Soil Displacement And Pore Pressure By Pile Driving In Soft Clay With Structure Damage

Static piling is now widely used in civil engineering, especially in high building of soft clay foundation, because of its various advantages, such as its high quality, easy settlement, lower cost, and no pollution of noisy and slurry, etc. But it is displacement pile, and can cause disadvantageous effect on adjacent building if the proper techniques are not adopted. As the negative effect on around engineering environment is understood more and more, many researchers try to study the phenomena and solve the problem. However, results from their work are still not satisfied.Basing on those previous studies, the author makes the improvement by considerating the influence of soil structural strength on analyzing the soil displacement and pore water pressure by pile driving. Soft clay can be cemented naturally and behave special properties of mechanics, particularly the stress-strain relationship shows strain-softening after soil yielding. It is obvious that the results will be greatly different when analyzing the stress and displacement field and pore water pressure around pile by hardening rules and softening rules.Focus on the structural characteristics of clay, the author has studied the problem . Main original work in this thesis includes:Firstly, the mechanical characteristics of naturally cement clay are studied by comparing and analyzing the compressibility curve, coefficient of consolidation, distributing of pore water pressure (UU), and stress-strain relationship. Then the rules of the influence of structural strength of soft clay on mechanical properties are concluded.Secondly, take the phenomena of strain-softening after yielding as the un-reversible results of the disruption of microstrucrure in soil particles. According continuum damage mechanics and similitude breakdown manner between soil particles and metal particles, the structure damage evolution of structural clay are established. Under the hypothesis of anisotropic damage in clay, the elastic and plastic damage model are used to express stress-strain relationship of softening soil.Thirdly, predigest stress-strain curve to a lineal model, three line segments represent elastic period before yielding, softening period after yielding and plastic period with strain increase infinitely respectively. During the softening period, the stress decreased gradually while strain increased linearly, and obviously it is different from a stress-dropping strain -softening model. Using this lineal model, the effectcaused by different strain-softening rates on stress and displacement fields, pore water pressure, and development of the plastic zone of expansion of cylindrical cavity are analyzed.Finally, the stress and displacement field between two piles are also analyzed under the condition of two piles interactions. In addition, two examples of pile groups were discussed, including the shielding effect of first-pile, the stress concentration of pile groups, and the corresponding managements in engineering.It can be concluded that the structure of soft clay has influence on the stress and displacement field and the pore water pressure distribution around the pile. The structure damage of clay will decrease the stress around the pile, and the displacement under structure damaged was larger than undamaged condition. The structure increase the soil strength, and therefore make soil produce a higher pore water pressure.