【正文】 , for stability of slopes, are described in BS 6031 and in BS 8081. Where the mode of failure involves a bearing capacity failure, the calculations should establish an effective width of foundation. The bearing pressures as determined from should not exceed the ultimate bearing capacity in accordance with BS 8004. Where the mode of failure is by translational movement, with passive resistance excluded, stable equilibrium should be achieved using the design shear strength of the soil in contact with the base of the earth retaining structure. Where the mode of failure involves a rotational or translational movement, the stable equilibrium of the earth retaining structure depends on the mobilization of shear stresses within the soil. The full mobilization of the soil shear strength gives rise to limiting active and passive thrusts. These limiting thrusts act in concert on the structure only at the point of collapse, . ultimate limit state. Serviceability limit states The following serviceability limit states should be considered: a) substantial deformation of the structure。 by the method given in and . The design earth pressures used for serviceability limit state calculations will differ from those used for ultimate limit state calculations only w here structures are to be subjected to differing design values of external loads (generally surcharge and live loads) for the ultimate limit state and for the serviceability limit state. Limit states and patibility of deformations The deformation of an earth retaining structure is important because it has a direct effect upon the forces on the structure, the forces from the retained soil and the forces which result when the structure moves against the soil. The structural forces and bending moments due to earth pressures reduce as deformation of the structure increases. The maximum earth pressures on a retaining structure occur during working conditions and the necessary equilibrium calculations (see ) are based on the assumption that earth pressures greater than fully active pressure (see ) and less than fully passive will act on the retaining structure during service. As ultimate limit state with respect to soil pressures is approached, with sufficient deformation of the structure, the active earth pressure (see ) in the retained soil reduces to the fully active pressure and the passive resistance (see ) tends to increase to the full available passive resistance (see ). The patibility of deformation of the structure and the corresponding earth pressures is important where the form of structure, for example a propped cantilever wall, prevents the occurrence of fully active pressure at the prop. It is also particularly important where the structure behaves as a brittle material and loses strength as deformation increases, such as an unreinforced mass gravity structure or where the soil is liable to strain softening as deformation increases. Design values of parameters These are applicable at the specified limit states in the specified design situations. All elements of safety and uncertainty should be incorporated into the design values. The selection of design values for soil parameters should take account of: a) the possibility of unfavorable variations in the values of the parameters。 c) the quality of workmanship and level of control specified for the construction. Applied loads The design value for the density of fill materials, should be a pessimistic or unfavorable assessment of actual density. For surcharges and live loadings different values may be appropriate for the differing conditions of serviceability and ultimate limit states and for different load binations. The intention of this code of practice is to determine those earth pressures which will not be exceeded in a limit state, if external loads are correctly predicted. External loads, such as structural dead loads or vehicle surcharge loads may be specified in other codes as nominal or characteristic values. Some of the structural codes, with which this code interfaces, specify different load factors to be applied for serviceability or ultimate limit state the checks and for different load binations, See .Design values of loads, derived by factoring or otherwise, are intended, here, to be here most pessimistic or unfavorable loads which should he used in the calculations for the structure. Similarly, when external loads act on the active or retained side of the wall these same external loads should be derived in the same way. The soil is then treated as forming part of the whole structural system. Design soil strength (see ) Assessment of the design values depends on the required or anticipated life of the structure, but account should be taken also of the shortterm conditions which apply during and immediately following the period of construction. Single design values of soil strength should be obtained from a consideration of the representative values for peak and ultimate strength. The value so selected will satisfy, simultaneously, the considerations of ultimate and serviceability limit states. The design value should be the lower of: a) that value of soil strength, on the stressstrain relation leading to peak strength,which is mobilized at soil strains acceptable for serviceability. This can be expressed as the peak strength reduced by a mobilization factor M as given in or 。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 relat