This thesis aims to explore the influence of borehole alignment accuracy and other soil and pipe parameters on the pullback forces during the pullback phase in Hor- izontal Directional Drilling (HDD) operations. To that end a model inspired by PipeForce V1 was implemented and expanded upon in Python. The model was used to calculate the pullback forces based on the measured product pipe naviga- tional coordinates obtained from actual HDD projects. Calculated pullback force data was compared to actual measurements. It was found that pullback forces tend to decrease with increasing borehole alignment accuracy. The extent of the influ- ence depends on the length of the installation under consideration. Furthermore, through analysing ballasting and specific gravity of slurry, it was found that a bal- ance between those factors resulted in a decrease in the maximal pullback forces, through optimising the effective vertical force on the product pipe. Lastly, it was found that the originally proposed model PipeForce V1 should not be applied to longer installations due to an almost quadratic growth in one of the calculated fac- tors, which was not checked for in the original publication.

In this thesis the geotechnical bearing capacity of old timber piles in Amsterdam is studied. This is necessary because many structures such as quay walls, bridges and houses in the (historic) city centre of Amsterdam are founded on timber piles with ages ranging between 80 and 300 years old. The assessment of the foundation is currently done using many assumptions, these are needed because the piles are not easily accessible and old construction drawings are not always available or accurate. Furthermore, the effect that bacterial degradation of the wood has on the interface friction between soil and wood has never been studied in detail. In the assessment it is currently assumed that degradation has no effect on the geotechnical bearing capacity (Kalt and Dusseldorp (2018)), while in the old Dapperbuurt tests it was found that old piles had a reduced shaft capacity of 40% (Korff (2013)). The study is split into two parts; firstly a laboratory study into the effect of bacterial degradation on the interface friction between sand and wood has been performed, and secondly a sensitivity analysis into the geotechnical bearing capacity of timber piles in Amsterdam soil has been carried out.