A fine undrained soil at the end of a jacked displacement pile is preloaded beyond its in situ conditions. Hence, the now preconsolidated soil exhibits an unload-reload loading pattern with a slight hysteric loop, resulting in higher Young’s Modulus values.
Chances are that unless you’re a practising geotechnical engineer who designs pile foundations, you did not understand much of it. That’s perfectly reasonable. It’s full of technical jargon that takes students an entire year to fully understand. And yet therein lies the largest problem engineers face.