Properties of the London Clay at the Ashford Common Shaft: in-Situ and Undrained Strength Tests

Abstract

Summary During the construction of the Ashford Common shaft by the Metropolitan Water Board undisturbed block specimens were obtained from six levels at depths varying from 30 to 140 ft in the London Clay. At the same levels a series of plate loading and penetrometer tests were carried out in the shaft. In a special boring alongside the shaft a series of Dutch cone penetrometer tests were made and some special samples taken. The Metropolitan Water Board also made available the results on conventional borehole samples from eight borings in the neighbourhood of the shaft. In this Paper the results of an extensive series of quick undrained compression tests on the block specimens are presented and the undrained shear strength–depth relationships obtained from the several types of laboratory and in-situ tests compared. These vary considerably and the differences are discussed in terms of the fissured nature of the clay and the effects of excavation. The penetrometer tests cannot bc evaluated satisfactorily. Au cours de la construction du puits du Communal d'Ashford par le Service des Eaux Métropolitain, on a prélevé une série de blocs-échantillons intacts à six niveaux de profondeurs variant de 10 à 50 mètres dans l'argile londonienne. On a fait une série d'essais de charge sur plaque et au pénétromètre dans le puits aux mêmes niveaux. Dans un sondage spécial près du puits on a fait une série d'essais au pénétromètre à cône hollandais et on a prélevé des échantillons spéciaux. Le Service des Eaux Métropolitain a communiqué aussi les résultats obtenus sur des échantillons de trou de sondage conventionnel de huit sondages dans le voisinage du puits. Dans cet article on présente les résultats d'une vaste série déssais de compression à teneur en eau constante sur des blocs-échantillons et on compare les rapports de résistance au cisaillemcnt à teneur en eau constante avec le profondeur, obtenus avec les types multiples d'essais en laboratoire et in situ. Ces derniers varient considérablement et les différences y sont discutées d'aprés la nature fissurée de l'argile et les effets d'excavation. On n'a pas pu évaluer les essais au pénétromètre d'une manière satisfaisante.

The laboratory measurement and interpretation of the small-strain stiffness of stiff clays

“…Similar considerations apply to the measurement of stiffness in undrained triaxial extension tests. It should also be recalled that the undrained horizontal stiffness of London Clay is significantly higher than the undrained vertical stiffness at small strains ( and at relatively large strains (Ward et al (1965) and Bishop et al (1965)). …”

The analytical method in soil mechanics

“…There was a good deal of evidence (for London Clay see Skempton and Henkel, 1957;Ward, et al, 1959Ward, et al, , 1965 Two extreme cases can be identified (a) x=0 (b) E(0) =o. The first of these is the ctassical case and would provide a useful check of the general analysis.…”

“…Special features at the various sites can explain some of the variations in Table l-for example, the high degree of fissuring observed in samples from site G-and these points have been discussed in detail by the authors, but the overall picture is quite clear. Data from more than three hundred undrained compression tests on specimens cut from block samples of London Clay obtained from various depths at Ashford Common were published subsequently (Ward et al, 1965) and this has been used in Table 2. Undrained tests were conducted on samples cut vertically, horizontally and inclined at 45" and these are referred to by the symbols V, H and D. The ratio of horizontal to vertical modulus is some 20% higher on average here and at depths of 66 and 91 ft the ratio exceeds 2.…”

Fundamental solutions for an inhomogeneous cross-anisotropic material due to horizontal and vertical plane strain line loads

“…He concluded that the ratio E/E for clays ranges from 0.6 to 4, and was as low as 0.2 for sands. However, for the heavily overconsolidated London clay, the range of E/E was 1.35-2.37, and that of the ratio G /E was 0.23-0.44 [Ward et al 1965;Gibson 1974;Lee and Rowe 1989;Tarn and Lu 1991;Wang et al 2008]. The ratio ν/ν is hypothetically assumed to be within the range 0.75-1.5 in this study.…”