ABSTRACT
Chalk is known to have a potential risk for natural cavities (solution features) and documenting the location and nature of these geohazards is important to infrastructure projects. North Chilterns Area, one of the five projects within the HS2 Main Works Civils Contract, C23 includes cuttings, embankments and viaducts which will be designed and constructed in the formation of Chalk. The risk of presence of dissolution features in this area is high, either as infilled features near formation level in cuttings and embankments or void or infilled features, being present immediately below the toe of foundation piles, along their shafts, or below shallow footings. This paper discusses the risk from dissolution features for selected high-speed railway assets and presents the approach to investigate their presence based on various ground investigation methods, which were employed on the project. These include LiDAR surveys, surface geophysics (electromagnetic, electrical resistivity, microgravity surveys), intrusive ground investigation (boreholes, CPT probing), use of borehole cameras and downhole surveys. The limitations and advantages of these methods are discussed, highlighting the importance of the combined interpretation of ground investigation data to design appropriate mitigation works.
