本科毕业设计外文翻译(编辑修改稿)

本科毕业设计外文翻译(编辑修改稿)内容摘要：

ing that the degree of wall displacement or flexibility required to reduce retained earth pressures to their fully active values in cohesionless materials is only of the order of a rotation of 103 radians. In each of these cases, mobilized soil strengths will increase as deformations continue, so the unfavorable earth pressure conditions dill not persist as collapse approaches. The design earth pressures are derived from design soil strengths using the usual methods of plastic analysis, with earth pressure coefficients (see ) given in this code of practice being based on Keriselamp。 Absi(1990). The same design earth pressures are used in the default condition for the design of structural. sections, see . Design method Equilibrium calculations In order to determine the geometry of the retaining wall, for exampal the depth of peration of an embedded wall (see ), equilibrium calculations should be carried out for care formulated design situations. The design fully calculations relate to a freebody diagram of forces and stresses for the whole retaining wall. The design calculations should demonstrate that there is global equilibrium of vertical and horizontal forces, and of moments. Separate calculations should be made for different design situations. The structural geometry of the retaining wall and the equilibrium calculations should be determined from the design earth pressures derived from the design soil strength using the appropriate earth pressure coefficients. Design earth pressures will lead to active and passive pressure diagrams of the type shown in figure 4. The earth pressure distribution should be checked for global equilibrium of the structure. Horizontal forces equilibrium and moment equilibrium will give the prop force in figure 4a and the location of the point of reversed stress conditions near the toe in figure 4b. Vertical forces equilibrium should also be checked. Design situations General The specification of design situations should include the disposition and classification of the various zones of soil and rock and the elements of construction which could be involved in a limit state event. The specification of design situations should follow a consideration of all uncertainties and the risk factors involved, including the following: a) the loads and their binations, . surcharge and%or external loads on the active or retained side of the wall。 b) the geometry of the structure, and the neighbouring soil bodies, representing the worst credible conditions, for example overexcavation during or after construction。 c) the material characteristics of the structure, . following corrosion。 d) effects due to the environment within which the design is set, such as: ground water levels, including their variations due to the effects of dewatering possible flooding or failure of any drainage system。 scour, erosion and excavation, leading to changes in the geometry of the ground surface。 chemical corrosion。 weathering。 freezing。 the presence of gases emerging from the ground。 other effects of time and environment on the strength and other properties of materials。 e) earthquakes。 f) subsidence due to mining or other causes。 g) the tolerance of the structure to deformations。 h) the effect of the new structure on existing structures or services and the effect of existing structures or services on the new structure。 i) for structures resting on or near rock, the consideration of: interbedded hard and soft strata。 faults, joints and fissures。 solution cavities such as swallow holes or fissures, filled with soft material, and continuing solution processes. Minimum surcharge and minimum unplanned excavation In checking the stable equilibrium and soil deformation all walls should be designed for a minimum design surcharge loading of 10 kN/m2 and a minimum depth of excavation in front of the wall, which should be: a)not less than m。 and b)not less than10% of the total height retained for cantilever walls, or the height retained lowest support level for propped or anchored walls. These minimum values should be reviewed for each design and more adverse values adopted in particularly critical or uncertain circumstances. The requirement for an additional or unplanned excavation as a design criterion is to provide for unforeseen and accidental events. Foreseeable excavations suet as service or drainage trenches in front of a retaining wall, which may be required at some stage in the life of the structure, should be treated as a planned excavation. Actual excavation beyond the planned depth is outside the design considerations of this code. Water pressure regime The water pressure regime used in the design should be the most onerous that is considered to be reasonably possible. Calculations based on total and effective stress parameters The changes in loading associated with the construction of a retaining wall may result in changes in the strength of the ground in the vicinity of the wall. ifhere the mass permeability of the ground is low these changes of strength take place over some time and therefore the design should consider conditions in both the short and longterm. Which condition will be critical depends on whether the changes in load applied to the soil mass cause an increase or decrease in soil strength. The longterm condition is likely to be critical where the soil mass undergoes a reduction in load as a result of excavation, such as adjacent to a cantilever wall. Conversely where the soil mass is subject to a increase in loading, such as beneath the foundation of a gravity or reinforced stem wall at ground level, the shortterm condition is likely to be critical for stability. When considering。