Geotechnical Behavior of Pliocene Sedimentary Rocks Exposed along Qena-Safaga Road at Qena region, Egypt

Abstract

Geotechnical properties of Pliocene sedimentary rocks (Durri Formation) exposed along Qena-Safaga road were investigated to evaluate their geotechnical behaviour. The purpose of this research was to interpret a real reason of cracks occurring in the asphalt layer and in the area around the road and to suggest the suitable treatment of theses cracks. Durri Formation lies under the asphalt layer as sub-grade and exposed along the road at the study area. Mineralogical analysis of the studied samples showed that the Pliocene sedimentary rocks were mainly composed of calcite and clay minerals. Petrographical investigation showed that the studied Pliocene sedimentary rocks of Durri Formation at the studied area were mainly composed of five sedimentary microfacieses including mudstone, marlstone, marly, dolomitic and detrital limestone. Unconfined compressive strength of the studied sedimentary microfacieses was ranging from 155.92 to 291.92kg/cm<SUP>2</SUP>. Mudstone and detrital limestone microfacieses had the lowest values (155.92 to 197.50kg/cm<SUP>2</SUP>); in contrast, marlstone, marly limestone and dolomitic limestone microfacieses had the highest values (218.29 to 291.92kg/cm<SUP>2</SUP>). Swelling pressure value of the mudstone microfacies was 6.50kg/cm<SUP>2</SUP> and the swelling pressure of the marly limestone microfacieses was ranging from 0.44 to 2.10kg/cm<SUP>2</SUP>. Marlstone microfacies had the highest swelling pressure value (16.00kg/cm<SUP>2</SUP>). In contrast, dolomitic and detrital limestone microfacieses had not swelling pressure. Retained percent of the slaking durability test of the studied sedimentary microfacieses was ranging from 88.70 to 94.60% having medium to high durability according to slake durability classification of Gamble, except one high expansive marlstone microfacies had low retained percent (58.00%) and was described as low durability microfacies. Expansive sedimentary rock microfacieses of Durri Formation including mudstone, marlstone and marly limestone microfacieses which represent the sub-grade of the road were swollen due to water coming from the damaged old water pipe that runs parallel to the road and that led to a heave of both the road and the damaged old water pipe. The heave of the old water pipe led to an increase of the damage and the amount of the water coming from this pipe. In addition, drying the saturated Pliocene sedimentary microfacieses due to solar radiation led to a formation of large scale mud cracks having triple junction, polygonal and randomly oriented forms. These cracks occurs on the asphalt layer and in the area around the road at the study area. Grouting of the cracks using cement and chemical stabilization of the expansive sub-grade sedimentary microfacies utilizing lime were suggested to treat these cracks and to reduce the swelling pressure respectively. In addition, monitoring system of the cracks using total station was suggested to evaluate the displacement of these cracks and to determine the relationship between cracks origin and recent tectonic movement at the study area.