As one of investigation for a foundation of Akashi Bridge, the writers attempted to measure the deformation characteristics of the Kobe Group, the tertiary sedimentary rock. Since the actual site for the foundation is deep in the sea, the site of a similar geological condition at a hill site was selected for a series of large scale loading test.
Several laboratory triaxial tests and field pressuremeter tests were performed to assess the strength and deformation characteristics. Field measurement of strain distribution below the loading plate was carried out by strain gauge type transducers installed in the ground. As it was known that the ground showed very complex geological structure with pre-boring exploration, detail observation was carried out by exploratory excavation at the test site.
The purpose of this paper is to study the strain distribution of multi-layered soft sedimentary rock mass in the plate loading test, and the numerical results compared with those of field measurments.
Numbers of boring were carried out to investigate the geological condition. A geological section at the site, together with modulus of deformation Esp obtained from pressuremeter, is given in Fig. 1. The site consists of very complex stratifed sandstone and mudstone.
As Kobe Group at the site is easily to cause slaking, the flattened surface with a thin layer of mortar, after the weathered surface layer was trimmed. A loading plate was placed on the flattened surface with a thin layer of cement paste at the bottom of further 0.5 m excavation. Two series of loading test were carried out with a set of 4 loading plates of 60 cm in diameter and 1 plate of 200 cm in diameter. Before the loading test, bore holes of 65 mm in diameter were drilled at the centers of the plates and at several other points to measure rock mass deformability with pressuremeter. Strain gauge type transducers were embeded at desired depths of the boreholes filled with cement material which were mixtures of gypsum and diatomaceous earth.
(Figure in full paper)
Some of the loading tests were already reported by Mori(1977), Akai(1979) and Takahashi(1981). This paper discusses mainly about the results of strain measurement in the ground. Strain distribution obtained from loading tests are ploted in Fig. 2. Results of A-1 series show unexpected distribution which show maximum strain at some depth, while those of A-2 series show decreasing with depth. Most plates of A-2 series were placed on mudstone and type of faiure in this series are likely as obtained in L-60 -21(Fig. 4). An example of load-strain relationship with depth is shown in Fig. 3, and it shows the maximum strain at 0.55 m deep from an initial loading and the results in Fig. 3 indicates much difference from one for an elastic homogeneous ground.
(Figure in full paper)
To check ground conditions, exploratory excavation was carried out at the test sites. Geological section, at the mentioned test sites in Fig. 2 were estimated based upon logs of exploratory trenches and are illustrated in Fig. 4.
