Design Theory Of Retaining Structure With Pile Wall For Circular Deep Excavation In Pebble Layer

In recent decades, with the construction and development of multi-layer basement of high-rise building, underground railway, station, underground municipal facilities, industrial and military infrastructure and so on, the deep excavation engineering is gradually increasing. The forms of the plane layout are more and more diversified, such as rectangular, circular and other irregular forms.As a kind of closing arch ring structure, circular deep excavation presents the main characteristic of bearing circular pressure. At the same time, due to the influence of the soil arching effect, the soil pressure acting on the retaining and protection structure for circular excavation is small compared with the excavations with other forms of plane layout. This is beneficial to the structural stress and the control of deformation. So far, the deep excavation projects by literature review and reporting publicly most lie in coastal soft soil region in the retaining form of underground continuous wall. For the sand-pebble layer (whose characteristic is very different from the coastal soft soil layer), there are not research results of the retaining and protection structure with soldier pile wall for deep circular excavation by literature review and reporting publicly so far. The main reason lies in two aspects:one is the lack of design theory of the retaining and protection structure with soldier pile wall for deep circular excavation in the sand-pebble layer; the other is the lack of construction experience of the retaining and protection structure with soldier pile wall for deep circular excavation in the sand-pebble layer. Those result in very carefully and less using when choosing the retaining and protection structure with soldier pile wall for deep circular excavation. And even the application according to the general mechanical model which have not fully considered the space effect of the deep circular excavation and the pile-soil interaction. This calculation pattern may lead to conservative design, and even have conduction but failed to form research result thorough intensive research. Therefore, the study of design theory of the retaining and protection structure with soldier pile wall for deep circular excavation in the sand-pebble layer has important theoretical value and practical significance.This research project make a study on the theory of computation of soil pressure acting on the retaining and protection structure with soldier pile wall for deep circular excavation in the sand-pebble layer, internal force and theory of deformation calculation for retaining and protection structure with soldier pile wall. The practical calculation method is put forward, at the same time, the common parameters and the influencing factors of the retaining and protection structure with soldier pile wall are analyzed and discussed by the method of elastic theory of thick-walled cylinder, three-dimensional numerical simulation, laboratory model test, assess of engineering example and so on. The characteristics of sand-pebble layer, the space effect of deep circular excavation and the characteristics of pile-soil interaction basis on widely collecting relevant research data at home and abroad are studied.The main results, conclusions and suggestions of this scientific research project are as follows:1. The calculation formula of soil pressure acting on retaining and protection structure with soldier pile wall for deep circular excavation is set up by elastic theory of thick-walled cylinder. The diameter of excavation, pile diameter, flexural stiffness of pile, pile diameter, weight of soil, elastic modulus, Poisson’s ratio, internal friction angle, coefficient of earth pressure at rest and other parameters are included in this formula.2. The overall distribution of soil pressure of retaining and protection structure with soldier pile wall for deep circular excavation is nonlinear under different depth of excavation. It is approximately linear in different soil layer so it can be dealt with piecewise linearity. The soil pressure behind piles is between the active soil pressure and the static soil pressure, and it is more close to the Rankin active soil pressure. With the increase of excavation depth, the soil pressure along pile has the characteristic of decreasing, but the resultant force of behind piles has a tendency of gradual increase in soil pressure, especially obviously within the lower range of 1/3 to 2/3 in excavation.3. The model of statically indeterminate multi-span continuous beam for pile which is fixed at the bottom of pile, has the sliding support at the top of pile and has the fixed hinge bearing in the middle of pile can be adopted in analysis of internal force and deformation above the excavation surface of pile at any excavation depth. At the same time, the method of beam on elastic foundation is adopted in calculating internal force and deformation of pile below the excavation surface, and the internal force and deformation coordination should be pay attention in two compartments. The theory and formula of calculation for internal force and deformation in the retaining and protection structure with soldier pile wall have been established.4. The capping beam and waling of the retaining and protection structure present the main characteristic of bearing circular pressure in which the share force and the bending moment is small. The dimension of capping beam is mainly determined according to the detailing requirement. The waling at the bottom has the maximal axial force.5. The rigidity and interval of waling have a large influence on the internal force and deformation of the retaining and protection structure with soldier pile wall. It may be in good condition of force in retaining and protection structure with soldier pile if adopting the support of waling with big stiffness in the deep circular excavation as early as possible.6. The lateral displacement of supporting pile is large in the middle and small on both ends of the pile. The maximum lateral displacement is generally appear at the position of 1/2-2/3 of the excavation depth.7. As the diameter of excavation is greater, the space effect of the excavation is less obvious. It is suggested that the diameter range is 30 to 40 meters fully considering the space effect of the retaining and protection structure with soldier pile wall for deep circular excavation. If it exceeds the diameter range, the space effect should be reduced.