CAJG 2018: TOPIC 3 Engineering geological assessment using geochemical, mineralogical, and petrographic analysis along the Riyadh Metro Line 3 (Saudi Arabia) Manuel Cueto 1 & Carlos López-Fernández 2 & Luis Pando 2 & Daniel Arias 2 Received: 6 July 2019 /Accepted: 7 January 2020 # Saudi Society for Geosciences 2020 Abstract Geological constraints are one of the main causes of delays and excessive costs during engineering projects, especially in underground and foundation works within challenging geotechnical conditions like Riyadh’ s subsoil. Bad ground behavior is usually connected to its chemical and mineralogical composition. Integrated geological testing, which combined geochemical (462 X-ray fluorescence and Leco), mineralogical (406 X-ray diffraction), and petrographic (11 polarizing microscope) analysis, was carried out prior to construction to preliminarily assess soil and rock behavior. This investigation protocol seeks to shed light on the geological composition, geotechnical features, and finally potential impacts on the construction along Line 3 of the Riyadh Metro Project, the largest metro project ever built from scratch. The quantity of geological tests done was almost certainly higher than ever before in the engineering field due to the project’ s importance and the potential subsurface geotechnical problems. The preliminary judgments made with initial geological tests were further confirmed with more than 1300 geotechnical tests. This paper shows the results of each individual geological method and how the multi-technique geological testing resulted in an effective preliminary characterization of the ground, enabling us to anticipate geotechnical impacts. However, the ground behavior cannot be fully addressed with geological analysis and thus confirmatory geotechnical tests must always be carried out when designing infrastructure construction projects. Keywords Engineering geology . Geochemistry . Mineralogy . Petrography . Riyadh Metro . Saudi Arabia Introduction Geological constraints are one of the main causes of construc- tion delays and excessive costs in large infrastructure projects. These constraints increase schedule and construction over- heads and are mainly reported in literature with regard to un- derground (Ioannou 1988; Zarei et al. 2012) and foundation works (Sabtan 2005; Abdeltawab 2013; Yassin et al. 2014). For example, according to Gattinoni et al. (2012), the occur- rence of an unforeseen geological event can produce a 30% increase in time and costs of the whole tunnel project. Similarly, more than 60 countries are suffering from expansive soil damage to foundation structures which cost billions of dollars worldwide (Aqeel 2016; Puppala and Pedarla 2017). Over the years, countless projects around the world have faced severe challenges due to insufficient or inappropriate geological assessment and investigation. Extra costs arising from a lack of site investigation planning and interpretation tend to account for around half of the total additional costs (Tyrrell et al. 1983). Any attempt to reduce costs with a limited site investigation may result in consequential additional ex- penditure if unexpected and unfavorable ground conditions are later encountered during construction (Bell 2004). A ques- tion which often arises when planning a geotechnical survey protocol is how many samples should be taken and which kinds of tests should be performed to ensure a proper subsoil characterization. According to González de Vallejo and Ferrer (2011), approximately 15–25% of any total project design cost This paper was selected from the 1st Conference of the Arabian Journal of Geosciences (CAJG), Tunisia 2018 Responsible Editor: Amjad Kallel * Manuel Cueto mcueto@idom.com 1 IDOM Consulting, Engineering and Architecture, Avda. Monasterio de El Escorial 4, 28049 Madrid, Spain 2 Department of Geology, University of Oviedo, Jesús Arias de Velasco s/n, 33005 Oviedo, Spain Arabian Journal of Geosciences (2020) 13:99 https://doi.org/10.1007/s12517-020-5091-8