term seepage potential

Conventional concrete in ground design

Sacrificial thickness of steel and internal

lining wall for long-term groundwater seepage

Load Capacity

Capacity can be enhanced by increasing the length of piles.

Capacity can be enhanced by increasing the length of some piles.

Capacity limited by penetration of steel beams

 

 

Barrette Piles

Task / Description Slow   Ave   Fast    Units
 Rule of Thumb, overall rate by Mill 0.5  1.1  1.2   hrs/no
 Fabricate reinforcement cages –   4.0  –    hrs/cage
 Concreting barrette panels 40.0  50.0  55.0   m3/hr
 Trimming top of barrette panels –   2.4  –    days/no
 Concrete Testing, Coring Test 4.0  3.5  2.0   days/no
 Concrete Testing, Sonic Logging Test –   0.7  –    days/no

 

Bored Piling

Pre-Drilling – Site Investigation

  • Pre-boring will be carried out at each location to ascertain the target founding level.
  • Rotary rig drilling operations incorporate the use of a steel core that is used when a core sample is required.  Another type of boreing is called “Wash Bore” or “Percussive Bore” which simply means that a bore is flushed out and is used when no soil sample is required.  Typical rates are…   
Type of Strata Plant Used  Rate (m/hr)
Top soft deposits of site fill Percussive / Rotary 10.00
Grade V/IV rock deposits Wash Boring 3.15
  Triple Tube Sampling 0.75
Grade III/II rock deposits Rotary 0.50
  Triple Tube Sampling 0.50

 

With a standard rig, working a 12 hour shift, a typical output rate of 66 hrs/hole/rig is possible. 

  • As-Built Information. On Central Reclamation, Contract UA11/91, borehole drilling completed with the following results… 
  1. Average depth of 61.15 m, total depth of 428 m
  2. Average rock socket depth of 4.65 m
  3. The durations ranged from 4 to 8 days
  4. Average of 5.85 days, total duration of 41 days.

The Target Founding level

  • This is defined as the required socket into the bedrock, which is defined as moderately decomposed rock grade III or better with a core recovery greater than 85% (allowable bearing capacity of 5 mPa).  The continuity of the founding rock is demonstrated by continuing the pre-bored hole a maximum of 5 metres or 3 times the pile diameter, whichever is the greater.
  • The cores are logged, stored and photographed and submitted together with proposed founding levels for approval.

Setting Out

 

 Before starting excavation at the pile position the following steps are taken:

 

  • Survey and record the existing ground level at the pile position
  • Setout the pile location from the reference points and in order to monitor the position of the steel casing, control pins are usually established at two orthogonal positions, offset from the centre of the pile.

Pile Tolerances

  • In the case of out of position casings, adjustment can be made to keep the vertical alignment and plan position within the limits of no more than 75 mm off-centre on plan position and not deviating by more than 1:75 from the vertical axis.

Pile Excavation / Casings

  • The shaft of the pile is excavated within a temporary steel casing with an outside diameter of say approximately 200 – 300 mm greater than the pile diameter.  The casing is used mainly in areas of unstable ground and are driven using hydraulic casing oscillator attached to a crawler crane or a casing vibrator.
  • Shaft excavation is carried out using a single or double hammer grab supported by crawler crane.  The steel casing toe is kept in front of the excavation level until it is 0.5 metres above the pile cut-of level.  The pile shaft is often flooded with bentonite or water and excavation proceeds to the top of the CDG.
  • Excavation then proceeds by reverse circulation drilling (RCD) using large diameter drilling heads with special rock cutters and flushing by air lift.  Bentonite or water levels are always maintained above the ground water level to ensure stability of the shaft.

