I have conducted static pile load tests on model pipe piles (diam. of 60.3mm and wall thickness=1.6mm) in a calcarenite. The load-settlement curves can be seen in the attachment. All curves demonstrate significant increases and decreases in the applied load with further penetration. There is no ultimate limit load. For design purposes, should one consider the peak or minimum values? I will appreciate if some normative references could be provided.