Coquitlam大坝抗震能力提高设计(英文)

Seismic upgrade of Coquitlam Dam

Coquitlam 大坝建于 1913 年,坝高 30 m,为吹填土石坝。大坝位于加拿大 BC 省高地震危险带。风险人口数以万计。根据现行标准,大坝的抗震能力不符合要求,坝体冲填土和某些部位地基土松散,容易液化。在中度至重度的地震情况下,大坝将会遭受严重的损坏,并有可能溃决。提高大坝的抗震能力很有必要。选择最高设计地震为里氏7.5 级地震,地震地面水平峰值加速度 0.66g。在设计中,还需要对以下一些提高抗震能力的设计方案进行评估,包括结构修复、大坝重建、限制水库运行及退役。在综合考虑技术、社会、环境和经济因素的基础上,选择了兴建一座新的下游堤坝以提高其抗震能力,减少 Coquitlam 大坝的地震风险。新建坝包括一座土质心墙堆石堤坝和一个位于左坝肩的混凝土过渡带。新建堤坝大部分是建在具有承载力的淤泥土上,而混凝土过渡带则完全建在基岩上。由于现场和施工条件的限制,座落在现有大坝下游坝壳部分的新建堤坝上游坡的下部一小部分为沿原河道的液化砂砾石冲积层。先进的地震稳定性和变形分析结果表明,由于有足够的超高、厚厚的反滤体以及过渡带,大坝所产生的变形是可以接受的。为了控制基础渗流和出逸坡降,设计采用了塑性混凝土防渗墙、帷幕灌浆以及在下游增设一套减压井相结合的方案。为了监测新建坝的性态,在施工期和运行期的仪器监测设计中采用了基于破坏模式的方法。主要介绍了 Coquitlam新建堤坝的设计,包括大坝安全监测系统的设计。

The Coquitlam Dam, constructed in 1913, is a 30 m high hydraulic fill embankment dam. The dam is situated in a region of high seismic hazard in British Columbia, Canada. The population at risk is in the tens of thousands. The dam does not meet the present day seismic safety standards. The hydraulic fills in the dam and some foundation soils are loose and susceptible to liquefaction. Under a moderate to severe earthquake, the dam would suffer severe damage with a possibility of dam breach. Seismic upgrade to the dam is required. The maximum design earthquake is a M7.5 event with a peak ground horizontal acceleration of 0.66g. A range of seismic upgrade options was evaluated, ranging from structural remediation, rebuilding of the dam, restricting reservoir operation to decommissioning. On the basis of technical, social, environmental and economic considerations, constructing a new downstream embankment dam was selected as the seismic upgrade option to reduce the seismic risk of the Coquitam dam. The new dam consists of an earth core rockfill embankment and a concrete transition at the left abutment. The new embankment is mostly founded on competent silt while the concrete transition is entirely founded on bedrock. Due to site and constructability constraints, a small portion of the upstream slope of the new dam sitting on part of the downstream shell of the existing dam is underlain by liquefiable sand and gravel alluvium along the original river channel. Advanced seismic stability and deformation analyses demonstrate that the resulting deformations of the dam are acceptable due to large freeboard and thick filter and transition zones. To control foundation seepage and exit gradient, a plastic concrete cut-off wall, a grout curtain, and a set of downstream pressure relief wells are incorporated in the design. To monitor the behaviour and performance of the new dam, a failure mode based approach has been taken in the instrumentation design for both construction and long term monitoring. This paper describes the design of the new Coquitlam Dam, including the design of the instrumentation for dam safety monitoring.