RE-WALL METHODOLOGY: OUTER RING ROAD-NAIROBI RE-WALL METHODOLOGY: OUTER RING ROAD-NAIROBI
Introduction Introduction
The reinforced earth retaining wall is
The reinforced earth retaining wall is a coherent gravity structure engineered to resista coherent gravity structure engineered to resist specific loading requirement. The primary components of this re-wall will
specific loading requirement. The primary components of this re-wall will consist ofconsist of alternating layers of backfill and high-adherence soil reinforcing tapes or
alternating layers of backfill and high-adherence soil reinforcing tapes or strips tostrips to which a modular precast concrete facing is
which a modular precast concrete facing is attached. Its strength and stability will attached. Its strength and stability will bebe derived from the frictional interaction between the
derived from the frictional interaction between the backfill and the reinforcements,backfill and the reinforcements, resulting in a permanent and predictable bond that
resulting in a permanent and predictable bond that creates a unique compositecreates a unique composite construction material. A mechanical connection between the facing
construction material. A mechanical connection between the facing panels and thepanels and the soil reinforcing strips w
soil reinforcing strips will be achieved by ill be achieved by way of a spway of a special tie strip embeecial tie strip embed. d. ThisThis connection creates a system that is technically sound and highly reliable
connection creates a system that is technically sound and highly reliable because ofbecause of the improved mechanical properties of the soil. The inherent strength and
the improved mechanical properties of the soil. The inherent strength and flexibility of flexibility of the overall wall system gives designers a powerful
the overall wall system gives designers a powerful way to economically solve difficultway to economically solve difficult stability issues for structures subect to
stability issues for structures subect to flooding or other dynamic forces, or flooding or other dynamic forces, or those inthose in seismically active areas.
seismically active areas.
!ompared with other types of retaining wall,
!ompared with other types of retaining wall, the reinforced earth retaining wall hasthe reinforced earth retaining wall has the following maor
the following maor advantages"advantages"
•
• It is advantageous over cast-in-place wall, both in It is advantageous over cast-in-place wall, both in construction time andconstruction time and
quantity of materials. It is quick to build thus saving time and cost even on the quantity of materials. It is quick to build thus saving time and cost even on the side of labour. !ompared to the normal retaining wall, reinforced earth
side of labour. !ompared to the normal retaining wall, reinforced earth retaining wall can save up to #$% of the cost.
retaining wall can save up to #$% of the cost.
•
• It is also It is also flexible, making it possible to build flexible, making it possible to build directly upon compressible soilsdirectly upon compressible soils
and therefore deep excavations need not to be done thus
and therefore deep excavations need not to be done thus reducing cost.reducing cost.
•
• The wall has high load-carrying capabilities, both to The wall has high load-carrying capabilities, both to static and dynamic loadsstatic and dynamic loads
as a result of
as a result of reinforced earth through several layers of high strength tensilereinforced earth through several layers of high strength tensile strips.
strips.
•
• &ince it uses prefabricated components, it is &ince it uses prefabricated components, it is easy to install therefore making iteasy to install therefore making it
rapid and predictable in terms of
rapid and predictable in terms of construction period.construction period.
•
• It is aesthetically appealing since the facing is It is aesthetically appealing since the facing is highly suited for architecturalhighly suited for architectural
finishes. The regular shape of the blocks and their
finishes. The regular shape of the blocks and their arrangement brings out thearrangement brings out the architectural feeling.
• !onstruction does not require any scaffolding permitting minimum
encroachment to right-of-way.
• 'equirements for detour and disruption to traffic can be considerably reduced.
This technology of reinforced earth re-wall was fi rst used in Thika superhighway and it has proved to be an effective way of retaining earth where space is paramount. This strengthens the desire of this company to use the same method on outer-ring road besides its advantages aforementioned.
Method feature
(. It)s a new technological innovation.
#. The method of construction is highly technical and will be strictly done in accordance with the construction drawings and specifications.
*. The mechani+ation of the construction process will help the process of construction to finish within the given time.
. The construction process control demands high field coordination.
. !onstruction quality requires the construction details to be followed strictly.
!co"e
This method of construction is very effective and can be applied in highway
construction, bridges, other areas affected by high water tables as well as dams. The versatility of the technology allows engineers and architects wide-ranging flexibility in terms addressing geotechnical, geometrical, and architectural
requirements.
