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在高混凝土坝迎水面下部的基础内,无疑会形成拉应力区,规范CHNП—Ⅱ—54—77指出了“拉力区的基础连续性遭到破坏的可能性。”布拉茨克坝发现了因拉应力而引起基础的松驰,主要原因是柱状浇筑的坝,其纵缝灌浆效果不好,使坝断面不完全成整体。这已为静水荷载作用下,在水平截面的纵缝观测孔和受力分布特性所证实。在对三个坝的研究后发现,基础松驰后的原型观测资料是不同的:当库水位尚未开始消落时,布拉茨克坝扬压力骤然增加;在基洛夫斯克坝,当上游水位相当于正常高水位的60％时,迎水面下部的接触缝就开始开裂,其开度随上游水位的升高而增大,与此同时,坝基测压管水头和渗水量也跟着增加。在乌斯基——伊里姆斯克坝,即使接触缝开裂的坝段,它的扬压力和接触缝没有开裂的那些坝段的扬压力一样小。由此可见,在乌斯基—伊里姆斯克坝迎水面下部存在由渗流产生附加的卸荷。
Tensile stress zones are undoubtedly formed within the foundation of the lower concrete facing dam of a high concrete dam and the code CHNП-II-54-77 states “the possibility of destruction of the basic continuity of the tension zone.” The Bratsk Dam Due to tensile stress caused by the relaxation of the foundation, the main reason is that the columnar pouring dam, the longitudinal grouting effect is not good, so that the dam section is not completely integrated. This has been confirmed by the hydrostatic load in the horizontal section of the longitudinal slit observation hole and stress distribution characteristics. After studying the three dams, the prototype observation data after the foundation relaxation are different: when the water level in the reservoir has not started to decline, the pressure in the Bratsk dam suddenly increases; in the Kirovsky dam, when the upstream When the water level is equivalent to 60% of the normal high water level, the contact seam at the lower part of the water level surface begins to crack, and its opening degree increases with the rise of the upstream water level. At the same time, the head and water seepage amount of the piezometer in dam foundation also increase. At the Ust-Iliomsk dam, the thrust of those sections where the uplift pressure is the same as those at which the contact seams are not cracked is as small as that even if it contacts the cracked section of the crack. Thus it can be seen that there is additional unloading by seepage in the water-front lower part of Uxki-Ilimsik dam.