Calculation Of Bored Pile Construction / Excavation Time

  • Piling times can be reduced by the use of service cranes for reinforcement and concreting activities.
  • An additional extended shift would often be required for certain piles, as would RCD down-time. 
  • Forecast construction times can be derived by using output rates (hours per item)…

 Operation

Element 

Details 

Hours 

Add or Remove

Reverse Circluation Drill Plant (RCD)

incl drill bit

2 hrs

Add or Remove

RCD drill bit

(incl assembly of drill string)

5 hrs

 

RCD bell-out bit

(incl drill string & stabilisers)

5 hrs

Installation

Airlift tremmie tube

 

5 hrs

 

Reinforcement cages

(time for joining each cage)

2 hrs

Cleaning Time

Initial airlift cleaning

(after finishing excavation)

8 hrs

 

Final airlift cleaning

(after fixing steel cage)

2 hrs

Concreting

Incl extract casing

( < 70  m deep)           

12 hrs

 

 

( > 70 and < 95  m deep)

14 hrs

 

 

( > 95 and < 135 m deep)

48 hrs

Curing Time

Only required prior to removal of telescopic casings

 

72 hrs

Cycle Time

Move piling setup to next location

 

2 hrs

 

 

 

 

Shaft Excavation

Strata

Plant Used              

Rate (m/hr)

 

General Fill (upper ground levels)

Grab

3.50 m/hr

 

Sand, Minor Rubble

Grab

2.10 m/hr

 

Marine / Alluvium Deposits

Grab

2.50 m/hr

 

CDG < 150

RCD/Grab

1.50 m/hr

 

CDG > 150 < 200

RCD

1.00 m/hr

 

CDG > 200, Compacted Gravel

RCD

0.50 m/hr

 

CDT

RCD / Grab

0.50 m/hr

 

Corestones

RCD / Chisel

0.50 m/hr

 

Rock Socket – Grade IV/V

RCD

0.25 m/hr

 

Rock Socket – Grade II/III

RCD

0.125 m/hr

 

Rock Socket – (Tendering Rate)

RCD

0.10 m/hr

  • Forecast excavation or cycle times can then be derived by analysing ground conditions.  Site investigation will provide the depths / types of strata which can then be matched to production output rates (see above). 
  • Note – A pile’s diameter has negligible effect on production time and as such is ignored.

Example – For a pile founding on rock at 60 m deep…

 (a) Calculate Allowance For Plant Time / Other Elements (hrs)….
 

Element Hours

Set up RCD

5.0

Excavate Time

See Below

Remove RCD (including drill bit, string and stabilisers)

5.0

Setup / Remove Airlift Tremmie Tube

5.0

Initial Post-Excavation Airlifting

5.0

Place reinforcement (5 No cages @ 12m = 5 x 2 hrs)

10.0

Setup / Remove Airlift Tremmie Tube

5.0

Final Post-Reinforcement Airlifting

2.0

Concrete and remove casing

12.0

Move to next location

2.0

Calculate Total Construction / Plant Time

52.0 hrs

(b) Calculate Allowance For Excavation Time (hrs)…
 

Depth of Strata (m)

Type of Rock

Production Rate (m/hr)

Plant Used

Time (Hrs)

0 – 20

Sand/minor rubble

2.00

Grab

10.0

20 – 35

CDG less than 150

1.50

RCD/Grab

10.0

35 – 47

CDG more than 150

1.00

RCD

12.0

47 – 57

CDG > 200/corestones           

0.50

RCD

20.0

57 – 60

Rock socket

0.20

RCD

15.0

 (c) Calculate Total Pile Excavation Time = 67.0 hrs

 (d) Overall Pile Time       

Description

Calculation

Hours

Construction / Plant Time

(“b” above)

52.0 hrs

Excavation Time

(“d” above)

67.0 hrs

OVERALL CYCLE TIME

(“b” + “d”)

119 hrs

(With 12 hr shifts)

(“b” + “d”)

9.9 days


 

 Bored Pile Construction As-Builts

  •  General Rule of Thumb Pile Times (days)… 

Description

Rule of Thumb Pile Times (days)

Depth (m) =>

<20

<40

<70

<90

<135

Days Per Pile

4.0*

8.0

10.0

25.0

45.0

Note – due to the required plant assembly and operation times, 4 days is the minimum possible pile construction time for any situation.

