Method Statement for Base Slab Modification of Retaining – Civil Engineering

2. Summary of Activities:

(i) Temporary Protection and Supports for Equipments/Structures.

(ii) Construction of Shear Keys

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(iii) Concreting of Buttress Wall

(iv) Construction of New Base Slab

(v) Protective Coating System

(vi) Handing Over

3. Procedure for the Temporary Protection and Supports:

(i) Necessary protection shall be provided for the existing electrical panel and cable trays.

(ii) Electrical panels shall be covered by using standard scaffolding system with 18 mm plywood all rounds.

(iii) Independent cable tray supports shall be properly supported while breaking the floor slab.

(iv) The locations of the shear keys shall be marked on top of the base slab and provide supports and protections for the structures overlapping with the shear keys.

(v) Steel staircases fixed on the base slab shall be supported with prop jack while breaking the base slab.

4. Construction of Shear Keys:

(i) Shear key construction sequence shall be strictly followed as detailed below.

(ii) Mark the shear key #1, 2 and 3 on the base slab and break out the slab one at a time using jack hammer without cutting the rebars.

(iii) Sand bags shall be stacked around the slab cut out for the shear key counter weight equivalent to the demolished slab area.

(iv) Cut the rebars at middle of the shear key and bend up in 90° for all access for excavation.

(v) Excavation shall be carried out manually and remove the soil j specified depth.

(vi) Install the rebars for shear key as shown on the drawing and make s the slab rebars into the shear key. Additional lap rebar shall be pr along with the slab rebar.

(vii) Concrete the shear key up to the slab bottom level with the specific concrete and vibrate the same with needle vibrator.

(viii) Follow above procedure for the shear key # 2 and 3. Construct the buttress wall by connecting these shear keys.

(ix) Continue the construction of balance shear keys as explained earlier counter weight sand bags shall not be required after concreting the b wall.

(x) Following construction sequence of the shear keys shall be followed during the construction shear keys and base slab panel concreting.

(xi) After the construction of buttress wall front side shear keys # 6 and 7 shall be constructed at a time and followed by key # 10. Concrete the panel #21 and 22 immediately after the shear key concreting.

(xii) The shear keys # 8 and 9 shall be constructed at a time after completion of the shear keys # 6, 7 and 10 followed by shear key # Follow the base slab concreting as explained earlier.

(xiii) Shear keys # 12 and 13 shall be constructed at a time after the shear key# 15.

(xiv) Shear keys # 14 and 16 shall be constructed at a time after the shear key# 15.

(xv) Construction of shear key # 17 and 18 followed by shear key # 19 and shall be carried out in two stages.

(xvi) The base slab concrete shall be concreted immediately after the casting shear keys inside of each panel.

5. Procedure for the Construction of Buttress Wall:

(i) Mark the wall and rebar position on the face of the retaining wall.

(ii) Drill and fix the starter bars on the retaining all by using chemical anchors.

(iii) Scrabble the concrete surface by hacking on concrete. Break out concrete of slab area as shown on drawing for a depth of 120 mm using jack hammer

(iv) Install vertical starter bars for the buttress wall as shown on the drawing

(v) Install the new slab reinforcements and bend up the lap length connecting remaining base slab rebars.

(vi) Clean the concrete surface and apply the bonding agent prior to concreting the base slab and wall kicker.

(vii) Install the rebars by connecting the vertical and horizontal starter bars.

(viii) Fix the formwork in half height of the buttress wall and tightened by using through tie rods.

(ix) Concrete the buttress walls in two pours by pouring concrete from top and vibrate the same using needle vibrators.

(x) Similarly cast the second stage and allow for curing by using wet hessian cloth.

6. Procedure for the Construction of New Base Slab:

(i) New base slab shall be concreted in nine parts along with construction joints at all around.

(ii) New concrete base slab shall be concreted in panels. The top surface 0 these existing slabs shall be demolished for a depth of 120 mm depth and expose the top layer rebar.

(iii) If corroded rebars cross section area reduced more than 15% of its original cross sectional area, these bars shall be replaced with new rebars.

(iv) Other rebars shall be grit blasted and apply two coats of Zinc rich prime prior to the concreting.

(v) Provide a new layer of reinforcement on top of the existing rebar as shown on the drawing. The additional lap length of the new rebars shall be kept bent up position for lapping to the next slab.

(vi) Clean the concrete surface and apply the bonding agent then concrete the new slab.

(vii) The top surface of the base slab shall be sloped towards the open channels and finished with wooden float.

(viii) Continue the slab concreting in panels immediately after concreting the shear keys inside of each panel.

a) Slab 21

b) Slab 22

c) Slab 23

(ix) Proper curing shall be carried out by pending water on top of the slab.

7. Procedure for Protective Coating System:

(i) The slab surface shall be properly cleaned and remove all the dust.

(ii) All the pinholes and repairs shall be carried out with approved repair mortar materials.

(iii) Primer coating shall be applied on the prepared surface to receive the approved protective coating.

(iv) Approved protective coating system shall be applied on the primer as per the manufacturer’s recommendations.

(v) Allow the protective coating to cure, and then prepare the construction join grooves in straight line.

(vi) Clean the groove properly and apply the approved sealant as per the manufacturer’s recommendations.

(vii) Joint sealant shall be applied on the vertical joint of the buttress wall and retaining wall.

8. Handing Over:

(i) All the temporary supports and protective covering to the electrical panel shall be removed.

(ii) Clean all the repaired area by using compressed air and water washing.

(iii) Collect all the construction related debris and transported to the designate areas.