Maximum permissible indices of the safe operation of hydraulic structures

Abstract

Hydrotechnical construction in recent years has been characterized by complex natural conditions of operation of the structures and an increase of the height of dams and storage capacities of reservoirs.These circumstances, just as the increase in the number of hydrostations and increasing wear of earlier constructed structures, are causing an increase of the requirements imposed on their safety.Problems of a theoretical evaluation of the quantitative indices of reliability of hydraulic structures and especially their life, as is known, still do not have a satisfactory solution. Attempts to use the theory of reliability of machines, mechanisms, and other massproduced devices for determining the probability of failure of the structure run into considerable difficulties related to the individual characteristics of each structure and its operating conditions. Therefore on-site observations are presently regarded as the main means of ensuring safe operation of structures.We will examine below one of the aspects of this problem --the direct use of the readings of monitoring and measuring equipment (MME) for timely detection and assessment of dangerous phenomena and processes during operation of structures and their foundations related to possible redistribution of loads, changes in the characteristics of the strength of materials, failure of individual elements, etc. Such phenomena and processes can lead to an emergency situation, in which case the MME will record the immediate progressive changes in the operating indices of the structure [i].In conformity with the construction standards and operating regulations [2, 3,4], the conduction of on-site observations should be organized on all hydraulic structures for evaluation of the state of the "structure--foundation" system, timely detection of defects, prevention of accidents, and improvement of the operating conditions.In this case the observations for structures of the I, II, and III classes should be carried out by means of the MME, and visual observations are sufficient for structures of class IV. Monitoring observations of deformations, settlements, opening of joints, seepage force and discharges, stresses, etc., should be conducted on the structures.Prompt evaluation of the state of the structure from the results of these measurements encounters considerable difficulties, especially on operating structures, owing to the limited number or even absence of qualified hydraulic engineers among the operating personnel.In connection with this it is considered necessary to determine for each structure the maximum permissible or "critical" values of the physical indices so that on comparing them with the readings of the MME the state of the structure can be promptly evaluated.This requirement is given in a number of departmental directives and in individual new standards (e.g., [5]), but its fulfillment runs into considerable difficulties owing to the absence in previously published Construction Specifications and Regulations (SNIP) of instructions concerning the method ...

Criteria for dam safety

“…The following indices are mainly monitored [4,5]: movements and characteristics of cracks in the body and foundation of the dam and in abutment zones, and also in the sides of the reservoir and elements of the outlet works; stresses (including pore pressure) in structural elements of the dam, foundation, and abutment zones, as well as temperature gradients; parameters of the dynamic response of the dam (amplitude, frequency, and duration of oscillations, dynamic stresses of the soil, and pore pressure); seepage discharge in various sections of the dam and foundation, position of the line of seepage, gradients of the head in cutoff elements of the body of the dam and foundation, seepage velocity in cracks of the foundation; characteristics of concentrated seats of seepage (discharge, presence of piping and zones of boiling of the soil, color and temperature of the water, area of wetting on the slopes and in transition sections of earth dams); characteristics of the slide zones in abutments with the canyon walls on the slopes of earth dams, in the upper and lower pools, at the inlet and outlet of outlet works (volume, displacement, characteristics of splitting cracks, or tilt of vertical structural elements and buckling of long horizontal elements); characteristics of the reservoir regime (level, unfilled volume, rate of inflow and outflow of water, rate of variation of the level, wind-wave effects); characteristics of the state and performance of the outlet work, gate equipment, revetments of the slopes, drainage devices, graded filters, and transition sections; corrosion, thawing, and abrasion of concrete.…”

Increase of the effectiveness of safety control of hydraulic structures under pressure

“…In addition to the calculated values, it was suggested in individual cases, when this seems possible, to establish also higher critical values of the indices, on reaching which the margins of stability and strength become lower than the standard ones, the probability of failure is close to i, but the structure has still not reached the limit state [4]. In this case the structure will be in a state requiring taking urgent measures on reinforcement or partial unloading of the structure (a decrease of the water level in the reservoir).…”