The "roce "rinci"#e
The primary components of a 'einforced arth wall consist of alternating layers of granular backfill, and linear metallic, high-adherence soil reinforcing strips or ladders to which a modular precast concrete facing is attached. The strength and stability are derived from the frictional interaction between the granular backfill and the
reinforcements, resulting in a permanent and predictable bond that creates a unique composite construction material. In this proect, the process will use a reinforced plastic composite !AT*$$#$/ which will be designed according to the requirements in length and numbers arranged in the filling to improve the mechanical properties of the soil.
Foundation engineering and precast panel
Panel mounting
Panel checking
Laying of geobelts
Checking geobelts
Spread lling material
Check lling material
Compacting lling material materui
Top level achieved
Subsidiaries and defence, drainage works
Completion and inspection
Panel adustments
!dusting geobelts
Filling material adustment
"ore compaction and panel adustment
The "roce of o"eration
0ig" 0low chart 'einforced 'etaining 1all !onstruction (. 2reparations"
The team will acquaint itself with the design document before construction. It will perform a survey of raw materials available, sample panels as well as foundation concrete mix design according to the design documents and construction
specifications of prefabricated panels.
Check degree of compaction and
3etailed construction design will be created and leadership built through having construction and supervision departments designate people with clear
responsibilities4
#. !onstruction survey controls will be put in place which include"
• 5easurement of the centre line for the base construction
• 6ocating and measuring the centre line for the wall construction. • stablishing the level of base construction and set a standard point • !learing the area of the base and compact it to the level of the strips.
*. 0oundation construction
• The trench for panel foundation will be excavated and prepared according to
the design requirements. In case of unexpected geological condition during excavation, the reference shall be made to the design document in order to make the appropriate changes or remedies.
• 0or the wall exceeding ($m long, a settlement or expansion oint of ($mm
wide will be created and this will be consistent throughout the wall. The top surface of each segment will have the same hori+ontal plane and be in line with the panel modulus. 'etaining strip foundation depth should not be less than (.$ meters.
• 0or the base foundation, reinforced soil compaction shall be smooth, and the
carrying capacity of the same shall meet the design requirements. . 2anel fabrication and installation
• The moulds for the panels will be fabricated with steel plates and subected to
regular inspection and maintenance. Any concrete residue will be removed and the plate brushed with a pre-releasing agent. This will ensure the
smoothness of the panel in compliant with the design requirement.
• The strength and geometry of the mould shall be to the exact dimensions
given in the design requirement.
• The top surface of the reinforced concrete foundation shall be cleaned and a
cement mortar with a mix ratio of ("* added as a first layer. Inspection of the layers shall be done, the roadbed width reviewed, alignment of holes done, the bottom level of the retaining wall checked and if any of the above criteria will not have the standard, the work will be repeated ensuring accuracy.
• The panels shall be mounted in order according to the design document using
small home-made artillery for improved installation efficiency.
• A plumb line will be used after every three installations to check the elevation
and axis of the panels and this ensures uniformity in levels. Any level error will be remedied by the use of the ("* cement mortar.
• Installation seam should be uniform, smooth and beautiful.
• The settlement oint of ($mm will be created and will run from top to bottom
throughout the height. . 6aying bar strips
• The geobelt will be staggered according to the specification. 1eep holes shall
be created during the laying of blocks.
• The bar strip will be connected to the panels using its tip which shall be tied to
the reserved holes of the top and bottom panels.
• It should be reinforced with a radial fan laid on the levelling filler so as to
prevent curling or bending.
7. 0iller acquisition, paving and compaction
• The filling material will be obtained locally and should meet the design
requirement. It should not have other impurities such as roots, grass and other debris.
• 'einforced filler paving and compaction will be done i n layers of equal depth
with each layer having strips tied to the panels.
8i9 3ischarge" The distance between the offloading equipment and the panel distance should not be less than (.m as a requirement. This is because the pressure generated by the machine could interfere with the alignment of the panel. A certain thickness of filling material will be established so as to avoid interference of the geobelt by the lower ribs of the equipment.
8ii9 2aving" The paving will be smooth and uniform. The paving equipment will also be at least (.m away from the panel. A distance of (.m will be left because paving that space with heavy equipment could interfere with the panels. Instead, this part shall be compacted with lighter equipment such as pedestrian roller. 2aving shall also be done perpendicular to the panel and this also helps straighten the geobelt.
