Design, Construction and Behavior of Bored Cast In-situ Concrete Piles in Bangkok Sub Soil

This paper briefs design considerations, construction methods and materials, static load test results and pile integrity test results of the cast in-situ bored piles constructed as foundation elements for a wastewater treatment plant. The treatment plant is located in Bangkok, capital of the Kingdom of Thailand and is to serve about 195,000 inhabitants of the city. A total of 402 piles, 296 nos. of 1500 mm diameter and 96 nos. of 1000 mm diameter, were designed to carry the whole structural load of the treatment plant. Maximum working load on individual piles was designed to be 1000 tons and 500 tons for 1500 mm and 1000 nun diameter pile respectively with a safety factor of 2.5. Initially the pile toe depth was designed to be 60m below the ground level and embedded into hard clay for 1500 mm diameter piles while the smaller diameter pile embedded into second sand layer at a depth of 53m and base was not decided to be grouted. Pile load test results on fully instrumental pilot piles showed the failure well before reaching the designed test load. Piles were re-designed and pile toe depth was set to be 55m, embedded into dense sand layer for both sizes and base grouting was decided to be done for all piles. Proof load test results performed on four working piles (contract piles), two for each size, produced well acceptable results conforming to the design and structural specifications and requirements. However, settlements observed were higher than that observed for other projects in the vicinity. Base Grouting was done using tube - a manchette method. A maximum volume of 500 liter of cement grout (w/c ratio ~ 0.5) or maximum grouting pressure of 40 bars was used as limiting criteria. However, maximum pressure of 40 bars was hardly achieved. From the proof load test results ultimate load capacity was estimated and compared using different methods suggested by previous researchers. Integrity test was decided to be performed on each pile and results available currently are summarized