Risk Based Design of Soil Improvement Strategies

Risk Based Design of Soil Improvement Strategies

De Vries, G.B.

Vrijling, J.K. (mentor)
Van Gelder, P.H.A.J.M. (mentor)
Van der Meer, J.P. (mentor)
Everts, H.J. (mentor)

Civil Engineering and Geosciences

2002-11

In Singapore, large-scale land reclamations are executed, in which among else Van Oord ACZ is participating. The subsoil of these reclamations often consists of soft, compressible materials, such as marine clay. Depending on the clay properties, the thickness of the soft layer and the thickness of the placed sand layer, a certain settlement will occur within a certain consolidation time. To control the occurring settlement and/or to shorten the consolidation time, different measures are available, for instance: installation of prefabricated vertical drains, installation of a temporary surcharge, a combination of vertical drainage and surcharge. The measures above are recapitulated called "soil improvement". During the tender procedure as well as during the actual execution of the reclamation works, it is of great importance to predict the settlement and consolidation time (possibly including a soil improvement) accurately. The main objective was to answer the following question: "Can a probabilistic analysis of the soil parameters and calculation models give a surplus value in the prediction of the settlement, consolidation time and the soil improvement needed?". The conventional method to calculate the consolidation time and the settlement is a deterministic one. From a set of data, a representative value is determined, which is then used in the consolidation calculations. In order to calculate the settlement and consolidation time, with stochastic variables, a Monte Carlo simulation is executed. For this purpose a model has been developed, from which the basic outline is visualised in the left figure. Risk can be defined as the product of the probability of a failure and the results of that failure, expressed in a financial value. In general one should minimise the total costs to obtain an optimal design. The minimum total costs represent the optimum combination of surcharge and vertical drainage. Probabilistic calculations increase the insight in the costs involved in a soil improvement and make an economically optimal design possible."

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TU Delft, Faculty of Civil Engineering and Geosciences, Hydraulic Engineering

Student theses

master thesis

(c) 2002 G.B. de Vries