Abstracts Engineering

An investigation of the overlapping passive zones using a novel geotechnical centrifuge model:

by PT Hopman

To improve the design of soil retaining walls in narrow trenches, a design optimization tool is introduced by Hosseinzadeh and Joosse (2015). This design optimisation tool is an intensification factor on the passive earth pressure coefficient Kp, that includes the effect of overlapping passive zones. The authors argue that the passive earth pressure coefficient due to the overlap of passive zones is larger compared to the passive earth pressure coefficient in case of unrestrained passive zone development. The intensification factor XKp is defined as the ratio between the unrestrained ultimate passive capacity and the restrained ultimate passive capacity, the magnitude is dependent on the dimensions of the narrow trench. The authors observe that the intensification factor increases non-linear when the dimensions of the trench decreases. The numerical study of Hosseinzadeh and Joosse (2015) is based on theoretical assumptions of the Hardening Soil model in the Finite Element Modelling (FEM) software Plaxis 2D. To improve the understanding of the intensification effect and to validate the numerical study, a novel physical scale model is developed which models the unrestrained passive zone development and the effect due to the overlap of passive zones. To simulate realistic stress levels in the model, a geotechnical centrifuge is used where earth’s gravity is enlarged by high speed rotation of the model. Multiple sand characterization tests are performed to obtain the parameters of the Delft Centrifuge (DC) sand. Furthermore, interface characterization tests are performed to obtain the friction parameters playing a role in the physical model. Various centrifuge tests at 80g and 100g are performed in the geotechnical centrifuge facility of the Delft University of Technology. An actuator in the strongbox is connected to a stiff wall. During translation of the wall towards the soil body, the load and the wall displacement are measured. The wall represents a prototype embedded length (d) of 5 m in all the tests. Restrained passive soil behaviour is modelled symmetrically in the strongbox and the width (w) of the narrow trench is varied in the test series. An ultimate passive load is measured by the plateau state and visible by the full development of the shear band for w/d ratios of 6.4, 3.0, 2.0 and 1.5. It can be concluded from the physical model tests that the intensification effect is observed in the model results. The ultimate passive load (indicated by the plateau state) is larger in models with a smaller w/d ratio. The intensification factor displays a non-linear increasing trend for decreasing model dimensions w/d. The curvature of the trend line is similar to the trend observed in the numerical study by Hosseinzadeh and Joosse (2015). This thesis shows however discrepancies between definition and the absolute values of the intensification factor of the numerical model and the physical model. The physical model tests show significant larger ultimate passive capacities and intensification factors compared to the… Advisors/Committee Members: Askarinejad, A., Hicks, M.A., Bakker, K.J., Everts, H.J., Den Arend, D.E..