Settlement data of the Kiltunnel and the Heinenoordtunnel show that immersed tunnels in the Netherlands have been experiencing much larger settlement than expected when designing the tunnels causing cracks in the concrete and leakages in the joints. Settlements of 8 - 70 mm have been measured at the Kiltunnel and of 7 - 30 mm at the Heinenoordtunnel while settlements in the range of 0 - 1 mm were expected. Both sites are investigated through non-invasive geophysical site investigation method MASW (Multichannel Analysis of Surface Waves) for each 2.5 meter along the length of the tunnel and invasive site characterisation method CPT's (Cone Penetration Tests).The settlement of immersed tunnels is similar to that of a shallow foundation. It can be modelled using the Mayne equation which uses the small strain shear stiffness and the degradation of secant stiffness based on the load compared to the ultimate bearing resistance. The initial settlement can not have caused the settlements that were measured, because the initial settlement have already occurred at this time. The 5% and 95% boundaries of the creep settlements for both tunnels is much smaller than the measured settlements. To see if cyclic loading has an effect on the settlement of the middle section the effect of thermal expansion and contraction of the elements and the cyclic loading of the tides is examined.The expansion of the Gina Gaskets between the flat element and the elements at an angle is between -3 and 3 mm. This expansion and contraction of the Gina Gasket causes a vertical load on each of the edges of the middle element of 268 kN. This means that it does have a small influence on the settlement of both tunnels measured at these joints but does not explain all occurred settlement. For an indication of the settlement of the Heinenoordtunnel and the Kiltunnel under the loading of the tides a few calculations have been performed using an assumed lower bound of 40% and an upper bound of 90% of loading of the tides. At the Heinenoord the lower bound scenario gave results between 4.99 - 7.51 mm, which means that the measured values of around 7 mm are within the range of the results, while the upper bound scenario gave results between 10.05 and 15.57 mm which is larger than the measured values. At the Kiltunnel at location 21 and 23 the lower bound is more accurate, at location 19, 25 and 27 the upper bound is more accurate while for location 29 the measured settlement is somewhere in between the two bounds. At location 19 even the 95 % of the upper bound (21.34 mm) is much smaller than the measured settlement (around 34 mm). The difference in shear wave velocity is not that large and can not explain the large difference in settlement while the information from the CPT's is so limited that it is not possible to determine if there is a difference between location 19 and the other locations.

A time-dependent capacity increase has often been observed for driven displacement piles in sand. Long-term bearing capacity increase after dissipation of excess pore water pressure is referred to as set-up. Significant increases in axial capacity have been reported where the rate of set-up varied between 15 and 75% per log cycle of time.

More economic foundation designs are feasible when set-up is incorporated in pile design methods. The objective of this thesis is to expand knowledge on time-dependent capacity of driven displacement piles and make way for a pile design method that incorporates time dependency of pile bearing capacity.

The time dependency of virgin pile capacity has been assessed in a database study and a scaled test program. 4 scaled closed-ended steel piles were driven in a man-made sand deposit. The virgin capacity of a pile was assessed 2, 16, 31 and 70 days after installation. The 3 m long, 0.15 m diameter piles were statically tested in compression. Strain was measured at multiple locations along the shaft during the load tests. The applied load and pile displacement were measured at the pile head.

The contribution of the pile shaft and pile tip was determined from the strain distribution over the pile length at failure. A trend for capacity increase with time has been found in the database study and the test program. A capacity increase of 13% per log cycle of time was found for the closed-ended piles tested. Both an increase in shaft and tip resistance was found with respect to the reference capacity determined 2 days after installation. The shaft capacity increased on average 18.5% per log cycle of time and an average increase of 9% per log cycle of time has been found for the pile tip capacity. The measured capacity was compared with the calculated capacity determined by the Dutch design code. Considering the measured capacity normalized by the calculated capacity the influence of time is even stronger on the tip resistance than on the shaft resistance for the piles tested. As discussed in the report, there are some uncertainties with the interpretation of the strain distributions over the pile shafts.

The accuracy of the CPT-based design method available in the Dutch design code, method Koppejan, has been assessed from the pile test results in the database. The results were compared with other design methods available. The accuracy of all methods was low. The calculated capacity exceeded the measured capacity up to a factor 3.

Time-dependent capacity increase is a potential mechanism to incorporate in designs of axially loaded driven displacement piles. A trend for time-dependent increase of virgin capacity was found for all the test results considered in literature as well as for the test program conducted. However, the rate of capacity increase was highly variable. More research is required on the mechanism(s) for a better understanding of time-dependent capacity increase. Understanding of the mechanisms will also help understand what factors, and how these factors, influence the rate of increase.