CONSTRUCTION OF RETAINING WALLS

1.0  Purpose:

A brief description of the construction methodology being adopted in the construction of RCC Retaining wall structure is mentioned below.

2.0  Setting out at Site:

The layout for the PCC leveling course is marked on the proposed location taking reference from the project center line, which is already marked along the existing carriage way and approved by the Engineer. The reduced levels of the existing ground is jointly taken with the Engineer’s representative at site and recorded for measurement purpose.

3.0 Excavation for Foundation:

After recording the OGL, excavation is done using excavator/JCB up to the level required as given in the approved drawing. Any unevenness in the bottom surface is trimmed off, and loose earth will be removed manually to attain good finished surface

4.0 Laying PCC Leveling Course:

After excavation is done, layout is marked; the levels and layout are checked with Engineer’s representative. Then shutters are fixed to line, level and verticality. After approval from the Engineer’s representative, PCC will be placed and leveled. Next day shuttering will be removed and curing will be started as per Technical Specifications

5.0 Reinforced Cement Concreting:

a. Reinforcement:

The reinforcement steel bars are cut to size and bent to shape as per the approved bar bending schedule, in the bar bending yard. These bars are brought to the site and tied as per drawings using binding wire firmly for the required line and spacing.

In the Bottom and side faces of reinforcement cage, cover blocks are tied to get the required cover for the reinforcement from the face of the concrete to avoid corrosion, and required reinforcement chairs are provided for supporting the cage.

b. Raft Concreting:

After reinforcement cage is tied, clean and surface oiled shutters are fixed to line, level and verticality, and any gaps are packed for leak proof.  Before concreting, all arrangements will be checked as per check list and as per Technical Specifications. Expansion joints shall be provided approximately at every 12mts interval. Then concrete is poured in layers and well compacted with the help of needle vibrators. Before pouring the fresh concrete the surface is made wet to avoid water loss in the fresh concrete. The workability of concrete is checked by slump test in the site itself and also cubes are cast in the site for checking the strength as per MOSRT&H specifications. On completion of concrete up to stem, starter course, Shear keys are provided on the top surface.

c. Stem Portion Concreting:

The shutters are fixed to line and verticality in outer side and battered in inner side (Road side) as per drawing. These shutters are held in position using tie rods, clamps, M.S. Pipes, adjustable props and clamps at regular intervals. The gaps in the shutters are packed with foam sheets, and putty to make leak proof.

After approval from the Engineer the concrete is placed and compacted as explained earlier.

d. De Shuttering:

All vertical shutters are removed 24 hours after concreting.

6.0 Weep Holes:

Weep Holes will be provided at 1 m c/c spacing in a staggered manner, using 100mm dia AC Pipes in 1:20 slope as shown in the drawing.

7.0 Expansion Joints:

Generally expansion joints are provided approximately 12m interval (or) at the change of the section whichever is lesser for the whole cross section with 20mm thick Bitumen impregnated boards.

8.0 Curing:

Curing will be started from the next day of concreting of the particular member till 14 days using Hessian cloths or by pond arrangements as per Technical Specifications.

9.0 Backfilling:

Backfilling behind the walls will be done in layers as specified in the MORTH Specifications.