# CPT Parameters of Loess Subsoil in Lublin Area
## 2 Materials and Methods  
The basis for the characterization of Lublin loess soils was the results of in-situ tests--CPT and CPTU static soundings carried out in the years 2015-2020 by GeoNep company. As part of the analysis of static soundings, the geotechnical documentation prepared for 152 locations was reviewed (Figure 2), from among which data were collected from a total of 1136 CPT and CPTU soundings with a total length of approximately 8385 m, including loess and loess-like deposits. Static soundings were performed with a penetrometer Pagani T63-200 with a maximum pressure of 200 kN, which was used to press the measuring cone at a speed of 2 cm/s. In the tests, mainly a piezocone with an electronic measurement system (CPT/CPTU test) was used, with automatic data recording every 1 cm. In some tests, a mechanical cone (CPTM test) was used in which readings were taken manually at 20 cm intervals. In the case of both types of tests, the recorded values were the cone resistance \(q_{c}\) and the friction on the friction sleeve \(f_{s}\). The cones used for the tests had standard geometry, which corresponded to the base surface of 10 cm\({}^{2}\), the friction sleeve surface--150 cm\({}^{2}\) and the cone tip angle of 60 degrees. All test parameters were compliant with the standards of ISO 22476-1 [34] and ISO 22476-12 [35]. The analyzed results relate to 2287.2 m of soundings with a mechanical cone and 6097.6 m of soundings with the use of an electric cone, of which 1997.25 m of testing were CPTU soundings during which pore water pressure \(u_{2}\) was additionally measured. The type of cone (electrical or mechanical) used in CPT testing affects the value of the \(q_{c}\) and \(f_{s}\) results recorded. This statement is confirmed by the results of many studies and described, e.g., in [36]. Based on the comparative analysis [37], it was found that for typical aeolian loess soils, the \(q_{c}\) values obtained from the mechanical cone test constitute about 93% of the \(q_{c}\) value obtained when measured with an electric cone. On the other hand, the \(f_{s}\) values obtained from the mechanical cone soundings are more than twice as high as those indicated by electric cone readings. While the difference in the \(q_{c}\) readings can be considered small, the difference in \(f_{s}\) is significant. Taking into account that the friction ratio \(R_{f}\), which is used to identify the type of soil, is determined on the basis of \(f_{s}\), the type of cone used should be taken into account when interpreting the results. The \(R_{f}\) coefficient for aeolian loess determined with a mechanical cone is 2.22 times greater than that determined from the electric cone test [37]. The value of pore water pressure \(u_{2}\) recorded in CPTU tests for aeolian and diluvial loess was close to zero or slightly negative, so there was little suction, which is typical for unsaturated soils. The increase in pore pressure \(u_{2}\) was significant only in the case of alluvial loess. It is also a guideline when identifying facies from CPT soundings. Taking into account the obtained relatively high values of cone resistance \(q_{c}\) and the values of \(u_{2}\) close to zero, for loess soils it can be assumed as a simplification that \(q_{c}=q_{l}\). Only in the  
Figure 2: Location of test points used to plot the subsoil cross-section. rare case of alluvial and older diluvial loess facies, when values of cone resistance \(q_{c}\) are very low, e.g., 0.7 MPa, and values of \(u_{2}\) are relatively high, the difference between \(q_{c}\) and \(q_{t}\) values becomes noticeable, but still remains insignificant. It is very infrequent that SBT chart analysis identifies alluvial and older diluvial loess with very low \(q_{c}\) and high \(u_{2}\) as more sandy soil. Having a large amount of data and referring to the division of loess according to [PERSON], the authors of the present publication developed an own representative cross-section showing the geological structure of Lublin on the western side of Bystrzyca.