CONSTRUCTION ARTICLE                        

SETTLEMENT OF 12 STOREY BUILDING IN BANGKOK (Part 2)

Temporary measures

Since the building was settling at the maximum rate around the service-core area, it was considered imperative to effect the slow down of the rate of settlement in that area immediately to correct the tilting, while permanent solutions to the problem were being levelised to minimize the structural damage. Some 300 eight-metre wood. en piles were driven around the back of the service core. Reinforced con­crete cap was cast on top of these piles and connected to the. elevator shaft base by tie rods. Timber struts were connected between the pile cap and second and first floor beams, as shown in Fig. 6. This operation was effective in slowing down the rate of settlement in that area and there was an immediate increase in the rate of settlement in the other areas. The tilting was carefulIy reduced automatically, too.

Permanent underpinning

Due to the excessive movement of the foundation it was concluded that the piles have failed and must not be relied upon to carry the load any more on a permanent basis. New pilings of suffi­cient capacity and numbers were de­signed to take over the entire load from the old ones.Due to the limited head room and the need for rapid progress, two types of underpinning were used - namely, around the old pile cap system and through the old pile cap system. Both systems had the same working capacity of 100 ton/pile and could be inter­changed to permit flexibility of action in order to expedite the underpinning process. Around pile cap system

Steel piles made from 3 pieces of 10­ inch channels welded together and driven to - 25 m were tested to withstand 240 tons. These types of piles were driven as near to the pile caps as possible, and were capped by reinforced concrete slabs, 0.75 thick, which in turn were connected to the old pile caps underneath by means of high tensile steel anchorages (secured to the old pile caps by epoxy bonding in 4 inch holes diamond-drilled into the old caps. Pull out tests made of these anchorage reached 100  tons and four anchorages were used  for each pile.

figure 3 :   around pile system                    figure 4 : Anchorage and locking beam for through 

                                                                                                       pile cap system

Through pile cap system                               I

14-inch diameter holes were drilled through the old pile caps which were s 2.50 m thick. Four 4-inch holes were drilled around the 14-inch holes. A special anchorage was epoxy-bonded into these holes. These anchorages were first used to secure a jacking portal across the 14-inch hole. A 12. inch steel tube pile was jacked into the soil through the 14-inch holes. The jacking was continued until a resist­ance of 200 tons was achieved. The soil inside the tubes was extracted and the tubes filled with concrete. The tube piles were secured to the pile caps by locking beams  which were bolted to the jacking anchorages. The space between the tubes and the caps were later grouted. This gives protec­tion against corrosion as well as adding to the bond between the pile and the Cap. The locking beams were then con­creted over entirely for complete pro­tection.

figure 4 :through pile cap system        figure 5 : Holes drilled through pile cap for piling

Repairs of structural damages

After the completion of the under­pinning process, repairs were made to the structural and architectural dam­ages. Small cracks were repaired with epoxy grouting. Big cracks were open­ed up and re-cast. Badly damaged areas were completely demolished and re­load tests and later observation.

The building load-tested with sand bags to the equivalent of 150% of the design live load for one week. leveling targets were fixed to all columns and Ievel checks were carried out every month ever since. No further move­ment was detected.  back to settlement of 12 storey building in Bangkok(1)

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