In the past, engineering geology mainly focused on soil and hard rocks, with little attention paid specifically to weak/soft rocks, defined by a UCS below 25 MPa (ISRM in Int J Rock Mech Min 18:85-110, 1981). Weak rock is an intermediate, which is difficult to analyze, and requires application of both soil and rock mechanics principles. The Sherwood Sandstone Group (SSG) in Nottinghamshire (UK) is often characterized as weak rock, containing extremely weak members, which display a UCS between 0.6 and 1 MPa according to the definition from BS 5930:2015 (British Standards Institution 2015). Little research has been conducted on the locally extremely weak members of the Sherwood Sandstone Group, in particular the Nottingham Castle Sandstone Formation, and engineering projects within this unit can face major design challenges. This study aims at investigating the intact material, characterizing the SSG and analysing the stability of a slope in a quarry between two water-filled silt lagoons at the Two Oak Quarry, close to Mansfield. Laboratory testing, including UCS tests, triaxial tests, tensile tests and Slake Durability tests, is Keywords Geotechnical characterization Á Slope stability Á Quarry stability Á Weak rock masses Á Sherwood Sandstone Á Water-filled silt lagoons

The significance of the excavatability for the successful completion of constructional projects has been recognized in recent years, but little attention has been paid specifically to rotary pile boring. Given the quantity of geological parameters alone which need to be taken into account, it is apparent that the estimation of the drilling rate is difficult. Based on a case study in extremely abrasive tertiary silcretes (quartzite), the engineering geological influences on the drillability are examined. A minutely detailed documentation of the drilling process was produced, and laboratory testing was conducted to gain a better understanding of the correlation between significant rock properties and wear on drilling tools. The examined silcretes (quartzite) show CERCHAR abrasivity indices (CAI) up to a value of more than 6. It comes as no surprise that this highly abrasive rock causes extensive wear on piling equipment and an extremely high consumption of wear parts. In combination with the drilling velocity of both the drill tools and the casing shoe remaining well below 10 cm/min, it is obvious that the drilling performance is significantly impacted in more than one way. A correlation between the lifespan of the wear parts and the net drilling velocity is developed, allowing for a more reliable performance prediction for bored piles.