Study of the relationship between sand relative density and the sandy soil plug in the sampler of the dynamic penetration test (SPT)

• Grant number: 12/13364-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: September 01, 2012
• End date: August 31, 2013
• Field of knowledge: Engineering - Civil Engineering - Geotechnical Engineering
• Principal Investigator: Cristina de Hollanda Cavalcanti Tsuha
• Grantee: Lucas Manhani Galego de Lima
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

The SPT test is the most used method of soil in situ investigation in the America to the estimation of soil parameters used in geotechnical projects, and also for the design of foundations. In Brazil, this test is performed according with the Brazilian standard NBR 6484 (2001). It is observed in the field that when SPT test is performed, there is aportion of soil that penetrates into the sampler tube, which in many cases hasthe penetration length different from the 45 cm of the sampler penetration into the ground. During the SPT sampler penetration into dense sand, the inner soil column develops friction between its sides and the tube, and the soil attaches itself to the inside wall of the sampler and both move as one unit, and a tip of soil is created (plugg).Differently, when the SPT sampler penetrates into loose sand, the soil moving separately from the sampler during the test (unplugged). The length of the ground penetrated into the sampler tube after a penetration of 45 cm into the ground, is known as recovery of the sample. Considering thelength of the recovery of soil sample it can be determined the ratiobetween frictional and the tip resistance of the sampler during the SPT test, which isinversely proportional to the length of the sample recovery. This ratio could be used to predict pile foundation capacity.However, to verify the variation of the recovery length with thedegree of compactness of the sand penetrated, it is necessary to perform SPT tests into uniform materials (100% sand) and with known degree of compactness. For this reason, in this investigation it will be performed SPT tests in tanks filled with sand mass prepared with different relative densities to verify the influence of the sand compactness on the recovery length of the SPT test sampler. (AU)