风英文翻译分析和总结.docx

英文翻译综述The absence of catastrophic consequences resulting from crack formation can be explained by the compara- tively shallow depth of crack development and the effective performance of the drainage, which is a mandatory structural element for the dam and subsurface contour.Fulfillment of the above-cited standard requirements results in the fact that the compressive strength of the concrete is not fully developed (usually by 10- 15%), As a result, the volume of a gravity dam, as a rule, signifi- cantly exceeds the volume of a buttress dam, in which the properties of the material are more fully utilized. As a result of this, the gravity dam is frequently not considered, although it always attracts attention due to the sim-plicityof its design, which makes it possible to employ the most inexpensive means of placing concrete; to its size, which is smaller than other types of dams; to the dependence onthe quality of the foundation; and to the possibility of obtaining a compact grouping of basic structures within the hydraulic facility. These advantages offered by gravity dams compel us to search for new means of improving their design in order to reduce their cost.As one approach, we can propose the following:1. Select the shape of the dam from the compressive strength of the concrete in the zone of its downstream face, the strength of the foundation beneath its base, and the ability of the dam as a whole, and of its individual parts, to resist plane shear and overturning;2. Assuming the formation and exposure of cracks, do not restrict the magnitude of the tensile stresses in the upstream face, including the contact zone;3. In order to exclude the counter pressure exerted by water in the cracks and to realize structural mea- sures: a) Install an anti-seepage curtain on the upstream face and develop a drainage system directly behind it, assuming that the basic purpose of the curtain is to minimize the seepage into the drainage system; and, b) carry the grout curtain upstream and construct a reliable union between it and the dam.The effect of the conditions required for the state of the pressure (upstream) face and the level of stresses in the gravity darn mass (with observance of standard requirements concerning the shear strength with a basic loading combination) is illustrated graphically inTable 1 and in Fig. 1. A comparison of dam shapes is made with tan0= 0.75 and C = 25 tons/m2. The volumes represented by the shapes are given including coupling between the dam and curtain.A less massive gravity dam was designed in accordance with these principles for the conditions prevailing at theKurpsai hydraulic facility (1973) by the All- Union Lenin Order S. Ya. Zhuk Scientific-Research Institute for Design and Exploration. As we pass over the problem of groupings which should be closely linked with the structural and technological characteristics of the dam, we can only provide a description of the designs that guarantee reliable service of a dam where cracks are permissible in the upstream face and along the contact with the foundation, and the results of computations and experimental investigations.A dam (Fig. 2) with a maximum height of 124 m is examined under a head of 99 m and a 9-point earth- quake. An interstratified block of sandstones and argfllites, which is inclined at an angle of 55-65* to the hori- zontal, serves as the foundation. The modulus of elasticity of the foundation is increased from (20-50) x 10 3 s kg/cm2 in the unloaded zone to (100-150)x 103 kg/cm2in the deep zone. The working values of the shear param- eters in the safe-rock zone are taken as tan 0 = 0.75 and C = 2.5 kg/cm2.Along fault planes.Ordinarily,the design and estimate for a storage dam should provide for the injection of grout under pressure to seal seams joints,and other openings in the bedrock to a depth equal to the reservoir head above the surface of the bedrock. Grouting is usually done with neat cement and water startingwith a ratio fo 1:5. If considerable “take” in any one hole is experienced, the grout mixture is thickened progressively until a ratio of 1:1 is obtained. Admixture,such as sand or day, a re added iflarge voids are encountered. F or small dams ,a single line of grout holes is sufficient o Grouting of rock foundations ordinarily will not be required for detention dams, very small diversion and storage dams,or where preconstruction exploration has demonstrated that there are no openings in the bedrocks.Very often is found to be badly jointed or broken for some depth below its structure.In such instances,a concrete grout cap may be needed to facilitate grouting.Tht grout cap is usually a concrete-filled trench excavated a minium of 3 feet and a maximum of 8 feet in the bedrock ,depengding on conditions. The trench is usually made a minimum width of 3 feet to facilitate construction. ° The grout cap performs several functions:(l)It provides anchorage for the pipe nipple to which the grout pump is connected ;(2)it cuts off seepage in the upper portion of the bedrock which cannot be successfully grouted; and (3)it provides weight so that higher grouting pressure may be used at shallow depth。excavation for the grout cap must be carefully performed so that the rock is not shattered.Typical specifications for the performance of grouting and the excavation for the grout cap are included in appendix G.However, if an extensive grouting program is required in the construction of a dam, consulting adivice should be obtained from an engineer experienced in this type of work.For additional information on the subject of grouting,including the experiences of the bureau of reclamation, theU.S. Corps of Engineers, and the Tennessee Valley Authority ,refer to the American Society of Civil Engineers' papers which comprise the "Symposium on Cement and Clay Grouting of FoundationConcrete cutoff walls were formerly provided even for small dams to intercept seepage along the contact of the embankment with the rock foundation, these walls are expensive and are ordinarily not required for small earthfill dams of the type recommended in this text,provided that care is taken to obtain an intimate contact between the impervious portion of the dam and the abutments。 In unusual cases where the bedrock is very smooth, a cutoff wall may be war r an t e d. All lo s e and overhanging rock must be removed from the abutments and the slopes should be flattened to 1 to 1.Where this is not practicable ,a short section of cutoff concrete wall 5feet high should be provided.If the bedrock is a shale which air slakes ,it may be necessary to excavate several feet into bedrock to remove the surface disintegration just prior to placement of the embankment;otherwise excavation into the bedrockjother than for a grout cap) is seldom required .A simple specifications for construction on a shale foundation subject to slaking is included in appendix G.