三峡工程一期纵向碾压混凝土围堰施工工艺

Constriction techniques of the longitudinal RCC cofferdam in the first phrase of the Three Gorges Project

三峡一期工程纵向碾压混凝土围堰混凝土工程量１５９．２万ｍ３，其中碾压混凝土占８１．８％。围堰堰坝段和下纵段为永久建筑物，上纵段为临时建筑物。围堰混凝土采用自卸汽车运输，上纵段和下纵段汽车直接入仓浇筑，堰坝段汽车运输转料，罗泰克胎带机入仓浇筑。碾压混凝土采用间歇上升施工，每一个浇筑升程（１．８～２．４）ｍ，一般间歇５ｄ左右浇筑下一个升程。为保证升程之间的层面结合，砂浆必须具有一定的流动性，坍落度（６～８）ｃｍ，并要求随铺随卸料，为确保浇筑层间的层面结合，混凝土中掺高效缓凝剂ＪＧ４，并严格控制层面暴露时间，冬季小于（６～８）ｈ，其它季节白天小于４ｈ，夜间小于６ｈ。施工中一层碾压混凝土（３０ｃｍ）分二次铺料，即先铺下半层（１５～２０）ｃｍ，再铺上半层，可较有效地解决骨料的分离问题，有利于保证层面和混凝土施工质量。

The concrete volume of the longitudinal roller compacted concrete cofferdam in the first phrase of ThreeGorges Project is 1. 592 million m3, among which the roller compacted concrete accounte for 81. 8%. The dambody section and the lower longitudinal section of the cofferdam are permanent structures but the upper longitudinal section is temporary structures. The concrete for cofferdam is transported by dump truck. In the lower and upper longitudinal sections, the dump truck can directly pour the concrete in the placement. The concrete pouring inthe dam section is made by belt conveyor. The construction of roller compacted concrete is made by the intermittentconstruction method. Every placing lift is 1. 8-2. 4 m and the interval period is about 5 days. In order to guaranteethe combnation between the lift layer surface, the mortar should have certain flowability and its slump of 6-8 cmand should be required to place as it is discharged. In order to ensure the interlayer combination between the pouring layers, the high effective retarding agent of JG4 is mixed in the concrete and the layer exposure time is seriouslycontrolled, which is less than and/or equal to 6-8 hours in winter, and 4 hours in daytime and 6 hours at night inother seasons. in the construction, one layer concrete (30 cm) should be placed in twice, that is, lower half-layer(15-20 cm) should be placed firstly and then the upper half-layer is done. This could effectively solve the detachment between the aggregates, which would be favorable to guarantee the quality of the layyer surface and the concrete construction.