In order to build new offshore breakwater on weak ground, prefabricated thin-walled structures are often considered as its foundation. Integrated into a preliminary design study for a prototype breakwater to be built, a series of geotechnical centrifuge model tests are carried out to investigate the penetration behavior of a large thin-walled ellipse suction bucket into a layer of thick muddy clay. The bucket foundation is first sunk into the muddy clay layer under its self-weight during the elevation of centrifugal acceleration to the appointed value. Then an external sinking force is applied in flight on bucket by a driving actuator of large travel. During this penetration stage, the internal compressive strains of wall and partition boards are measured against bucket displacement along with the external force applied. After penetrated through the clay layer, the bucket base is rested upon a silty clay layer. It is found that a turning point occurred on the relationship curve of total resistance with penetration displacement, indicating the contacting of the soil within bucket with its inner ceiling. Accordingly, the value of resistance at the turning point is specified as the critical resistance of penetration, which governs how much vacuum value is utilized in its embedding process by means of vacuum method. Also, the friction profile with penetration displacement is also analyzed of outside wall and inner diaphragms of bucket foundation.

Centrifuging for Penetration of Ellipse Suction Bucket of Breakwater into Clay Ground

A centrifuge modeling for a new-type sheet pile bulkhead is presented in the paper. As one of the most typical waterfront constructions of the bottom-fixed port marine pier structure, sheet pile bulkhead is widely used in small size piers or medium size piers. It is usually composed of two rows of sheet pile walls connected by tie-rods, namely, the front wall for retaining soil and the anchor wall. A new type of sheet pile pier structure, with retaining structure up to 18 m, is being devised in the construction of new ports in China, especially where the muddy or sandy seashore is prevailing without rock foundation or very stiff soil foundation. The distinct feature of this new sheet pile pier structure is to add a row of barrier piles in between two rows of sheet pile walls. With the presence of barrier piles, lateral earth pressure acting against the front wall will expectantly be reduced that it can withstand much higher height of soil than the usual sheet-pile wall. But the lateral earth pressure acting on both sides of barrier piles is unknown, which leaves much uncertainty in the structural design. In order to better understand the contribution of barrier piles in the reduction of lateral thrust to the front sheet-pile wall and to provide experimental data to optimize the current design of this new structure, a sheet pile pier of this innovative structure has intensively been studied by centrifuge modeling with respect to a prospect pier structure design. One model test and its result is reported in the paper in which lateral earth pressure acting on barrier pile and its response of bending moment are measured by means of custom-made miniature earth pressure cells and strain gauges. An insight of the inherent working mechanism of barrier pile in this new structure is gained from the analysis of the test results.

Y. J. Zeng

Papers

Centrifuge modeling for a new type sheet pile bulkhead with barrier piles