Analysis of Piled-Raft Foundation for CAI MEP Container Port, Vietnam

During the last decade, a series of ports are being built along the Thi Vai River in the Mekong delta approximately 80 km southeast of Ho Chi Minh City, Vietnam. The ports are built on reclaimed ground over an about 30 to 40 m thick deposit of soft, normally consolidated, compressible clay deposited on dense to compact sand The deep foundation system typically used for buildings in this region consists of pretensioned spun high strength concrete piles driven to significant toe bearing in dense soils. Because of the anticipated significant costs of this solution, a more economical alternative foundation system was essential, and the alternative of a shaft bearing pile, a precast concrete pile, was proposed for Cai Mep Container Port. To reduce settlements, a soil improvement scheme was imposed, consisting of wick drains installed through the clay to the sand and placing an up to 8 m thick surcharge over the area. After removal of the surcharge, piled-raft foundations were constructed for the Port building, incorporating 400 mm square, precast concrete piles, which were driven to depths of 18 m. Settlement monitoring showed that the area and the piles continued to settle after the removal of the surcharge, indicating that consolidation settlement had not been completed despite the about 18 months long surcharge period. It became clear that the long-term settlements, primarily due to downdrag, would exceed the limit of maximum 400 mm over a 20-year period. In order to remedy the situation, the piles were lengthened to a total length of 44 m to ensure that the neutral plane was located in the sand, where no long-term settlement would occur. The problem and its solution were analyzed by means of the Unified Design Method. The remedial solution added about US$2 million to the project and caused a 12-month delay

Ground Vibrations Induced by Impact Pile Driving

The importance of vibration problems induced by pile driving is addressed and guidelines for establishing limiting vibration levels with respect to buildings with different foundation conditions are presented. Basic concepts of pile dynamics and stress-wave measurements, which were developed for the determination of driving resistance and bearing capacity of impact-driven piles, provide important information about ground vibration induced by pile penetration. Dynamic hammer properties and geometry as well as the driving process are important for ground vibration emission from the pile. It is shown that the energy-based, empirical approach, which is still widely used by practicing engineers, is too crude for reliable analysis of ground vibrations and can even be misleading. The main limitations of the energy approach are the assumption that driving energy governs ground vibrations, the omission of geotechnical conditions and soil resistance, and the uncertainty with regard to input values. Three types of ground waves are considered when analyzing pile driving: spherical waves emitted from the pile toe, cylindrical waves propagating laterally from the pile shaft, and surface waves, which are generated by wave refraction at the ground surface at a critical distance from the pile. These three wave types depend on the velocity-dependent soil resistance at the pile-soil interface. The most important factor for analyzing ground vibrations is the impedance of each system component, i.e., the pile hammer, the pile, and the soil along the shaft and at the pile toe. Guidance based on geotechnical conditions is given as to the selection of appropriate impedance values for different soil types. A theoretical concept is presented, based on a simplified model that considers the strain-softening effect on wave velocity in the soil, making it possible to calculate the attenuation of spherical and surface waves and of cylindrical waves generated at the pile toe and the pile shaft, respectively. The concept is applied to define k-values, which have been used in empirically developed models and correlated to type of wave and soil properties. An important aspect of the proposed prediction model is the introduction of vibration transmission efficacy, a factor which limits the amount of vibration force that can be transmitted along the pile-soil interface (toe and shaft). Results from detailed vibration measurements are compared to values calculated from the proposed model. The agreement is very good and suggests that the new model captures the important aspects of ground vibration during penetration of the pile into different soil layers. Finally, based on the presented model, factors influencing the emission of ground vibrations during impact pile driving are discussed

Failure of Embankment on Soil-Cement Columns for Thi Vai Port, Vietnam

The Thi Vai Container Port is constructed on reclaimed ground along the Thi Vai River in the Mekong delta approximately 90 km southeast of Ho Chi Minh City, Vietnam. The soil profile consists of an about 15 to 23 m thick deposit of soft, normally consolidated, highly compressible clay deposited on dense to compact sand. A soil improvement scheme was instigated aiming to reduce long-term settlement after construction of the facilities and improve the stability of the river bank. The scheme combined wick drains and, along the river bank, soil cement columns and toe revetments. The wick drains were installed at a spacing of about 1.5 m and a staged surcharge was placed to a maximum height of 6 through 6.6 m to bring about the consolidation of the clay. After a surcharge height of 4.7 m had been in place for about three months and the measured settlement was about 1.2 m, a slope failure occurred along about 200 m length of the riverbank. An investigation indicated that the three-month consolidation period had not increased clay undrained shear strength as anticipated and that the slope failure had broken the soil cement columns at about 11 m depth below the original ground surface. Costs to remedy the collapsed and damaged area amounted to about US$10 million. The paper presents the background information, soil failure details, results of bank stability analyses, and the solution chosen for the remedial construction

Effective stress analysis and set-up for shaft capacity of piles in clay

ABSTRACT A case history of repeated dynamic and static loading tests in Alberta on two pipe piles during dissipation of driving-induced pore pressures is presented together with three reanalyzed published case histories involving similar records. The four case histories demonstrate that, for each case, the same effective-stress proportionality coefficients, beta-coefficients, fit the capacities at different degrees of dissipation of excess pore pressures. For two of the test sites, the beta-coefficients back-calculated from the tests differed considerable from the values determined from the soil plasticity relation, while for two, the agreement is good. For one case, the backcalculated shaft resistance agreed well with the values of vane shear strength, while a less good agreement was found for the other tests. Neither case showed good agreement was found for methods combining undrained shear strength and effective overburden stress. Capacity calculations for two cases employing methods based on CPT soundings gave excellent agreement with one test and a poor agreement with the other. The increase of capacity due to aging after dissipation of excess pore pressures did not agree with cited recommendation for calculations of aging effect

Discussion of "Comparison of Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications regarding pile design subject to negative skin friction"

Discussions do not have abstractThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Observations and analysis of wide piled foundations

Available case histories on observations on full-scale piled rafts show that the settlement response to applied load can be modeled as that for an equivalent pier due to compression of the piles and the soil matrix plus that of an equivalent raft for compression of soil layers below the pile toe level. Interior piles engage the soil from the pile toe level upward in contrast to a single pile, which engages it from the ground downward. Piles and soil, combined as a pier, have strain compatibility, which requirement determines the distribution of load between the piles, the contact stress, and the load-transfer movement of the piles. The response between the interior and perimeter piles differ. Particularly so in non-subsiding and subsiding environment, because perimeter piles can be subjected to downdrag and drag forces, while neither downdrag nor drag force will affect the interior piles. In non-subsiding environment, it is advantageous to make perimeter piles shorter, while in subsiding environment perimeter piles best be longer. The load distribution across the raft is also governed by the degree of rigidity of the raft and by the difference in dishing at the pile toe level and in the dishing of the actual raft.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Negative skin friction on long piles driven in clay

(I) Results of a full scale investigation on instrumented piles; (II) General views and design recommendationI. Results of a full scale investigation on instrumented piles. II. General views and design recommendations.</p