Utökad utvärdering av CPTu-resultat

Sammanfattning: In Sweden, it is common to use the CPT - Cone Penetration Test when probing in loose soils. This is mainly because the method is suitable for further assessment of soil layer sequences, pore pressure and forming an estimate of the geotechnical properties in-situ. Evaluation of a CPTu sounding in Sweden today takes in most cases place through the computer software CONRAD, which is based on semi-empirical relations. This study evaluates different methods for determining soil layer and classification as well as the density of materials based on results from CPTu surveys. P. K Robertson's methods for soil classification has been compared with CONRAD and verified soil layer sequences through laboratory protocols. A method for in-situ density estimation has also been studied and evaluated. Previous studies have shown that by using signal processing on CPTu data, it is possible to identify changes in soil layer sequence. Thus, a wavelet transform has in this study been used on the SBT index to find positions in which the layer sequence changes. The purpose of the study has been to investigate the validity of the evaluation methods, but also to see if additional information can be obtained without changing either the performance or sounding equipment. The study is based on CPTu data taken from already performed and completed preliminary investigation projects in Central Sweden, which means that no field investigations linked to this work has been carried out. The main conclusions from this study are: • Application of signal processing to CPTu data has potential to evaluate and interpret stratigraphic layers in a soil profile and has in this study identified silt layers • The wavelet transform is efficient to sort out interesting properties in soil based on CPTu results and has the potential to be successfully applied to sounding results performed in coarser soils • Robertson's SBT method for soil interpretation works well as an evaluation method in homogeneous, loose soils • Robertson's density evaluation method works well in homogeneous, loose soils but has problems handling clays with crust characteristics and soils with a high organic content.