Figure 90.-Layout of structural behavior instruments in dam-Reading station and conduit details. INSTALLA @LEN CANYON DAM LAYOUT DE STRUCTURAL BEHAVIOR NAIBU READING STATION AND CONDUIT DETAILS. The jointmeters detect the condition of joint opening until the joints are grouted, and after that time serve as the means of determining the effectiveness of the grouted joint. The strain meter installation ranks first in numbers and importance. On 16 radial lines through the dam, groups of strain meters in three-dimensional configuration are embedded in the mass concrete to measure volume changes from which the stresses can be computed. The strain meters also measure concrete temperature at their locations. The groups of strain meters on the radial lines are installed near the base of the maximum section of the dam and in arch elements at three elevations in the dam. Each group of strain meters comprises 12 instruments installed as a cluster. Each radial line of strain meter groups contains one pair of "no-stress" strain meters. The patterns of radial lines are generally on the centerlines of blocks and were selected to define a system of horizontal and vertical planes that represent approximate arch and cantilever elements on which stress information is obtained by the trial-load design analysis of the dam. Stress information at a number of arch-cantilever intersections common to both methods of investigation is thus available. Cantilever and arch stresses are determined at the base of the maximum section where maximum cantilever stresses are to be expected. Similarly the stresses are determined at sections in three arches which are about uniformly spaced through approximately the lower two-thirds of the dam and at elevations where the distributions of arch and cantilever stresses are desired. To obtain stress distribution in each of the sections, the groups of strain meters are placed at six locations between the upstream and downstream faces of the dam at the base of the maximum section in block 12 at elevation 3060; in blocks 7, 12, and 18 at elevation 3165; and in blocks 4, 7, 12, 18, and 21 at elevation 3315. At elevation 3450 six groups are installed, similarly, in each of blocks 3, 22, and 24; five groups in each of blocks 6 and 14; and three groups in each of blocks 11 and 19. Where six groups are installed, three are upstream and three downstream from the longitudinal joint. Where five groups are installed, three are upstream and two downstream from the longitudinal joint. Where three groups are installed, there is no longitudinal joint. The strain meter groups record length changes which are used in the computation of true structural stresses. In the stress analysis, data are required regarding the volume changes in the concrete that take place in the absence of stress. "No-stress" strain meters are installed to supply this information. These strain meters are installed under a free surface in the interior of the dam so that the instruments are not affected by vertical loads. Since temperature change is one of the most important contributory factors to the internal stresses in an arch dam, an array of resistance thermometers is installed in a grid pattern near the maximum section, block 12 below elevation 3480, to record this factor. A similar grid pattern of resistance thermometers is installed in block 11 between elevations 3420 and 3600, and in block 22 at elevations 3540 and 3600. In addition, resistance thermometers spaced at equal intervals from the base to the top of the dam at the upstream face of the dam in blocks 11 and 12 record lake temperatures at various depths. Provision for measurement of arch stresses in two arch elements at elevation 3502.5 and elevation 3675 was made by installing stress meters at those elevations. Six stress meters were installed on the centerlines of each of blocks 2, 4, 22, and 25, and three on the centerlines of each of blocks 7, 12, and 18, all at elevation 3502.5. Three stress meters were installed on the centerlines of each of blocks 2, 4, 7, 12, 18, 22, and 25 at elevation 3675. An array of six stress meters is installed in conjunction with a strain meter group at an interior location in the mass concrete of block 12, elevation 3165. Pairs of the stress meters are placed on the same three major orthogonal axes as strain meters to form a three-dimensional configuration for investigating the strain-stress relation at a location in mass concrete. At elevations 3165 and 3450, block 12, four thermometers are placed at varying distances from penstock 5 to determine the temperature gradient in the concrete due to the temperature of water flowing through the penstock. Similar installations of four thermometers each at elevation 3360, block 12, and elevation 3540, block 22, near the downstream face of the dam, are to determine the temperature gradients at varying distances beneath the concrete surface due to air temperature and solar radiated heat. Trios of mutually perpendicular strain meters are installed near the upstream and downstream faces of the dam at elevation 3675 in blocks 4, 12, and 22, to determine strain gradients near the surfaces. In conjunction with the installations of strain meter groups and stress meter arrays