Technical Specification of Works
for Construction of 33 nos. 15 cm diameter Micro bore piles at Harten Bridge over Kabul River in Kabul,
Afghanistan
1.1
Following all the investigations and the geotechnical tests it is clear that the right abutment has rotated
allowing the settlement of the right arch.
There is a general engineering, technical consensus that the consolidation can be done with the construction of
“micro bore” piles. This technology is 50 years old proven and it is successfully used in all similar cases as
settlements caused by loss of bearing capacity of the underground soil at certain levels.
1.2
It is well known that a micro-bore pile diam. 15 cm 20 meters deep can carry 20 tons.
The quantities of micro-bore piles are the following:
Vertical
Inclined at (
30 degrees)
Diameter in mm
4
5
250
depth
20m
16m
Right arch
5
250
Pier at the
center
15
0
150
Left arch
4
5
250
Remarks
At the river bed close to the
arch at the location of the
tilted tower No 3. To protect
it from further tilting.
20m
20m
1.3 While the central and right abutment do not present settlements or cracks It is felt necessary to build some
reinforcement for possible probable future over loads, specifically because Kabul is an high Seismic zone IV.
2.
SCOPE OF WORKS FOR THE CONSTRUCTION OF THE MICRO-BORE PILES
2.1
Traffic deviations: the operations are eminently the following:
2.1.1
The traffic using the bridge will be reduced to two lanes. In example: while working on the central lane, two
lane right and left will be kept open.
Similarly, while working on the left lane, the central and the right will be kept open at the disposal of the
traffic.
BORING
2.1.2
3.
3.1 Boring must be done by rotary rigs (NO HAMMER OR ANY PERCUSSION TOOL
ALLOWED), with diamond crown drilling bits.
3.1.1
OF ANY KIND IS
Boring should be done contemporarily on the three abutments to comply with the construction schedule.
3.1.2. The diameter of the boring shall be nominal 6 inch ( 152.4mm) and 10 inchor 25.4 mm 3 mm thickness
Typical standards EN 10219 – S235JHR, S275JOH/J2H, S 355 JOH/J2H or equivalent as approved by the engineer.
The total depth from the “Absolute Zero” of the Project is 20 meters land 16 m as indicated above.
3.1.3 The steel tubes can be provided with a mounting or dismounting thread every 1,5 meters.
4.
METHOD OF CONSTRUCTION
4.1.1
After complete boring up to a depth of 20 meters, the Contractor shall install the casing composed by a steel
pipe, as specified in above 3.1.2
4.1.2
The contractor shall provide the drilling rigs with a device to raise the steel casing every 1.5 meter.
4.1.3
The contractor shall install in the steel bars built according to the structural drawings (attached).
4.1.4
The contractor shall pump the specified concrete down to the maximum depth. This until the concrete reach
1.5 meter level.
4.1.5
The concrete shall have a mix composed by fine sand, sand and fine gravel, according to the “granulometry
” approved by the Engineer.
4.1.6 The casing will be lifted by one and half meter.
4.1.7
The top of the casing will be cut or unscrewed. The air tight top will be installed.
4.1.8
The Top will be connected to the high pressure hose of the compressed air.
4.1.9
The compressed air will injected at the pressure approved by the Engineer.
4.1.10
The quantity of concrete at the bottom will be measured and re-cast to allow for the concrete that has
expanded laterally following the compressed air injected.
5.
THE OPERATIONS WILL BE REPEATED EVERY 1.5 METER OF DEPTH.
5.1.1
The operations listed in above point 4 shall be repeated on a revolving basis all over the holes drilled, for
each “Construction Lane” closed to the traffic for construction reasons.
5.1.2
The Contractor shall ensure that the air pressure will assure an expansion of the concrete cast in the casing.
5.1.3
The concrete will be mixed with appropriate fluid improving additives as approved by the Engineer.
6.
HEAD OF THE MICRO-BORE PILES
6.1.1
The head of the micro-bore piles shall be built with special care, to be connected to a “pressure” distributing
structural entity to the approval of engineer.
6.1.2
The ”structural pressure distributing head” will be made either in reinforced concrete or by injection of
special resins in the head of the arch next to the head of the abutment. Relevant Drawings and
specifications will be delivered during the execution of the Works. These Works shall be subject to a
“Variation order”.
7.
QUALITY CONTROL
7.1.1
The Contractor shall exercise the best “Due Diligence” during all of these construction phases, to ensure an
effective transfer of loads from the actual foundations to the new micro-bore piles.
7,1.2
These works shall be subject to all ACI standards and specifications applicable to this works.