Methods For Overcoming Obstructions

  • If the obstruction is shallow (ie 0 to 2.5 m below ground level) a backhoe-breaker will be used to form a suitable hole.
  • Where the obstructions are located at greater depths an oversized temporary casing is driven by the oscillator to the top of the obstruction.             
  • If the obstruction is above water level a hand operated air hammer is used, a typical rate of = 0.8 m/hr
  • If below water level a down the hole hammer or heavy chisel supported by crawler crane will be used, a typical rate of = 0.5 m/hr
  • If a concrete “plug” is required to provide a well formed shaft wall when an obstruction or excessive overbreak or fault is encountered… 
Element Hours
Remove RCD 5 hrs
Install Tremie Concrete Tube 5 hrs
Place Concrete Plug 2 hrs
Cure Concrete 36 hrs
Replace RCD and drill string 5 hrs
TOTAL TIME LOSS 53 hrs (2.2 days or 4.4 shifts)

Cleaning of Pile Base

  • The hole of the pile shaft is cleaned using an airlift until the water becomes clean or negligible particles in suspension is discharged.

Reinforcement Cages

  • Cages are constructed in suitable sections, usually in the order of 12 m long, complete with sonic tubes and coring tubes.
  • Fabrication, 12 m long cage with 6 no fixers… 
Description Duration
Fabricate 1 cage 2.5 hrs
Total cages required 5 no
Overall Fabrication Time 12.5 hours

Steel Stanchion Fabrication and Installation

  • Stanchions are usually fabricated off-site and delivered in sections.  Prior to installation the sections are welded together to form the complete stanchion.  Stanchion sizes are usually in the region of 525 mm x 525 mm. 
  • With an average length of say 28 m, the welding time would be around 5 days and are tested by an ultrasonic weld test and an MPI test.
  • After the installation of the reinforcing cage in to the shaft the stanchion will be lifted until it hangs vertical.  It is then lowered into the excavation and clamped into position.

Concreting

  • Pile concreting is carried out under water by “tremie” techniques maintaining the water or bentonite head inside the casing at or above existing ground water level.  The tremie tube (250mm) is withdrawn as concreting proceeds ensuring a minimum concrete head of 2 metres above the top of the tremie tube.

Sequence Of Piling

  • The sequence of construction of piles is chosen in such a manner that no damage can be caused to nearby piles still under construction or recently concreted (i.e. less than 3 days).
  • On a 12 metre grid, a normal layout would mean say having two non-worked on piles between each open excavation in the longitudinal direction (ie a 36 metre spacing) thus allowing room for the crane etc and a lesser spacing of every other pile being worked on (ie a 24 metre spacing).

 Pile Testing

  • The workability of concrete is tested on site by measuring the slump and temperature of concreting at the time of discharge into the pile shaft.  Laboratory tests are carried out in order to check the strength of the placed concrete.  A number of test cubes are made and tested at 7 and 28 days.
  • Coring Test – Certain piles selected by the Engineer will be cored their full depth.  The depth of cores into the base material (rock) will usually be at least 600 mm.  Cores are placed in correct order and relative position in core boxes which clearly mark the depths of cores.  The cores are usually photographed and submitted to the Engineer.  The testing of the coring will provide additional information about the quality of the concrete as well as the condition of the interface between concrete and rock.
  • Sonic Logging Test – In order to test the quality of the concrete as well as the integrity of the pile in its overall length and pile toe condition sonic core testing is used.  Sonic tubes are installed with the reinforcement cage in order to allow the lowering of the signal transmitter and signal receiver probe down the bottom of the pile.  These tubes are sealed at the bottom.
  • Vibration Tests – This test determines the pile length and shape and the overall pile concrete quality.  This is a specialist test.

Secant Pile Wall – Contigous Piling

Principles of Construction Often known as “Colcrete” piling, which is a type of trade name. Usually replaced by diaphragm walling methods.

Essentially typical bored piles, or down-the-hold bored piles, are constructed with a spacing such that each pile is virtually touching the next. These are constructed on a hit-and-miss basis.

After a suitable length of these piles are in place (often 9 piles or so) a smaller drilling rig follows on behind placing the “colcrete” piles. A small diameter shaft, often 100 mm or so, is drilled on the external face of the pile wall close to the interection between the two main piles. This excavated pile is fitted with a grout tube and backfilled with gravel. The pile is then grouted and forms a seal between the adjacent piles. This type of pile wall can be constructed with either a standard reinforcement cage or a “H” pile.

