Influence of grout injection parameters on shaft bearing capacity of screw displacement piles

This document describes the test program that was conducted in 2021 to investigate the influence of grout injection
parameters on the shaft bearing capacity of screw displacement piles. Grout variants considered were water/cement
ratio, blend composition and flow rate. This resulted in 5 groups of 3 test piles with more or less the same grout
parameters. Other installation parameters were kept constant. Back flow grout was sampled to determine composition
and properties. Static load tests in tension until failure were used to determine the shaft bearing capacity of the test
piles. In total 7 out of 15 test piles were extracted afterwards to establish the pile diameter. Also the annulus of the
extracted piles was cored with the purpose to obtain the shear properties of the grout/concrete interface of the piles. It
can be concluded that the range of water/cement ratio’s applied in the test program did not have a substantial influence
on the bearing capacity of the test piles and that the applied highest grout flowrate seemed to be at the limit of becoming
influential. Furthermore it was found that the empirical cone resistance factor for shaft resistance (αt according NEN
9997-1) is in compliance with the generic value of 0.009 for sand layers for this type of pile, provided that a limit value
of 15 MPa for the cone resistance qc is not applied and provided that the shaft bearing capacity is computed based on
the outer diameter of the screw tip.