龙滩重力坝三维仿真与劈头裂缝问题研究

3-D simulation and research on vertical crack on the upstream surface of Longtan RCC dam

龙滩重力坝通航坝段坝轴向长度达88m,下部设2条横缝,无纵缝,不进行接缝灌浆前的二期冷却,坝内温度下降极慢,因此上游面坝轴向应力很大,极易产生劈头裂缝。作者对该坝段施工过程进行了多种工况的温度场与应力场的三维仿真计算。计算结果表明,即使采取了一系列综合温控措施,无保温时,在年变化气温影响下,冬季仍会在上游表面引起2 0～2 2MPa的坝轴向拉应力,寒潮引起的拉应力在3 0MPa以上,二者叠加,可达5 0MPa以上,足以引起表面裂缝,蓄水后会扩展为较深的劈头裂缝。仿真结果表明,用4～5cm厚的苯板贴在上游表面,可将上游表面的拉应力控制在1 6MPa以内,有效地防止表面裂缝的产生,并因此而避免劈头裂缝的产生。

The navigation monolith of Longtan RCC dam is 88 m long along the dam axis. In this monolith, 2 transverse joints were set up in the lower part with no longitudinal joint . The secondstage cooling for joint grouting was not required. The temperature would drop extremely slowly inside the dam body and the axial stress on upstreamsurface would be very high, so that the vertical cracks on upstream surface could hardly be avoided. The authors conducfed a 3-D simulation of the 3D temperature field and stress field under several loadcases for this monolith during the construction process. The calculation results showed that, even if a series of comprehensive temperature control measures are adopted without any insulation on the upstream surface, 20～22MPa tensile stress in damaxial direction on the upstreamsurface will occur in winter under the effect of yearly change of air temperature. 30MPa or higher stress may be caused by cold wave. The total stress would be 50 MPa or higher, which is high enough to produce exterior cracks. Deep vertical cracks on the upstream surface can be induced after reservoir impounding. The results also showed that the tensile stress on upstream surface can be reduced to less than 16MPa by sticking a layer of 4～5cm thick polystyrene plate on the surface, which can effectively avoid the exterior cracks as well as deep vertical crack on the upstream surface.