PORT WORKS DESIGN MANUAL PART 3 Guide To - The University ...

30According to Bjerrum (1972), //is a function of the plasticity index I p (see Figure 4).The plasticity index I p can be determined from laboratory tests.The profile of shearstrength for each layer of clayey deposit can then be determined from the above relationships.The undrained shear strength, c u9 can also be determined from laboratory triaxial testsperformed under undrained conditions. The testing procedure can be found in Geospec 3(GEO, 2001). Shear strengths obtained from laboratory triaxial tests are usually lower thanthose from field vane shear tests, due to sampling disturbance. The disturbance can bereduced by using piston sampling but the vane shear test results are generally considered tobe more reliable, particularly for sensitive clays (GCO, 1987). Cone penetration tests canalso provide a reliable, quick method of investigating the soil structure, as continuous profilesare obtained. The results of the cone penetration tests can be correlated with the undrainedshear strength; methods of correlation are given in Lunne (1997).(2) Strength of Reclamation FillFill is usually placed in a loose state in a reclamation although it may become densified laterunder the weight of the overlying fill layers (including surcharge, if used). The strength ofreclamation fill adopted in the stability analysis should therefore reflect the strengthappropriate to the state of compaction of the fill at the time.Typical unit weights and friction angles for sand fill and decomposed granite or similar typesof fill for preliminary stability analysis during fill placement are summarised in thefollowing:Bulk density: 19 kN/m 3Friction Angle: 30°Cohesion: 03.1.3 Stability AnalysisFor detailed analysis of the stability of each stage of the reclamation, the methodsrecommended in Section 5.3.5 of the Geotechnical Manual for Slopes (GCO, 1984) should beused.The geometry of reclamation, including side slope, layer thickness and dimensions of berms(if any) should be so designed that failure does not occur. The practical verification of this