This paper presents the field investigation of a major landslide that occurred in a newly dredged slope for port development in the city of Tianjin, northern China. The dredged slope comprised underconsolidated soft clay of recent marine and river delta deposits. The landslide consisted of a number of individual slides that occurred sequentially and extended retrogressively and laterally into reclaimed land. It lasted for about 1 h, occupying a plan area that is about 200 m long and 150 m wide in the reclaimed land. The failed soil mass was estimated to have a volume of between 700 000 and 800 000 m3. Part of the failed soil mass slipped into a newly dredged open space in the sea. The distance of the debris travel into the berth was about 80 m. The debris surface had a gentle slope of about 3.0°. The angle from the dredged slope crest to the far edge of the debris was about 6.8°. A common rupture surface was found underneath the debris and above the in situ marine mud. It controlled the inland extension of the slope failure. The landslide occupied an inclined area of between 27 000 and 30 000 m2, with an overall slope angle of about 3–4°. A kinematic model is proposed to explain the extension of the landslide into the reclaimed land. Findings of this field investigation are further used in the companion paper for a theoretical investigation of the mechanism of the landslide. The engineering approach and results presented in this study could be useful in the design and construction of dredged slopes in underconsolidated soft soils.
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