The Dutch pile design method, NEN9997-1, classifies screw and screw-injection piles as fully displacing. For these pile types, the design code prescribes a base factor αp 0.63 and shaft factor αs in sand of 0.009. However, an ongoing TU Delft research programme on these pile types has indicated findings conflicting with NEN9997-1. This thesis investigates whether screw and screw-injection piles should be classified as fully displacing piles and how the design process can be improved, through the interpretation of existing load tests.
The thesis compares measurements of pile load tests to the load-settlement behaviour of fully displacing and (partly) soil replacing piles, including the effect of limiting qc to a maximum of 15 MPa for shaft friction. From appropriately instrumented tests, αp and αs factors are determined and compared to the prescribed factors. Additionally, a shear box test is performed in order to investigate debonding between the grout body and steel tube of a screw-injection pile.
Interpretation of the load tests strongly signify that the load-settlement behaviour of screw and screw-injection piles does not resemble that of fully displacing piles, but rather (partly) soil replacing piles. Determined values of αp range from 0.23 to 0.35, while values for αs in sand range from 0.011 to 0.012. Limiting qc along the shaft is shown to produce less realistic capacity and behaviour predictions when compared to measured test data. The shear box experiments indicate that in dense soils with high qc values, debonding between the grout and steel tube of a screw-injection pile under high load can occur. ... Read more

The interaction between fractures and the associated effects are studied in fields like geothermal engineering, seismology, volcanology and geo-engineering. Fractures can massively influence the permeability and porosity in a rock formation, reducing resistance to flow. However, to improve permeability, multiple fractures must connect to each other. Therefore, it is important to understand the effects of a stress field under varying orientations and how it influences new and existing fractures. Brazilian disc tests were filmed and performed on 18 Indiana limestone samples, after which 13 samples were fractured a second time under orientations varying from 20° to 90°. Afterwards, video footage of the tests was used to study fracture propagation and fracture roughness. Analysis of the results showed that four distinct types of fracture behaviour occurred. Each type was generally displayed between certain angles. Case 1, under 30° shows reactivation of the original fracture. Case 2, between 30 and 45°, shows largely reactivation of the primary fracture but new secondary fractures towards the ends of the sample. Case 3, between 45 and 60°, shows the primary fracture closing and formation of secondary fractures near the centre of the disk. Case 4, from 60° onwards, shows the primary fracture close completely while a new fracture forms perpendicular and independent of the first. The results imply that initiating a stress field in a certain orientation has differing consequences. A stress field more parallel towards the original fracture causes reactivation of the fracture, without much impact on the permeability. However, a stress field initiated perpendicular to the primary fracture causes a new fracture to form, independent of and straight through the primary fracture. This is likely to increase permeability and therefore reduce resistance to flow. ... Read more