8iii9 !ompaction" !ompaction of the filled material within (m of the panel shall achieve :#% and this need to be done through pedestrian roller or other lighter equipment. 0rom (m of the panel, :% of compaction shall be achieved and this will be done by heavier equipment.
o 0illing shall be done in layers of between #$cm-#cm thick. 3uring
compaction, the equipment shall not stopped once or have its direction changed abruptly on non-compacted filler. This could interfere with the geobelt placed under the filler.
o !ompaction shall be started centrally and gradually rolled towards the tail of
the geobelt. Then compaction near the panel will be done last. ;. 5iscellaneous
• 5iscellaneous works shall commence upon completion of the whole
re-wall structure inclusive of backfilling works.
• The miscellaneous works are the flexible pavement, drains and road furniture.
• There shall be a proper drainage system within the construction to drain any
interlayer water.
Materials and Equipment
quipment
nu$%er E&ui"$ent 'uantit (
Re$ar)
( 6oader ( 0or filling
# (<T 'oller (-# 0or soil compaction
* &mall compactor # 0or compacting the soil within (m of the panel
crane ( 0or panel shipment if need be
&mall artillery #- 0or panel mounting
proect manager proect technical director eld technicians site inspectors eld test members #andymen $ar strips laying class Transport vehicles class Prefabricated panel and installation class "achinery class
; truck ( 0or transporting panels and other
materials
< Tipper -< 0or transporting the filling material
5aterials"
The materials used shall comply with the design requirements and they are as follows"
• !AT*$$#$/ type plastic composite reinforcement belt 8=eobelt9 • =eotextile
• 0illing material
• 0ilter material 85ainly gravel9 • 0oam 8for expansion oints9
Labour Organization
Construction labour organisation:
Quality control
• 'einforced earth retaining wall construction shall be strictl y done in
accordance with the design documents.
• The operations on the ground shall also be done in accordance with the
design document and if by any chance any adustment has to be made due to the ground conditions, it shall be done on approval by the resident engineer or his representative.
• Temporary and permanent drainage works needs to be put in place before,
during and after construction. The filler surface that has not been compacted should be covered with plastic sheeting in case of rain indication.
• 2anels shall be created according to the design document. Any defective
panel shall not be transported to the site.
• The safety of the reinforced retaining wall is dependent on the quality of the
filling material and its compaction which must be based on the design
document. 'egular and consistent inspection as well as following construction rules put in place ensures a good quality of work.
• All batches of bar strips transported to the site shall be sampled and checked
for breaking strength and elongation.
• The panels used must be smooth and of the appropriate si+e to enhance a
straight vertical expansion oint.
Security measures
• &afety technical tests must be carried out step by step and very often and
the record kept. !lear safety measures must be put in place to ensure safe working environment.
• The construction site should be planned to adhere to the local fire
protection by-laws. 2roper plans should be put in place to ensure fire safety as well as develop fire contingency plans.
• &ince the work will be done near a busy road, the working area will be
barricaded using temporary barrier to stop non-working personnel and vehicles from getting to the site which is risky.
• 2roper signs will be put in place forewarning the general public and other
personnel of excavation danger in the barricaded area and this will work for good to all.
• A good site plan will be established to ensure safety on this site as well as
personal protective gear for his own safety and the person in charge of this site will ensure that everybody follows that directive.
• &ite clearing may be required as well as excavation and therefore the
personnel operating the excavator will have prior training.
• The excavator itself will have prior checking before beginning work as a
safety measure.
• /efore the start of excavation, any underground service will have to be
identified and the risk assessed and the correction m easures undertaken.
• The control measures for the work will be monitored in the course of work
performance. 2roper communication will be established within the site before and during the working time to ensure safety on site.
• The manoeuvring of the excavator on this site will be undertaken under
controlled condition to reduce the risk to other site users and also to
ensure that it does not come into contact with other services going through this site if present.
• The concrete for the re-wall foundation will be prepared under controlled
condition and brought to the site by a mixer truck. A pump will be used to place it on the already prepared and reinforced foundation. The pump operator will handle the delivery line in the placement to the said area.
• The work environment will be assessed for the overhead services which
may interfere with the concrete pump boom and this will help the operator to find an alternative route for the boom to place the concrete.
Environmental protection
3uring normal maintenance of the construction equipment, it)s likely to have oil waste and this should be collected in containers and disposed appropriately away from the site in accordance with local regulatory authority. nvironmental
pollution shall be avoided at all cost.
>oise on the site shall be kept under control as well as dust. After the completion of work, the site shall be cleaned and the materials cleared and disposed
