Re-wall Methodology

RE-WALL METHODOLOGY: OUTER RING ROAD-NAIROBI

Introduction The reinforced earth retaining wall is a coherent gravity structure engineered to resist specific loading requirement. The primary components of this re-wall will consist of alternating layers of backfill and high-adherence soil reinforcing tapes or strips to which a modular precast concrete facing is attached. Its strength and stability will be derived from the frictional interaction between the backfill and the reinforcements, resulting in a permanent and predictable bond that creates a unique composite construction material. A mechanical connection between the facing panels and the soil reinforcing strips will will be achieved by way of a special special tie strip embed. embed. This connection creates a system that is technically sound and highly reliable because of the improved mechanical properties of the soil. The inherent strength and flexibility of  the overall wall system gives designers a powerful way to economically solve difficult stability issues for structures subect to flooding or other dynamic forces, or those in seismically active areas. !ompared with other types of retaining wall, the reinforced earth retaining wall has the following maor advantages" •

It is advantageous over cast-in-place wall, both in construction time and 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

•

retaining wall can save up to #$% of the cost. It is also flexible, making it possible to build directly upon compressible soils

•

and therefore deep excavations need not to be done thus reducing cost. The wall has high load-carrying capabilities, both to static and dynamic loads as a result of reinforced earth through several layers of high strength tensile

•

strips. &ince it uses prefabricated components, it is easy to install therefore making it

•

rapid and predictable in terms of construction period. It is aesthetically appealing since the facing is highly suited for architectural finishes. The regular shape of the blocks and their arrangement 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 proect, 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.

The "roce of o"eration Foundation engineering and precast panel

Panel mounting

Panel checking

Panel adustments

Laying of geobelts

Checking geobelts

!dusting geobelts

Spread lling material

Check lling material

Filling material adustment

Compacting lling material materui

Check degree of  compaction and

"ore compaction and panel adustment

 Top level achieved

Subsidiaries and defence, drainage works

Completion and inspection

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.

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 subected 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 •

8i9

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. 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

8ii9

interference of the geobelt by the lower ribs of the equipment. 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

o

achieved and this will be done by heavier equipment. 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

o

geobelt placed under the filler. !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 rewall 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 

nu$%er

quipment E&ui"$ent

'uantit

Re$ar)

(

6oader

( (

0or filling

#

(