Abstract:
This paper presents the design, construction, instrumentation, and long-term performance of a permanent soil-nailed retaining wall constructed in highly fractured karstic limestone. The works were delivered as part of a major residential development in south-eastern Turkey, a large housing scheme comprising approximately 3,500 dwellings arranged around extensive artificial lakes and landscaped areas. The site topography and adjacent roadway constraints required near-vertical retaining sections reaching up to 15 m in height. The adopted solution comprised encapsulated permanent soil nails installed in predrilled and post-grouted boreholes, supported by a temporary shotcrete and welded-wire mesh facing between nail head plates, and completed with a permanent cast-in-situ reinforced concrete facing incorporating architectural features.
More than 1,800 permanent nails were installed along a 560 m alignment. Nail lengths ranged from 6 m to 14 m, and mechanical couplers were used where required and verified through testing. Ground conditions behind the wall comprise very weak, highly fractured limestone with micro-karstic cavities, resulting in spatial variability in drilling response, grout take, and local bond conditions. The ground investigation programme for the first phase included 69 boreholes to depths of up to 60 m, supported by extensive in situ and laboratory testing. Nail pull-out resistance was initially estimated using results from 265 high-capacity Menard pressuremeter tests and 364 unconfined compressive strength tests, and subsequently verified through full-scale verification and proof load tests. Wall performance was monitored using eight deep inclinometers distributed along the wall alignment to capture deformation trends during excavation, facing construction, and service conditions.
A key aspect of this study is the observed performance of the wall during strong earthquake shaking associated with the 2023 Kahramanmaras earthquake sequence. Despite experiencing significant regional ground motions, the retaining system did not exhibit observable damage, distress to the facing, or serviceability issues. The paper reviews the likely impact of the earthquake loading on wall stability and deformation demand, drawing on the project’s instrumentation records, post-earthquake inspections, and the original design assumptions. Observed wall deformations are also evaluated against numerical analyses undertaken during design, and construction challenges associated with drilling and grouting in karstic limestone are discussed. The outcomes provide practical lessons for the design and implementation of permanent soil-nailed walls in highly variable karstic rock, and for demonstrating robust seismic performance through a combination of testing, monitoring, and post-event assessment.