Design of Concrete

Design of Concrete-Faced Rockfill Dams

As a result of experiences with the earlier concrete- faced rockfill dams, a number of changes in design treatment and construction practice have evolved in recent years:(1)Compacted rockfill , rolled in thin layers, has practically superseded dumped-rock placed in high lifts. It is now almost universally used in the main rockfill sections of modern dams.(2) The upstream dry rubble masonry or placed-rock zone is no longer used. (3) cutoff walls deeply entrenched into the rock have largely been superseded by anchored footwalls which support and seal the periphery of the facing and serve as a grout cap for curtain grouting.(4) The present trend is toward the elimination of deformable joint fillers in vertical joints of the facing and very limited use of horizontal joints.Some or all of these design and construction modernizations have utilized in the two dams selected as examples in the following brief discussions.

1.Cethana Dam

It is 110m high, completed in 1971. The upstream slopes are 1.3H to 1.0V. The main rockfill was sound quartzite. The rock was placed in layers 0.9m thick and rolled with 4 passes of a 10-ton vibratory roller. Immediately preceding and during compaction all rockfill was sprayed with water, the volume applied being not less than 15 percent of the rockfill volume. This procedure produced a relative density of the rockfill close 100 percent. Within the downstream one-third of the section, lifts 1.35m thick were used and the gradation limits for the rockfill were wider than for the main rockfill. A zone about 3.0m wide in the upstream part of the main fill was composed of specially selected rock and compacted in 0.45m lifts.To ensure good compaction of the fill immediately beneath the facing, the upstream face of the rockfill was initially given 4 passes of the roller without vibration, and the slope was trimmed to remove high spots. It was the given 4 passes at half vibration and low areas were filled. To avoid displacement by roller vibration, traffic , and rain , a bitumen emulsion treatment was applied. The final compaction was attained by 8 passes of the roller with full vibration.The final compaction was attained by 8 passes of the roller with full vibration.

The concrete facing was slip formed in panels 12.2 m wide with horizontal contraction joint except near the periphery where intermediate vertical joints , terminating in horizontal contraction joints, were introduced to control cracking of the slab in zones where horizontal tensile strains were expected. These horizontal joints contained wood filler strips, but no filler of any kind was used in the vertical joints. The conctrete facing was ta pered according to the formula “t=0.3+0.002h ” where “t=” Thickness and “h=”hydraulic head, in meters. The plinth or footwall at the lower periphery of the facing was not entrenched but cast on the rock surface after removal of weathered and open jointed rock. The plinth was dowelled to the foundation to withstand the consolidation grouting pressures.

Instrumentation installed at Cethana provided comprehensive data on the structure during construction, first filling of the reservoir, and for a short period of operation. A few of the findings are cited for comparison with performance data

on dumped rockfill dams.

During construction, settlement was approximately proportional to height of rockfill when rock was placed continuously. Creep settlement continued with no increase in fill loading. A high rate of settlement continued for up to 2 months after the top 12m of rockfill was placed and after the reservoir was filled.The vertical and horizontal deflection of t he crest during a period of about 11 months following the commencement of filling the reservoir were : maximum vertical = 69 mm, horizontal downstream maximum = 41 mm, horixontal transverse =18mm toward center from left and 8mm toward center from right. The deflection of the membrane was essentially normal to the face and was a maximum of about 13mm at about the lower 0.4 point of the slope.The maximum perimetric joint opening was about 11.5mm.After filling the reservoir the strains in the facing were compressive, the maximum being 207×10-6 in the slope direction and 290×10-6 in the transverse direction.The leakage past the dam at full reservoir was 0.035m3/s.

2.New Exchequer Dam

It is 149.5m high, completed in 1966. The dam is unique in that it incorporates the old 94.55m high concrete gravity arch dam in the upstream heel as a retaining wall for the rockfill of the new dam, and as the lower part of the upstream impervious membrane on the face of the new dam.

The slopes of the dam, both upstream and downstream, are 1.4H to 1.0V.The rockfill was placed in 4 zones, as follows: the zone immediately under the concrete facing consists of 38.1 cm maximum size rock compacted in 0.61m lifts by a 10-ton vibratory rollers. An upstream zone adjacent to the old dam and extending to the top of the new dam, varying in width from about 61 m at the bottom to about 12.2m at the top, was constructed of 1.22m maximum size rock placed in 1.22m lifts and compacted by 10-ton rollers.The main body of the dam consists of 1.22m maximum size rock placed in 3.1m lifts and compacted by hauling and grading equipment.The downstream slope section of the dam consists of largest rock which could be placed with a minimum of 50 percent larger than 30.48m.

The fill material was dumped in lifts up to 18.3m high but no compaction was specifiedAll the fill except the zone immediately under facing was sluiced ()with high pressure jets. The New Exchequer Dam rockfill represents a compromise or transition between the traditional practice of dumping rock in high lifts without compaction and the more recent trend toward heavy mechanical compaction of the fill in relatively thin lifts.

Measurements made during construction and during the first filling of the reservoir showed normal movements of the facing slabs, with the vertical joints near the center tending to close and those near the abutments tending to open.

After the reservoir was filled the maximum crest settlement was 0.46m or about 0.3 percent of the height.

The maximum horizontal downstream movement of the crest w％as 12.2cm

or about 30 percent of the associated vertical movement.

During the first two fillings of the reservoir the leakage through the dam increased form 0.35m3/sec to a maximum of 13.72 m 3/sec.

This was caused by the spalling and cracking of the face slabs at and near the junction of the new facing with the old dam.

