Elastoplastic Analysis On Hole Expansion Issue Of Pile Based On The Theory Of Unified Strength

Construction methods like compaction pile, static pile, sinking tubular pile, which has soil compaction effects, are the most common and most effective conventional methods of dealing with the foundation in domestic and international engineering. These construction technologies can improve soil; forming a composite foundation to enhance the foundation bearing capacity. Engineering principles involved in belong to hole expansion issue of pile, therefore, in the process of reaming, theoretical research on stress and displacement field of soil around pile hole has important meaning and engineering value for applications.At present, most pile reaming study limited to research on its engineering technology and different ways of dealing with the quality, but seldom involved in stress changes around the hole pile soil and soil compaction mechanism in the process of reaming. At the same time, pile reaming process, the soil change around the hole of the stress field and the corresponding changes in the plastic deformation of theoretical research are imperfect. Tresca criterion, Mohr-Coulomb criterion were used in the process of theoretical derivation in the past. None of considering the influence of the middle principal stress and soil SD effects, which reflects on the calculation results inconsistent with the actual situation. Therefore, we adopt unified strength theory and hole expansion theory in elastic-plastic analysis of stress and displacement field around the soil.In the clay, if we suppose the stress-strain relationship to be an ideal elasto-plastic model, and that the soil in plastic materials subject to the unified yield criterion, small strain theory is adopted in the elasto-plastic areas. New unified strength theory is adopted respectively in theoretical derivation of problems pile and the pile reaming pile groups. The plane stress and plane strain field in the state of single pile and pile groups, systematically showing a series of new analytical formula, which describe behavior of pile reaming. The process consider the effect of soil materials SD (different tension and compression properties) and the middle principal stress effect, and under the effect of the above two parameters identification, formula could degenerate into a different, new one describing the pile reaming. In order to compare with the analysis of the past, the paper shows Tresca series which describe soil pile reaming in clay. And at the same time the clay in the unified strength parameters of impact analysis. Above theoretical results can be effectively applied to engineering problems in the field of theoretical analysis and design of soil reaming in clay.In the non-clay, we suppose the stress-strain relationship of soil around the pile to be ideal elasto-plastic model, and that the soil materials subject to the unified yield criteria, stress analysis in elastic and plastic zone adopts respectively small strain theory and large strain theory. With the introduction of dilatancy angle to large strain of the plastic ring and the use of infinite series iterative calculation, dilatancy soil relations of expansion of the large strain hole were obtained. When plastic ring come forth in non-clay, relationship between stress and strain can be derived from non-associated flow rule. The paper shows a series of new analytical formula in pile reaming through using new unified strength theory to give theoretical derivation of plane stress and plane strain field under the situations of single pile and pile groups in non-clay pile reaming, and the analytical formula under single pile is special case under situation of pile groups. The effect of soil materials SD (different tension and compression properties), the middle principal stress effect, the unified strength of tension and compression ratioαand the middle principal stress factor b which affect the determination of Analytic are considered in the process. Formula may degenerate into a different, new one to describe non-clay pile reaming. In order to give a contrast of the analysis and the past one, the paper shows Mohr-Coulomb series which describe clay pile reaming and at the same time impact analysis of parameter in the unified strength of the non-clay. Above theoretical results can be effectively applied to engineering problems in the field of theoretical analysis and design of non-clay pile reaming.This paper shows parameters impact analysis for pile reaming elasto-plastic theory, discuss the relationship between hole expansion force and hole expanding ratio of limited border of group piles reaming and impact of factors such as initial radius of the pile-border, the initial stress, shear modulus of the soil, soil dilatancy angle, internal friction angle on the pile reaming. For clay, the theoretic data have good consistency and similarity with experimental data of Hughes based on the premise of same parameters. Similarly, for non-clay, this theory is quite close to the experimental data of Hughes under the premise of same soil parameters, in particular under the circumstances of single pile (i.e. unlimited border). The theoretical and experimental values of the degree fit better, and error of the two is within 5 %. At the same time, the above analysis of the impact of soil parameters obtained parameters impact rules of deformation of soil in the process of pile reaming. These rules are great convenient to analysis on pile reaming problem for clay and non-clay.This paper shows impact analysis on limit reaming in the process of pile reaming from five factors, such as internal friction angle, dilatancy angle, Poisson's ratio, shear modulus of the soil and pile-border, obtaining general rale of soil parameter impact. Limit reaming of the internal friction angle is proportional to frictional angle; Soil dilatancy angle has little impact on the ultimate hole expansion force; Poisson's ratio has little impact on ultimate hole expansion force; Clay and sand within reasonable limits increased shear modulus and change of the limit reaming is less than twice. The larger Border- Diameter ratio is, the greater of ultimate hole expansion force will be, but ultimate hole expansion force ratio minish with the increase in border of pile hole reaming. The smaller the modulus of elasticity and the greater the impact on the border of pile hole reaming, the more obvious ultimate hole expansion force is. Here are the general rales of ultimate hole expansion force affected by the soil parameters and it can provide better guidance for engineering design of pile reaming aspects.