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