Analysis of Drilling in Cobble Layer and Direct Static Sounding in Pre-guide Hole

To get the physical and mechanical properties of cobble and boulder, you should first find out the compactness, grain size, distribution patterns, contents, and the fillings content. Now, lower construction efficiency, great labour intensity and high cost are the main problems in drilling. Meanwhile, there is a limitation that using dynamic sounding to judge the density of cobble, because it is much higher when drilling the surface of cobble, and lower when drilling the fracture of cobble. Considered with 《Technical specification for engineering geological prospecting and sampling of constructions》JGJ/T 87-2012 attached table G.0.6, the acquired compactness will be more objective. Static sounding generally cannot cross tight gravels, so how to get the static sounding data below them is a difficult problem in our work. Based on several different geotechnical engineering exploration practices, this paper discussed the solutions for the above mentioned problems.