A supplementary zone composed of sand, gravel, clay, and bentonite was placed underwater in the “V” notch formed at the contact of the new facing with the downstream facing of the old dam.

This material was placed to a depth of 6.1m to 7.6m using a specially designed skip.

The sealing blanket reduced the leakage to about 0.224m3/sec.

要求：翻译成中文。

面板堆石坝的设计

根据早期面板堆石坝的经验结果，近年来在设计方面的处理和施工实践发生了一系列的改变。这些改变包括：（1）对薄层进行碾压的压缩式填石在实际应用中已经取代了铲运机的抛石填充。现在这种施工方法几乎作为现代大坝的主要石头填充方法。（2）上游干砌石或放置岩带已经不再使用。（3）深入岩基的防渗墙大部分被底板锚固所取代，而底板锚固是支撑和密封边缘面并用帷幕灌浆作为一种灌浆覆盖。（4）当前的趋势是根除在垂直节理面的可变形填充点以及对水平点的使用限制。一些或所有的那些设计及施工现代化已经在两座大坝中使用，举以下实例来做详细讨论。

1、塞沙那坝

塞沙那坝坝高110米，在1971年竣工。上游坡度为1.3:1.0。主要的填充石料为完好的石英岩。填充石放成0.9米厚的石层，并用4辆10吨重的振动碾压机对石层进行碾压。在碾压之前和压实过程中，所有的填石要喷洒不少于填石体积15%的水。在这个施工中接近100%的填石相关密实度。在下游三分之一的区域里，填石厚度升为1.35米并且对填石的等级也要比主要填石的要求更宽。在上游主要填充部分中有三米宽的区域应特别选择组成岩石，并且升高0.45米来压实。为了确保填充表面以下压实质量，上游的填石表面将会用4台无振动的碾压机，还要求坡度修改其高点。用给的四辆半振动的碾压机来填充低的地区。为了避免振动碾压机、机械以及雨水带来的位移，这里采用乳化沥青处理来解决这一问题。最后的压实需要八台全振动碾压机来工作实现。

混凝土面引进控制除了横向拉伸应变的区域裂缝板，而此混凝土面是在除了有中间垂直节理和处理横向缩缝的边坡的12.2米的带有横向缩缝的控制板的滑移形式。那些横向缝包含木

嵌条，但是在垂直缝中不是所有的填充类型可以用。混凝土面是根据公式

减缩的，公式中的t表示厚度，h表示水头，单位为米。在低面边坡的基座或底板不能挖掘，但是可以在移除风化和开裂的岩石后的岩石表面。底座与基础用锚杆连接用以抵抗固结灌浆压力。

在塞沙那坝设置的仪器为在施工、首次蓄水以及短时间内操作期间的结构提供广泛的数据。一些发现被引用来做抛石坝的性能数据比较。

在施工过程中，当岩石连续放置沉降是与填石高度大约成一定比例。缓慢沉降是在无增长的填土荷载下持续进行的。在填石达到12米高和水库蓄水后，高的沉降率会持续两个月。在从开始水库蓄水到十一个月这一段时期，大坝的横向及垂直偏移达到顶点：最大垂直偏移为69毫米；下游的最大横向偏移为41毫米；横向水平从左向中心为18毫米，从右向中心为8毫米。膜偏移相对于面是很正常的，并且在边坡以下0.4点膜偏移最大值为13毫米。最大的周边开裂为11.5毫米。在蓄水以后，表面拉应力是很复杂的，在坡度方向最大为

，在横向方向为。在水库各处的渗流速为。

2、新埃克斯切凯尔坝

新埃克斯切凯尔坝坝高149.5米，竣工于1966年。该大坝非常独特，它是在一座94.55米高的混凝土重力坝的旧坝上建的新坝，上游坡脚依靠在旧坝下游面上，把旧坝作为新坝上游挡土墙，并采用混凝土面板作为防渗结构，形成一个连续的上游不透水层。

大坝的上游和下游的坡度都是1.4:1.0。填石放置分为四个区域，分别是混凝土面以下区域是由最大粒径为38.1厘米的岩石填充，并由十吨重的振动碾压机每0.61米为一层进行压实；上游区域邻近旧坝，并将其延伸至新坝的最高点，从坝底的61米到坝顶的12.2米宽度不等，填充粒径不大于1.22米的岩石，每1.22米用十吨的碾压机将其压实；大坝主体是由不大于1.22米的岩石填充而成，每3.1米用牵引和分级设备将其压实；大坝的下游坝坡区域的填充石的粒径最大的至少有50%是大于30.48米的。

填充材料倾倒升高到18.3米高，无压实是非常特殊的，除了表面区域其它所有区域被高压喷射冲实。新埃克斯切凯尔坝填石代表一个折中方案或者过渡，即在高升降无压实反倾岩的传统实践与近来更多趋向重机械压实相对较薄的填充方法。

在施工和首次蓄水期间采用的措施会显现在面板的正常移动上，即中心附近的垂直裂缝趋向闭合而对接附近的缝则会张开。

在库水蓄满后，最大的坝顶沉降为0.46米或者大约为坝高的0.3% 。

最大的下游顶部水平移动为12.2厘米或者大约为相关垂直移动的30% 。

在前两次水库蓄水过程中，通过大坝的下泄流量从增加到。

这是由面板的剥落与开裂和旧坝与新坝面的结合点附近引起的。

由沙、砾石、黏土、膨土岩组成的补充物以V形槽放在水下，用来联系新坝面与下游旧坝面。

这种材料放在6.1米到7.6米深处用专业地设计跳过。

密封的覆盖层减少渗漏约。