 

Info below achieved on project in Bermonsey, London – Sept 2010

1 rig, 600dia contig piles, 12-15m deep, 12No per day (average), 15No per day (max)

Rule of thumb based on Hit 1, Miss 3 = 8.5l/m day per rig.

Labour: 1 Rig driver, 1 banksman, 1 conc pump operative, 3 x steel fixers, 1 x 360 driver

Plant: 1x rig, 1x mini 360 exc, 1x 6m3 mixer, 1x pump, – 

Deliveries: 4 – 5No 6m3 wagons per rig per day (av 2m3 per pile)

Mobilisation: 1 day (Allow for 2 days)

Next trade – Excavate and blind around piles (for ring beam) – start 7 elasped days after last piles in the run are complete (4 working and 7 elasped days after piling start based on Hit 1 miss 3 method and 12No/d).  34 linear metres released for Groundworker to start.

All piles 600mm in dia. No smaller piles or grout tubes used as described in the post by technical development. The face of the basement wall will be faced with a single skin of blockwork at a later date (non critical).

Method: Hit 1, Miss 3

Ground Anchors

Multiple Bell Ground Anchors

Multiple Bell Ground Anchors Often used in London Clay.

  • Uncased, 10 m long 2.0 no/day
  • Top Cased type, 15 m long 1.0 no/day
  • Anchor Stressing 2.0 no/day

    Removable Ground Anchors

    Removable Ground Anchors Recent innovation of “removable” ground anchor system. Steel cables are doubles up and threaded over a roller at the anchor end. Once de-stressed, they can be pulled out. 1 rig can achieve…

    • Drill 30 m shaft 7.0 hrs
    • Install strands/setup anchor 6.0 hrs
    • Grout in strands 2.0 hrs
    • Stressing can be done 4 – 7 days after grouting.

     

      Usually at 3 m horizontal centres and can only be worked on with 5 – 6 m spacings. So a hit and miss method must be adopted, giving a significant programme constraint.

      Hand Dug Caissons

      Principles Of Construction 

      This type of “pile wall” is typical employed in areas where headroom or proximity to buildings restricts the use of large diameter bored pile drilling rigs, or where the wall is to be located very close to an existing structure.

      These are very time consuming and in allot of areas no-longer allowed as an acceptable safe construction method.

      Stringent air monitoring and safety isses are adhered to during the construction of the caisson.  An electric chain block and hoist structure is maintained at the pile head for access and egress of both materials and operatives.

       

      Site Investigation / Advanced works

      Advanced grouting is often carried out around the group of caissons in order to reduce water inflow into the caisson area and provide adequate safety factor against base heave failer.  Grouting of the area will also restrict ground settlement due to changes in the water table during caisson construction.

      A 75 mm diameter grout hole is drilled to 2 m belowthe specified toe of the caisson.  On completion of drilling, a 40 mm inside diameter PVC, Tube-a-Manchette (T-A-M) grout tube will be installed to the bottom of the grout hole. 

      The tube is usually perforated at 300 mm intervals with each perforation being covered by a tightly fitting rubber sleeve to act as one way valves.  The grout hole is often backfilled with gravel and then pumped with grout to the specified pressures etc..  After each stage of grouting the T-A-M will be flushed with water to allow future grouting as necessary.

      The slightly conical excavation core is carried out by hand and a formwork erected and concrete placed in the void between the excavation and the internal formwork.  Excavation down to the next level then begins.

       

      Excavation Of Caissons

      All excavation is carried out with air tools and shovels etc.  Material is loaded into a 0.2 m3 drum skip.  Hand excavation to a depth not exceeding 1 metre. 

      Fix a suitably braced 3 segmented tapered shutter, fix reinformcement and pour concrete to fill all voids between the external face of the lining and the earth face.  This operation is undertaken continously until the founding level is reached.

       

      Steel Reinforcement

      Reinformcement is placed either in prefabricated cages or directly erected in side the bores, depending on headroom and caisson access conditions.

      In some instances a steel “H” beam is installed in place of a reinforcement cage.

