Estimation of base grout quantity for cast in situ piles based on field test results

Abstract

Base grout improves the load bearing capacity of a pile and reduces the base settlement. There is no established method presently for the determination of quantity of the base grout. This paper presents a model for the determination of quantity of the base grout and verification of actual quantity executed during the base grouting operation in the field. The depth of the sediment deposit at the bottom of the pile has been observed to vary in the range of 0.3 m to 0.8 m or more for the case study presented. This depth of sediment deposit also depends on the pile drilling method adopted. In this model, it is assumed that maximum depth of deposition of 0.3 m may be allowed for concrete work. Based on the available literature and a Guideline on Pile Construction of Hong Kong, bottom cleaning is required if the depth of deposition is more than 0.3 m. Grout quantity also depends on the diameter and, length of a pile, and number of piles, as well as length and diameter of Tube A Manchette (TAM) Tubes and depth of deposition of sediment which takes place before concrete work execution. A case study has been adopted. Theoretical model has been developed based on the quantity executed during base grouting in field. Actual quantity of base grout shall be more than theoretical quantity due to the possible caving in of the side walls of the piles, increased diameter in the bottom of pile tip with the formation of a bulb at times. Therefore, a variable coefficient ‘K’ has been presumed equating theoretical quantity to actual quantity including loss of base grout quantity. ‘K’ value has been determined at 95% reliability and found to be 1.22. The proposed model for quantity estimation of base grout has also been validated with other field data and the results have been found to be satisfactory.