The fill placement works on the foundation as overburden loading. This loading will compress the foundation and cause the decrease of permeability. Therefore, the authors actually measured the deformation of the foundation and the change of permeability due to fill placement at three damsites. The measured results indicate that the fill placement causes the compression of dam foundations and the decrease of permeability. Moreover, taking these results into consideration, the authors propose the effective designing of grouting for dam foundations, particularly weak rock foundations.
Le remblayage produit sur les fondations l'effet d'une charge due au poids des terres. Cette charge comprime les fondations et provoque une diminution de la permeabilite. En consequence, les anteurs ont meaure, sur le site de trois barrages, la deformation des fondations et la diminution de la permeabilite provoquees par le remblayage. Les resultats de ces mesures indiquent que le remblayage provoque la compression des fondations des barrages et la diminution de leur permeabilite. En tenant compte de ces resultats, les auteurs proposent, de plus, une conception efficate d'injection des fondations d'un barrage, plus particulierèment dans le cas de fondations à roches tendres.
Die Aufschuettung wirkt auf das Fundament als Abraum-Belastung. Diese Belastung drueckt das Fundament zusammen und bewirkt eine Verringerung der Durchlassigkeit. Daher haben die Autoren die Verformung des Fundaments und die Veranderung der Durchlassigkeit bei drei Dammen gemessen. Die Meβergebnisse zeigen, daβ die Aufschuettung das Zusammendruecken des Fundamentes und die Verringerung der Durchlassigkeit bewirkt. Weiterhin schlagen die Autoren unter Beruecksichtigung dieser Ergebnisse die wirksame Konstruktion von Auspressung von Dammfundamenten, insbesondere schwache Felsfundamente, vor.
Controlling seepage in the dam foundation is one of the most important and challenging parts of dam engineering. There are three basic methods for controlling seepage, i.e. reduction of seepage, drainage, and use of filters. As for rock foundations grouting is most frequently adopted among several seepage reduction methods. Foundation grouting at dams takes the form of curtain and blanket grouting. The curtain grouting is provided down to a comparatively deep depth at the foundation for the purpose of cutting off the under seepage. The blanket grouting is provided at a comparatively shallow depth to make the area more impermeable or to consolidate fractured or jointed rock. Recently, in Japan, most of the sites which have satisfactory geological conditions for the construction of dams have been already developed. Therefore, dams tend to be constructed on the sites which are not always satisfactory in terms of geological conditions. In selecting the type of dams, a fill dam is often chosen for the sites which are low in bearing capacity for concrete dams. Therefore, not a few damsites for the fill dams under construction and planning are composed of weak rocks such as soft, or weathered, or fractured rocks. Since the higher grouting pressures cause fracturing or lifting the surface of weak rock foundations, the allowable pressures should be kept low in weak rocks. Furthermore, these weak rocks often have fine joints or fissures which are not groutable by cement. Therefore, it is very difficult to reduce the permeability in weak rock foundations, particularly in shallow areas, by cement grouting. On the other hand, since weak rock foundations show large deformability, these foundations, especially shallow areas, are expected to deform due to the loading of fill placement. If the foundation rocks themselves are consolidated and the above-mentioned joints or fissures are closed, the permeability of foundations will decrease. The authors feel that investigations on the quantitative relationship between the compressive strain and the decrease of permeability are very useful for controlling seepage in dam foundations. From the above-mentioned viewpoint, the authors try to reveal the relationship between the compressive strain and the decrease of permeability due to fill placement in fill dams through the in-situ measurements at three dam sites. Moreover, taking these results into consideration, the authors propose the effective designing method of grouting for dam foundations, particularly weak rock foundations. Although a lot of researches on the permeability and the grouting of dam foundations have been already reported, there have been few systematic researches from the above-mentioned viewpoint. Installation of foundation galleries at the base of fill dams enabled to obtain in-situ data of consolidation effects on the permeability due to fill placement.
The measurements of the deformation and the change of permeability at dam foundations due to fill placement were conducted at three dam sites shown in Table 1.