at the various locations throughout the dam, jointmeters are placed on the radial contraction joints, and on the longitudinal contraction joints where they exist, at the same elevations as the strain meters and the stress meters. Two jointmeters were installed across and near the upper ends of the longitudinal contraction joints in each of blocks 2, 4, 12, 18, and 25. Three mutually perpendicular strain meters were mounted on the rock of the top and downstream wall of the control cable tunnel in the west canyon wall downstream from the right abutment of the dam at approximately elevation 3325. Those strain meters are parallel to and across the "A" joint in the rock formation. The strain meters are for the purpose of measuring relative movements of the rock on opposite sides of the "A" joint. Strain meters, stress meters, jointmeters, and deformation meters are all of the unbonded resistance wire type and are all modifications of the basic Carlson strain meter. Those meters are read electrically, using special wheatstone bridge test sets, from reading stations, most of which are in the galleries of the dam. Embedded insulated electrical cables extend from the meters to terminations at the reading stations. Embedded resistance thermometers are likewise connected to similar terminations and are read electrically from the same reading stations. (b) Observation of Dam Movement by Surveying Methods.-The two types of precise surveying measurements used for measuring the structural deformation of the dam comprise: (1) a system for horizontal angular measurements made by a first order theodolite from six piers located downstream from the dam and from two auxiliary piers on the dam to targets on the dam and on the abutments, and to three deformation points in wells near the toe of the dam; and (2) measurements of deflection from five plumblines installed in formed wells that extend from near the foundation to the top of the dam. Measurements from the targets and measurements from the plumblines are correlated. A periodic check is made over the deformation points and the system of targets which are installed in a grid pattern at 68 points on the downstream face of the dam and at 17 points on the abutments. The grid pattern of targets defines arch and cantilever elements of the dam. Periodic observations of the targets and deformation points are made from the three pairs of piers which are located at three elevations on the abutments and downstream from the dam. An additional pair of theodolite piers located farther downstream complete quadrilaterals with the six piers from which measurements to the targets are made. The layout of the system of targets and deformation points, and the layout of the system of piers, are shown on figures 92 and 93, respectively. Using each pair of theodolite piers, accurate angular measurements are made between each target on the downstream face of the dam and the opposite theodolite pier. The auxiliary theodolite piers on the toe of the dam are used to make measurements on the targets on the abutments. All of these measurements are related by triangulation to measured baselines located on the abutments downstream of the dam and to computed baselines between pairs of piers. Differences between the successively measured locations of each target furnish the path of the target as it moves due to the deformation of the dam. When the paths of the targets are projected to the coordinate system for the dam, they may be resolved into components of deflection that are radial and tangential to the axis of the dam. Measured angular and linear data are recorded on a series of appropriate data sheets. (c) Piumblines. -Measurements of a nature similar to those obtained from the surveying measurements method are the measurements of deflection that are obtained from the five plumblines installed in the dam. The plumblines are installed in 12-inch-diameter formed vertical wells in blocks 4, 7, 12, 18, and 21, as shown on figure 84. Reading stations in the galleries are provided on the lower end of each plumbline near the foundation, and at intermediate elevations, as shown on figure 94. Each plumbline consists of a single strand of 0.030-inch-diameter, stainless steel wire suspended from an aluminum spider and stainless steel holding chuck in an airtight enclosure below the roadway and at the upper end of the line. The airtight enclosures are accessible through watertight manhole covers. Each plumbline supports a 26-pound cylindrical weight at the bottom. At the lowest reading station on each plumbline, a container of oil is provided for damping vibrations of the suspended mass. At the reading stations, doorframes are set in the concrete of the gallery wall and doors seating against sponge rubber seals are provided as closers. At each reading station on each plumbline, an anchor-plate assembly is installed for supporting a portable measuring apparatus. The anchor-plate assembly is positioned so that the upstream and downstream movement, as well as the cross stream movement, of the plumbline is measured from two positions, one position normal to and the other parallel to the axis of the dam. Measurements are made using a measuring apparatus which consists of a |