Our rail specialists performed site investigations to characterise, interpret and advise on karstic conditions and associated ground risk along a 13.8 km section of the Albhochfläche (Swabian Alp Plateau), part of Deutsche Bahn’s Wendlingen to Ulm high-speed railway.
Challenge
The region is characterised by unpredictable ground conditions that are potentially unsafe, including voids, that created challenges for the design and construction of the high-speed rail link.
Solution
A dedicated multidisciplinary team ensured the efficient delivery of a range of site characterisation, testing and monitoring services to guide foundation design and construction over a 6-year period. Data were used to inform foundation design of all critical structures and to establish the requirements for karst rehabilitation, with Fugro also providing earthwork quality control.
Methodology
Approach
Drawing on our global experience in karstic ground conditions, our specialists devised a phased methodology based on geophysical site-screening to minimise intrusive testing. Combined seismic and microgravity surveys provided continuous subsurface imaging along the route to identify low-density features that required boreholes for further geotechnical investigation.
This targeted approach reduced programme time, cost and risk, as it avoided the need to drill every 2 m to investigate ground risk; a large drilling programme would also have been complicated by the nearby BAB A8 motorway.
Modelling
Our specialists created a robust ground model that fully characterised the karst and then advised on effective solutions for stabilising the earthworks and foundations. We provided cut-and-fill calculations, quality control, advice on earthwork compaction, foundation design, and soil engineering that all conformed to Deutsche Bahn’s required technical standards.
Time-savings
To stagger the foundation work effectively, we provided calculations and data to demonstrate the stability and conformance of the proposed remediation design to rail and ground engineering standards. Our onsite laboratory swiftly assessed the quality and compaction properties of soil excavated from the karstic areas, and advised on the mix design, including binder treatment, to improve the soil for reuse.
We also provided:
- Geological mapping via core-and-hammer boring and trial pitting;
- Cone penetration testing (CPT) and dynamic probing;
- Dam, embankment, and environmental monitoring;
- Geotechnical and earthwork guidance for construction of the tunnel boring machine (TBM) used for the starting ramp to the Aichelberg tunnel, located within the Albaufstieg (Swabian Alp Ascent).
All data and information were managed and visualised using our in-house database Software GeODin®, enabling stakeholders to easily access georeferenced results.
Innovation highlight
Designed with a deformation tolerance of just a few millimetres, the high-speed line required a full and reliable characterisation of the karstic conditions. To maximise ground clarity, we used innovative geophysical techniques before and after the geotechnical testing. First, a hybrid seismic investigation coupled with microgravity was performed to provide high-resolution imaging along the track to target and therefore minimise drilling. Seismic cross-hole tomography was then paired with the borehole test results to help verify and enhance the geotechnical data. This established the presence of any voids and the surrounding ground strength with high accuracy to increase confidence in ground characterisation at the bridge and underpass locations.
Impact
Through constant communication and a highly flexible approach, we provided high quality geological insight and earthwork quality assurance to meet the ground engineering schedule of the client and their subcontractors.
Our multidisciplinary support reduced the number of interfaces and administrative burden of using several contractors. We coordinated project data and tasks for maximum efficiency, reducing duplication and margin of error whilst fast-tracking deliverables to the client.
This comprehensive approach to ground-risk mapping and karst remediation supported the design of a safe high-speed track conforming to Deutsche Bahn’s specifications, which contributed to reliable track performance and accurate journey times for the benefit of both the train operator and their passengers.