Standart Penetrasyon ve Konik Penetrasyon Deney Verilerinden Killerin Makaslama Dayanımının Kestirimi

Abstract

The undrained shear strength of cohesive soils (su), which is an important soil parameter to be known in order to design economic and reliable structures, is widely used in the foundation bearing capacity and short-term slope stability analyses. This parameter can be determined by laboratory tests conducted on the undisturbed soil specimen or by in-situ tests. However, nowadays, practical and relatively easy in-situ test methods are commonly preferred to estimate the undrained shear strength of cohesive soils due to the difficulties and inconveniences while taking the undisturbed specimens, conservating the specimens in suitable conditions to preserve the in-situ moisture content, and relatively high costs of laboratory tests etc. For above mentioned reasons, it was aimed in this thesis study to evaluate the performances of the empirical relations proposed in the literature to determine the undrained shear strength of clayey soils by using the Standard Penetration Test (SPT) and Cone Penetration Test (CPT) data. For this purpose, a database was generated by compiling the results of 36 SPT and 17 CPT boreholes in clay levels conducted across Turkey by a private company, as well as the corresponding undrained shear strength and other relevant soil properties.

In the first step, undrained shear strength values were calculated by using CPT and SPT data according to the empirical equations proposed in the literature. These values were then compared with the su values determined by laboratory tests, and the obtained results are discussed. By considering the findings, the best predictive relationships in literature for estimation of su were reserved. In the next step, simple and multiple regression analyses were performed to establish the relationships the best representing the compiled data, and significance tests were employed for the these relationships. It was seen that coefficient of determinations of the relationships determined by performing simple and multiple regression analyses between su and SPT-N, N60 counts and some other soil properties were between 0.70 and 0.81. In the estimation of su values from CPT data, it was found that the relationships in which cone tip resistances (qc and qt) were used as input parameters, had higher coefficient of determinations about of 0.80 than those of relationships obtained for determination of cone factors. Besides, it was seen that the performances of these relationships were slightly better than those derived from multiple regression analyses. From these evaluations, it was understood that the equations formed by using SPT and CPT data directly will be sufficient for the estimation of su of clays examined in this thesis. Particularly, it is concluded that there is no need to use some soil properties which are used as input parameter in relationships to estimate su from CPT data in literature and additional tests are needed to determine.

Keywords: Undrained shear strength, Standard and Cone Penetration Tests, laboratory and in-situ tests, emprical relationship, simple and multiple regression analyses.