A comprehensive site investigation was performed offshore the island of Chek Lap Kok as part of the civil engineering design studies for the proposed replacement airport at Hong Kong, The program included conventional drilling and sampling carried out from floating craft, as well as extensive in situ testing, including piezocone penetration, field vane shear, and permeability tests. The laboratory testing program incorporated $K_o$‐consolidated, undrained, triaxial compression, extension, and direct simple shear tests, as well as numerous more conventional tests. The thrust of the investigation was the determination of engineering characteristics for two extensive marine clay deposits that are considered critical to the performance of the proposed airport reclamation. One of these deposits, referred to as the upper marine clay, covers the entire offshore portion of the site. It is extremely soft and sensitive, with undrained shear strengths ranging from 3–12 kPa and sensitivities of about 10. The other deposit, referred to as lower marine clay, is medium stiff and overconsolidated, with in situ shear strengths in the range of 40–90 kPa. The results of the field and laboratory tests are synthesized to develop engineering properties appropriate for reclamation design. Correlations between the piezocone data and field vane shear tests are presented, as well as correlations of compressibility parameters with index properties. Normalized strength parameters for the two marine clays are also presented.

A test fill was constructed to evaluate the feasibility of a proposed airport reclamation over extremely soft marine clay. The test fill investigated the feasibility of reclaiming in layers to avoid creation of mudwaves and the effectiveness of vertical drains to accelerate consolidation. The fill was heavily instrumented, and good performance data were obtained. The layered construction successfully prevented mudwaves, and vertical band drains were effective in accelerating consolidation. Sand drains were not effective, due to mud penetrating the pores.

An offshore test fill was constructed over very soft marine clay to help develop and prove construction techniques for a large proposed reclamation project. The fill and foundation soils were heavily instrumented to monitor their performance during and after construction. The instrumentation was used to measure the rate and amount of settlements, lateral movements, and excess pore pressures. It consisted of pneumatic and hydraulic piezometers, settlement plates and pipes, pneumatic settlement gages, inclinometers, subsurface settlement anchors, and surface movement points. Two major constraints of the instrumentation program were the large vertical strains (approximately 40%) anticipated and the need for overwater/underwater installation of many of the instruments. Special installation and protection measures were developed to overcome these constraints. Performance aspects of the instruments are discussed and typical plots of the data are presented. Additional field testing was undertaken during the monitoring period to verify and supplement the data being obtained from the instruments. This testing is discussed briefly.

Nonlinear conditions are implemented in the time domain formulation for the dynamic response of pile foundations previously developed by the writers. Both single and group piles subjected to vertical dynamic load are considered. In the present study, the nonlinear effects in the vertical response are assumed to result from slippage of the pile from the soil. In order to demonstrate the capability of the present formulations and to see the effects of nonlinearity on the dynamic response of pile foundations, pile foundation responses are computed for both harmonic and transient load. Various interesting observations are made based upon the computed results.

The results of an experimental investigation to determine the effects of preloading on the Mohr-Coulomb failure envelopes of cohesive soils are described. In situ shear tests using the Borehole Shear Test (BST) were performed on a number of natural soil deposits. Initially, conventional stage tests were conducted to obtain the failure envelope. Subsequent tests were conducted by consolidating to a higher normal stress than was used in the shear phase of the test. Results are evaluated by examining the relative increase in shearing resistance between the original failure envelope and the prestressed failure envelope. By defining the Preloading Stress Ratio (PSR) as the ratio of the normal stress where shear strength comparisons are being made to the preloading stress, the relationship between relative strength increase and PSR could be determined. The data indicate that this increase may be described as a power function of the form y = ax^b, where a and b are regression coefficients which indicate the rate of increase in strength with increasing PSR. The results for all soils tested displayed a hysteresis between the original and the prestressed Mohr-Coulomb envelopes, with the prestressed envelopes indicating higher cohesion and lower friction angles.