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<p>Geothermal fluids can modify the physico-mechanical properties of carbonate rocks on engineering-relevant timescales; however, field-anchored, time-resolved datasets remain limited. We conducted an in situ exposure experiment within an active karst sinkhole in the Kozakli geothermal field (Central Anatolia, Turkiye) to quantify changes in travertine properties over 3–9 months and to propagate the measured changes into scenario-based finite-element analyses using Phase2 (Rocscience Inc.). NX-size cores (nominal diameter 54.7&#xa0;mm) were assigned to four groups: one group was tested in the laboratory as a fresh baseline, and three groups were deployed in the sinkhole and recovered after approximately 3, 6, and 9 months. Field water-quality descriptors (temperature, acidity–alkalinity expressed as pH, and electrical conductivity) were measured during two campaigns to provide hydrochemical context. Physical and mechanical tests (ultrasonic P-wave velocity, uniaxial compressive strength, point-load index, density, porosity-related indices, and slake durability) were performed for the baseline and for each retrieval. Four independent numerical models (baseline, 3, 6, and 9 months) were run under saturated travertine assumptions using period-updated laboratory means. The results indicate (i) elevated electrical conductivity at thermal outlets (up to approximately 7400&#xa0;µS/cm) with near-neutral to mildly acidic pH (6.34–7.67), (ii) a reduction in dry uniaxial compressive strength from 20.90&#xa0;MPa (fresh mean) to 19.11&#xa0;MPa after approximately 9 months and a 9–17% reduction in dry ultrasonic P-wave velocity relative to baseline together with increasing void ratio (2.47–9.96% relative change), and (iii) numerical stability metrics that decrease when the period-updated properties are imposed, with the critical strength reduction factor (SRF; a factor-of-safety proxy) decreasing from 2.88 in the baseline scenario (enlarged domain) to 2.39 in the 9-month scenario. In addition, strength-factor contours at SRF = 1.00 indicate a reduced stability margin concentrated around the cavity roof and shoulders as exposure time increases. These trends are compatible with exposure-related weakening under saturated conditions; however, the hydrochemical dataset is limited to pH, temperature, and electrical conductivity descriptors (no alkalinity, dissolved inorganic carbon, dissolved gases, saturation-index calculations, or reaction-path modeling), and the numerical results are conditional on simplifying assumptions (two-dimensional plane strain, fixed rock-mass descriptors, and no coupled seepage). Future work should implement seasonal major–minor ion and alkalinity/dissolved-inorganic-carbon sampling, compute carbonate saturation indices for calcite and dolomite, and couple seepage with mechanical modeling to relate chemical conditions to time-varying strength, stiffness, and stability metrics.</p>

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Geothermal fluid–rock interaction and its impact on physicomechanical behavior: evidence from in-situ sinkhole exposure experiments

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月12日

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  • Halil Boluk,
  • Mustafa Afsin,
  • Mustafa Murat Kavurmaci,
  • Mutluhan Akn

摘要

Geothermal fluids can modify the physico-mechanical properties of carbonate rocks on engineering-relevant timescales; however, field-anchored, time-resolved datasets remain limited. We conducted an in situ exposure experiment within an active karst sinkhole in the Kozakli geothermal field (Central Anatolia, Turkiye) to quantify changes in travertine properties over 3–9 months and to propagate the measured changes into scenario-based finite-element analyses using Phase2 (Rocscience Inc.). NX-size cores (nominal diameter 54.7 mm) were assigned to four groups: one group was tested in the laboratory as a fresh baseline, and three groups were deployed in the sinkhole and recovered after approximately 3, 6, and 9 months. Field water-quality descriptors (temperature, acidity–alkalinity expressed as pH, and electrical conductivity) were measured during two campaigns to provide hydrochemical context. Physical and mechanical tests (ultrasonic P-wave velocity, uniaxial compressive strength, point-load index, density, porosity-related indices, and slake durability) were performed for the baseline and for each retrieval. Four independent numerical models (baseline, 3, 6, and 9 months) were run under saturated travertine assumptions using period-updated laboratory means. The results indicate (i) elevated electrical conductivity at thermal outlets (up to approximately 7400 µS/cm) with near-neutral to mildly acidic pH (6.34–7.67), (ii) a reduction in dry uniaxial compressive strength from 20.90 MPa (fresh mean) to 19.11 MPa after approximately 9 months and a 9–17% reduction in dry ultrasonic P-wave velocity relative to baseline together with increasing void ratio (2.47–9.96% relative change), and (iii) numerical stability metrics that decrease when the period-updated properties are imposed, with the critical strength reduction factor (SRF; a factor-of-safety proxy) decreasing from 2.88 in the baseline scenario (enlarged domain) to 2.39 in the 9-month scenario. In addition, strength-factor contours at SRF = 1.00 indicate a reduced stability margin concentrated around the cavity roof and shoulders as exposure time increases. These trends are compatible with exposure-related weakening under saturated conditions; however, the hydrochemical dataset is limited to pH, temperature, and electrical conductivity descriptors (no alkalinity, dissolved inorganic carbon, dissolved gases, saturation-index calculations, or reaction-path modeling), and the numerical results are conditional on simplifying assumptions (two-dimensional plane strain, fixed rock-mass descriptors, and no coupled seepage). Future work should implement seasonal major–minor ion and alkalinity/dissolved-inorganic-carbon sampling, compute carbonate saturation indices for calcite and dolomite, and couple seepage with mechanical modeling to relate chemical conditions to time-varying strength, stiffness, and stability metrics.