Effect of soaking time on the geotechnical behavior for different types of sedimentary rocks in Egypt

Abstract

ABSTRACT Weathering problems of weak sedimentary rocks, especially when subjected to water immersion, are considered one of the serious geotechnical engineering issues. Examples of rock water submersion include foundations subject to seepage, regular irrigation, residence daily activities, service water, frequent plant watering, an increase in groundwater level and heavy rain, in addition to numerous urban and rural water use consequences; hence, it is necessary to quantify the effect of water on the physical and mechanical characteristics of sedimentary rocks. The objective of this study is to assess, evaluate and estimate the strength and stiffness of deterioration of sedimentary rocks in Egypt subject to freshwater soaking in three states (natural/presoaking state, after 48 h and after 30 days of soaking). An extensive laboratory testing program including slake durability, uniaxial compression and point load tests was conducted in the three states on sandstone and limestone specimens collected from Galala, Attaka-Suez Governorate, Egypt. The influence of water immersion on the physical and mechanical characteristics such as rounding, stress–strain envelope, strength and stiffness was studied. The results showed a reduction of up to 87% and 93% in the uniaxial compressive strength and elastic modulus, respectively, post 30 days of freshwater soaking. The limestone showed more resistance to deterioration compared to the sandstone. The stiffness and strength of sedimentary rocks decrease with long contact with water. This paper results provide guidance when assessing, planning and preliminarily evaluating similar rock formation/s considered as a candidate for engineering projects.