Wet Grab Samples vs. Cored Samples as QC/QA Methods at the Rio Puerto Nuevo Project in San Juan, PR

Deep Mixing Method (DMM) for the Rio Puerto Nuevo Project in San Juan was chosen by the Corps of Engineers to improve the soils adjacent to a 92" forced sewer main relocation and to improve the soils for the base of a new drainage channel. The soils consisted of sandy fill, soft clays, organics and stiff, plastic clays. Production comprised over 3,000 DMM elements, installed to a maximum depth of 57 feet deep. Each element consisted of two 5.5' diameter overlapping columns installed simultaneously. The layout of the elements was such to meet the 100% Area Replacement Ratio required by the design. Wet grab sampling and UCS testing of the retrieved specimens were designed as the main QC/QA method. Upon completion of production, approximately 3,000 specimens were cast. The contract also required continuous coring of at least 12 randomly selected DMM elements and the testing of 8 cored specimens per bore for strength assessment. This paper will illustrate means and methods used in field to collect the wet grab and the cored samples, focusing on the significant differences between the two UCS data sets.