       

      Concreting

      Concrete is cast in place in one continuous operation using the tremmie pipe method, up to cutt-off level.  The concrete is generally not vibrated.

       

      As-Built Examples

      • Perimeter wall caissons, 800 mm diameter, excavated to a depth of 26 metres (HK Central Subway).
      • Excavation Time 18 – 24 days
      • Excavation to Concreteing Time  26 – 35 days
      • Difficult ground of sea wall or ground obstructions can easily increase theoverall construction time to 50 or 150 days.

      Secant Piling

      Principles Of Construction

      • Often known as “Benoto” piling, which is a type of trade name.  Usually replaced by diaphragm walling methods.
      • Essentially typical bored piles, or down-the hold type bored piles, are constructed with a spacing slightly smaller than the chosen diameter of the piles.  Once a suitable length of piling has been completed, the “holes” are filled with a similar bored pile which intersects and “bites” into the two previously constructed piles.
      • Usuall these piles are strengthened with a steel “H” pile, rather than the typical reinforcement cages used in standard bored piling.

       

        As-Built Examples

        • Large diameter circular secant pile cofferdam.
        • Structure consisting of 1,200 mm diameter secant piles to a depth of 20 which then stepped into 900 mm contiguous piles for a further 20 m depth.  Each pile was probed to 10 m depth in advance.  A total of 255 number piles were constructed.
        • The “cofferdam” had a 1.4 m deep concrete base slab with a concrete lining to the walls.
        • An intermediate concrete roof slab was placed to form an underground box structure.
        • Overall construction time  12 weeks (Heathrow Express).

        Pile Cutting Back

        Task / Description Slow   Ave   Fast    Units
         Concrete Pile Caps, 50-300mm deep and 0.6m dia 0.6  –   0.3   hrs/no
         Concrete Pile Caps, 300-750mm deep and 0.6m dia 1.5  –   0.4   hrs/no
         Concrete Pile Caps, > 750mm deep and 0.6m dia 1.8  –   0.8   hrs/no
         Concrete Pile Caps, 50-300mm deep and 1.1m dia 1.9  –   0.8   hrs/no
         Concrete Pile Caps, 300-750mm deep and 1.1m dia 2.5  –   1.1   hrs/no
         Concrete Pile Caps, > 750mm deep and 1.1m dia 4.2  –   2.3   hrs/no
         Concrete Pile Caps, 50-300mm deep and 2.5m dia 9.2  –   8.2   hrs/no
         Concrete Pile Caps, 300-750mm deep and 2.5m dia 10.1  –   9.5   hrs/no
         Concrete Pile Caps, > 750mm deep and 2.5m dia 11.5  –   10.2   hrs/no
         Concrete, Cutting Slabs, 5-25m deep –   15.2  –    m/hr
         Concrete, Cutting Slabs, 25-50m deep –   11.5  –    m/hr
         Concrete, Cutting Slabs, 50-75m deep –   6.7  –    m/hr
         Concrete, Cutting Holes, coring machine –   0.2  –    m3/hr
         Concrete, Cutting Back to expose couplers 0.7m slab –   2.5  –    m/day

        Sheet Piling

        Sheet Piling On reclamation, sand fill, sheet piling by crane and drop hammer, vibro hammer or diesel hammer.

        • A rate of 20 – 25 No/day to 20 to 35 m deep.
        • 1 no = 0.4 m wide on plan and 6 m long.
        • Therefore 8 – 10 m/day per rig is achievable.

         

        On more difficult areas, such as through existing ground or a sea wall for example.

        • A rate of 10 – 12 No/day to 20 m deep.
        • Therefore 4 – 6 m/day per rig is achievable.

        For more shallow sheet pile walls

        • Driven by – Pilemaster 60.0 m/day
        • Driven by – Automatic Drop Hammer 32.0 m/day

        Steel for piles is usually readily available and a two week lead in is often all that is required.

         

        Sheet Piling

        Task / Description Slow   Ave   Fast    Units
         Vibro/Drop Hammer, 10m deep Sand –   55.0  60.0   m/day
         Vibro/Drop Hammer, 35m deep Sand 3.5  32.0  38   m/day