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1、8 RCC as a New Construction Method（ RCC 作为一种新的施工方法）8.1 General Construction Considerations 一（ 般情况下施工过程需考虑的因素 ）There are con siderable differe nces betwee n vertical, block-by-block con structio n （垂直 块 状 浇 筑 ） of dams with conventional mass concrete and horizontal, lift-by-lift construction （水平通仓浇筑）
2、of dams with RCC. The construction plant for RCC is usually, less costly, and utilized at a higher capacity factor （利用率） than that required for conventional concrete gravity dams. But the fast pace of placement required to achieve the economies possible with RCC imposes a greater discipli ne 要求）on t
3、he pla nning, scheduli ng进度）,and coord in ati on（协 调）in the field betwee n desig ner设计）and con tractor承 包商）. The RCC design approaches described in Chaps. 4, 5, and 6 diverg不同点在于 .） in some construction procedures. In all cases, however, the mixing（拌合）,transporting（运输）,spreading摊铺）,and compacting （碾
4、压）of relatively large volumes of material are concentrated into a short time interval. In the United States, the time limit from mixing plant to final compaction is about 45 min. It is about twice that in Japan. In addition, the JapaneseRCD method requires that lifts be cured （养护）for as long as 36 h
5、 before placeme nt （浇筑）of the n ext layer of RCC. In the United states and elsewhere, the goal has nearly always been to come as close as possible to continuous placement of RCC.Construction scheduling for RCC is less forgiving than for mass concrete大体积混凝土 ）. Although some mix designs can have great
6、er tolerances than conventional concrete, RCC is still a sensitive concrete and the critical path （关键路线 ）for placing RCC is focused on complet ing one lift at a time. There are no alternate mono lithic 整块的、独块的）blocks to form or place while problems are being analyzed.To avoid costly delays over disp
7、utes on specification规范）complianee （执行）,the authority to resolve engineering problems must be vested in a well trained field orga ni zati on. Lines of com muni cati on betwee n the project engin eer （项目工程师） and con tractor must be clearly established and used freque ntly. Clarit廉洁）,can dor （坦诚）， and
8、 cooperation are very important in achieving the speed of placement possible with RCC.Thorough field and classroom training of construction crew（s 施工队伍） and inspectors （检查员） in the handling and placement of RCC is essential. Lean, dry RCC mixes resemble damp （潮湿的） gravel （砂砾石）and are often placed by
9、 road-building or earth-dam crews using earthmoving equipment. However, all the desired characteristics of the product are those of concrete. Meeting the specifications requires educating workers to the specific requirements of RCC as a new construction material requiring specific construction metho
10、ds.Because so much depends on fast, efficient placement of the RCC, all related activities such as foundation cleanup, access, assembly of embedded components预埋件）,and stockpiling （贮存、堆存） of materials must be meticulously planned and scheduled well before construction starts. Construction of forms an
11、d assembly of embedded items should be planned and scheduled so that as much of the work as possible is done off the dam, or if necessary, from the top of a lift （升程）during shift （工作班）changes.Lift scheduling is often complicated by concerns over heat buildup. Because the production rate of RCC can b
12、e very high, controls to limit thermal cracking （温度裂缝） may restrict the seasonor time of day that placement is allowed as well as the rate of placement.At Upper Stillwater Dam, all of the RCC was placed during a five-month weather window each year from May to October and only during two 8-h shifts s
13、tarting at 8 p.m. This was necessary in order to keep placement temperatures below the 50oF （10oC） specification limit. At Willow Creek and Galesville dams, placement was limited to no more than three and four lifts, respectively, each 24 h.Conversely, at Elk Creek and Stagcoach dams, the contractor
14、 was encouraged to place RCC as fast as possible. At peak placement, six 1-ft (0.3-m) lifts were placed in a day at Stagecoach. The 150-ft-high (46-m) dam required 44,500 y3d(34,000 m3) of RCC which was placed during 37 days in the summer of 1988. To keep placement temperatures low at Elk Creek, the
15、 specifications required that the most massive sections be constructed during the late winter and early spring.8.2 Aggregate Production and Plant Layout 砂( 石料生产和混凝土工厂布置 )Maintaining adequatesupplies of acceptable aggregateis particularly important to RCC scheduling. More than half of the aggregate r
16、equired for an entire construction season may need to be stockpiled well ahead of the start of construction in order to keep up with extraordinarily high demand during the placement season.This can also provide some easing緩解)of cash flow (现金流)and scheduling requirements during the placement season. Large stockpiles also allow for more economical sizing of production facilities and for blending of material that may be out of specification. If precooling of
