高寒地区低热水泥混凝土拱坝温控防裂方案

Temperature control and crack prevention scheme of low heat cement concrete arch dam in high cold area

高寒地区年平均气温低、昼夜温差大,拱坝易产生温度裂缝,从筑坝材料源头就降低温升,可进一步降低拱坝开裂风险。开展中、低热水泥混凝土拱坝温度场、应力场的对比分析;进行低热水泥混凝土拱坝温控措施优化比选;形成适合高寒地区低热水泥混凝土拱坝的温控防裂方案。结果表明:低热比中热水泥混凝土拱坝最高温度低4.0℃左右,应力最大值低0.7 MPa左右,安全系数从2.48提升到3.65;低热水泥混凝土拱坝可放宽约束区冷却水管间距至1.5 m×1.5 m,强约束区浇筑层厚可从1.5 m放宽至3.0 m,坝体表面流水措施可取消,夏季浇筑温度可放宽至16.0℃,冬季实现常温浇筑;脱离约束区,高温季节5-9月浇筑温度可放宽至18.0℃,层厚对大坝最高温度及应力影响较小,因此可放宽至6.0 m;大坝采用全年永久保温,等效放热系数取β≤3.05 kJ/(m~2·h·℃)。研究结果验证了低热水泥混凝土拱坝抗裂性能的优势,给出高寒地区温控优化措施,实现大坝快速施工,进一步降低了温控和施工成本。

The frigid regions were characterized by low annual average temperatures and significant diurnal temperature variations,which made it prone for dams to develop temperature cracks.The conventional high concrete arch dams at that time utilized a mix of"moderate heat Portland cement with 35%Class I fly ash".Despite achieving the then-current advanced level of temperature control measures,the safety factor for concrete crack resistance remained at approximately 1.8.Consequently,it was imperative to conduct research on temperature control and crack prevention,starting from the very source of the materials.With the concrete double-curvature arch dam of a hydropower station in Xizang as its research backdrop,low-heat cement concrete was chosen as the dambuilding material.By reducing the temperature rise from the source of the material,it aimed to further mitigate the risk of cracking.Drawing upon the theories of unstable temperature and stress field calculations,a comparative analysis of the temperature and stress fields between moderate-heat and low-heat cement concrete arch dams was conducted,highlighting the advantages of using low-heat cement concrete for dam construction.Following this,it optimized and compared various temperature control measures for low-heat cement concrete arch dams,ultimately formulating a tailored temperature control and crack prevention strategy suitable for frigid regions.The results indicated that the maximum temperature of the low-heat cement concrete arch dam was approximately 4.0℃lower than that of the medium-heat cement concrete dam,and the maximum stress was reduced by about 0.7 MPa.Moreover,the safety factor was elevated from 2.48 to 3.65.For low-heat cement concrete arch dams,the spacing of water cooling pipes in the constrained zone could be relaxed to 1.5 m×1.5 m,and the thickness of the pouring layer in the strongly constrained zone could be increased from 1.5 m to 3.0 m.The water flow measures on the dam surface could be eliminated,and the pouring temperature in summer could be relaxed to 16.0℃,allowing for normal temperature pouring in winter.Outside the constrained zone,during the high-temperature season from May to September,the pouring temperature could be appropriately increased to 18.0℃.The thickness of the layer had a minor impact on the maximum temperature and stress of the dam,permitting an extension to 6 m.The dam adopted permanent thermal insulation throughout the year,with a equivalent heat release coefficient ofβ≤3.05 kJ/(m^(2)·h·℃).These research outcomes validated the superiority of low-heat cement concrete arch dams in crack resistance and provided optimized temperature control measures for frigid regions.They facilitated rapid dam construction while further reducing temperature control and construction costs,offering technical guidance for the application of low-heat cement in frigid regions.