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Royal Boskalis Westminster nv is an international group with a leading position in the world market for dredging services. In most practical cases a jet installation or a big discharge aperture is used for the fast unloading of a load of sand. When a relative small discharge opening, without the use of a jet installation, is used to unload a hopper, the unloading time will increase. Uncertain is how much longer this type of unloading will take and what kind of mechanisms play a crucial role in this unloading procedure. The goal of this study is to analyse and describe this unloading process. An attempt is made to model the processes in such a way that an estimation can be made for the unloading time. During this research two sets of experiments were executed, the preliminary and the main experiments, each with a different experiment set-up, to obtain more insight in the unloading process. The goal of both sets of experiments was to get a two dimensional view on the sand-water-processes above the discharge opening. The most important parameters which are varied during the experiments are the width of the discharge opening (wdo) and the height of the sand at the start of the unloading process. Out of the preliminary and main experiment comes the qualitative description of the unloading process in time: 1. Coming into existence of a dome. 2. The failure of the dome. 3. Fluidization of sand mass. 4. Break through of water through the sand-water mixture 5. Breaching of sand from the walls at both sides of the discharge opening. For two components out of the unloading process a first set-up for a quantitative model is made with as final goal a good prediction of the total unloading time of a barge. These two components are: 1. The dome that comes into existence 2. The moment of failure of the dome With the theory in this thesis and the data of the executed experiments can be concluded: Total unloading time: o The total unloading time decreases for an increasing width of the discharge opening Expanding velocities: o A new approach has been developed for the single particle mode in which the perpendicular expanding velocity for the roof of the dome (β=180 degrees) is approximately 2.2 times larger than expanding velocity perpendicular to the vertical walls (β=90 degrees). This new approach fits a lot better with the data out of the experiments for the expanding velocities of the dome, but is not yet completely satisfying.

Pile foundations are widely used, mainly to transmit structural load to an underlying stiffer soil or rock. This limit state load a certain pile can sustain without failure is known as pile ultimate bearing capacity. During design stage load-tests are performed in-situ on test piles to determine, among others, the value of the bearing capacity. Commonly static tests are performed as they provide the most reliable data. Dynamic tests are much more cost-effective but have a series of shortcomings, mainly the fact that they introduce stress-waves on the pile and that require calibration with the static values. To overcome both nature-kind problems, a new type of test in-between the previous ones, i.e. the pseudostatic test, has been developed. It is still a dynamic test but the loading pulse lasts longer (70-150ms), 20 times the dynamic pulse, emphasizing the static component. Hence, it is both an economical and reliable option as requires no calibration with the static load-displacement curves. Therefore, it is interesting to get more insight on it. Two main factors can influence the bearing capacity of a pile measured on the in-situ tests, namely, loading rate and excess pore pressures. In cases like The Netherlands, where end-bearing piles are driven into saturated sand, these two concepts may play an important role. A previous study had been carried out in dry sand and did not find a remarkable loading rate effect. However, for the case of saturated sand the soil response remains unknown. This research investigates the topic, the objective is to get more insight on the excess pore pressure generation and dissipation, evaluate the static-pseudostatic correlation and investigate the possibility of providing effective predictive tools. The research has been structured in three parts. First a series of experimental scaled tests have been carried out for three loading rates: a CPT (20 mm/s), a static test (1 mm/s) and a pseudostatic test (up to 250 mm/s). The sample consisted in saturated sand that was prepared by means of a fluidizaton-vibration system. Standard sounding rots with a piezocone acted as the pile; five values were recorded: force on the pile head, shaft friction, tip resistance, displacement and acceleration. Later on, the performed scaled tests have been modeled analytically and numerically. An analytical model based on the cone model of Wolf has been developed. Only the soil underneath the pile tip is considered and it is modeled as an elastoplastic material under static fully undrained loading followed by consolidation. PLAXIS is the program used for the numerical model.

Pile load tests are commonly used by engineers to determine its bearing capacity. At present, there are three methods of pile load tests: the static, the dynamic and the quasi-static test. The static pile load test is done by applying an axial load on the pile with a long duration. The dynamic and quasi-static tests are done with an impact load on pile head of very short duration. However, the required force pulse in the quasi-static test is longer than in the dynamic test. This research focuses on the comparison between quasi-static and static tests. An important aspect in order to verify the results of quasi-static application with respect to more widely used static loading. The results of quasi-static tests have both static and dynamic components. Then, in order to convert the results of a quasi-static test to static pile bearing capacity, the dynamic component (inertial and damping effects) in the soil responses have to be understood. The effect of generates pore water pressure and its dissipation during pile penetration are unclear and can limit the interpretation of the results of a quasi-static test.