https://indico.cern.ch/event/1607311/contributions/6772233/attachments/3164312/5623166/The_ET_Baseline_Detector_Layout.pdf

The investment for Einstein Telescope (ET) construction will be dominated by the cost of underground civil infrastructure. The corresponding costing will be based on engineering studies carried out by specialized com- panies employed by the teams preparing possible ET sites (referred to as “Local Teams” in the following). In 2024 a preliminary detector layout for both the Triangle and the 2L geometry was generated by the Engineer- ing Department (ED) of the ET Organisation (ETO), based upon an update of the ET optical layout by the Instrument Science Board (ISB) of the ET scientific Collaboration (ETC). Such preliminary detector layouts are indicated as “2024 reference” throughout this document. Early feedback based on engineering expertise associated with the work at the Local Teams indicated that the design philosophy of the 2024 reference layout would lead to substantially higher cost for the civil infrastructure than expected in the conceptual ET plan submitted as part of the ESFRI proposal in 2020. Upon request of the ET Coordinators, ETO agreed to set up a task force, coordinated by the ETO Technical Coordinator reporting to the ETO Directors. The task force sourced personnel and support from the ET Collaboration (ETC), ETO, the civil engineering specialists of the local teams and from CERN, as well as from external projects or institutions as needed