The initial research results on the improvement of offshore axial pile capacity calculation using CPTu data at block A, offshore Vietnam

Tóm tắt

This paper presents the use of CPTu data in calculation of offshore axial pile capacity based on the CPT-based methods recommended in Appendix C of API RP 2GEO (2014) which are the Simplified ICP-05 Method (Method 1); Offshore UWA-05 Method (Method 2); Fugro-05 Method (Method 3); and NGI-05 Method (Method 4). Formerly, the strength values of cohesionless layers were usually taken from onshore laboratory results or if there were none done, the values were generally assumed based on recommendations of API RP 2A-WSD (2000) standard which often resulted in unconservative axial pile capacity. With the availability of CPTu data which better reflects the in-situ soil conditions, the selection of design parameters for cohesionless layers is improved and consequently, the improved axial capacity calculation both in tension and compression. The improvement in predicted axial pile capacity allows better pile design (for example, choice of pile length, optimization of pile diameter) and hence the economical aspects of the final design at a later design stage. Results from the analyses by CPT-based methods indicate that Method 1, 2 and 3 produce comparable results of capacities in both compression and tension, whereas Method 4 shows somewhat a deviation from the other 3 methods. Hence, a conservative approach to using the capacities calculated by method 4 and especially the API RP 2A-WSD (2000) method should be exercised properly by applying appropriate safety factors