GEOGUIDE 1 GUIDE TO RETAINING WALL ... - HKU Libraries

47tloading tests, pile tests and pumping tests, give E s values ranging from 0.2N to 2N MN/m 2(Whiteside, 1986). These correlations are comparable to the range of results for sands givenby Yoshida & Yoshinaka (1972), Parry (1978) and Burland & Burbidge (1985), The widerange of Eg' values is due to the different influence of the individual factors given in Section5.6. 1 in the various methods used to derive the values. For large retaining walls, field plateloading tests may be carried out to obtain Eg 1 values suitable for estimating the deformationsof retaining walls. However, the factors mentioned in Section 5.6.1 and the problemsassociated with plate loading tests, e.g. softening of the ground, should be considered wheninterpreting results and selecting design parameters.The one-dimensional or constrained modulus E 0 ', which is relevant to the case of onedimensionalcompression, is often sufficient for estimating settlement. E 0 is related to Eg 1fand j> ! s , the Poisson f s ratio in terms of effective stress, by the following equation :ES s '(lV- ? s ')S '° ~ (1 + „.•)(! - 20 ..........- »For values of *>§' in the range 0.1 to 0.3, E 0 ' varies between LllEs' and L35E S ', It shouldfbe noted that, by definition, E 0 = l/m v , where m v is the coefficient of volume change ofthe soil. Values of rn v over the relevant stress range can be obtained from oedometer testsor from the consolidation stage of triaxial compression tests. However, experience indicatesthat values derived from conventional triaxial compression tests often overestimate thecompressibility of Hong Kong granitic saprolite, and that values based on correlation withSPT ! N' values can give better predictions of overall field performance in such soils.For cohesive soils of relatively low permeability, it is necessary to estimate immediate(i.e. short-term) as well as long-term deformations. In assessing immediate deformations,'undrained 1 parameters in terms of total stress should be used. The Young's moduluscorresponding to ! undrained ! loading, EQ, may be calculated from E$* and *> u> the Poisson.'sratio corresponding to 'undrained* loading, using the following equation :>The value of *> u for a saturated clay can be taken as 0.5. For values of j> s ' in the range 0.1to 0.3, EU varies between IA5E S * and 1.36Es'.The value of Young f s modulus for unloading and reloading is usually much higherthan that for virgin loading. For preliminary design, values between 3 and 4 times theYoung's modulus for virgin loading are appropriate for the stress range below theprecompression pressure.5.6.3 Deformation Parameters for the Winkler Model(1) General The r beam on elastic foundation 1 or 'subgrade reaction 1 approach isoften used for analysing the internal forces and deformations of a cantilevered retaining waitIn this approach, the wall is represented by a vertical elastic beam and the soil mass ismodelled as a Winkler medium, for which displacement, y, is proportional to contact