Seismic Reinforcement Analysis And Evaluation For Small And Medium-sized Earth-rock Dams

Earthquake liquefaction of dam materials is a significant factor to instability of earth-rock dams, and liquefaction evaluation has an important influence on reliability of seismic design and reinforcement of earth-rock dams. At present, a liquefaction evaluation method based on liquefaction test and seismic response analysis is used in design of some important earth-rock dams and the reinforcement of some small and medium-sized earth-rock dams in China. How to determine dynamic parameters of dam materials (including maximum dynamic shear modulus, the attenuation regularity of modulus ratio with dynamic strain and the growth regularity of damping ratio with dynamic strain) and liquefaction resistance are keys to realize liquefaction evaluation. In engineering practice, due to restrictions such as sampling and test apparatus, the maximum dynamic shear modulus and liquefaction resistance of dam materials (especially sands) are difficult to obtain through indoor test. Instead, they are usually estimated by empirical formulas, which are usually functions of parameters from standard penetration test, cone penetration test or site wave velocity test. Empirical formulas based on the standard penetration test value are especially common. However, large discrepancy exists in empirical formulas from different countries or regions, resulting in inconvenience to engineering application. Therefore, it is necessary to further analyze these empirical formulas and exploring their applicability. In addition, China is faced with the arduous task of a large number of small and medium-sized dam seismic reinforcement, but the experience is inadequate. So research on analysis and evaluation of small and medium-sized dam’s seismic reinforcement has certain practical significance.In this paper, existing empirical formulas between maximum dynamic shear modulus and standard penetration test value from oversea, and124empirical formulas between shear wave velocity and standard penetration test value from domestic and international were compared and analyzed. On this basis, the maximum, minimum, and average curve formulas between maximum dynamic shear modulus and standard penetration test value for all soils were given, also the maximum, minimum, and average curve formulas between shear wave velocity and standard penetration test value for all soils, silt, sand, clay were given, to estimate maximum dynamic shear modulus of different types of soils. Then, maximum dynamic shear modulus of materials of a earth-rock dam in Shandong province were calculated respectively using the maximum curve formulas, minimum curve formulas and average curve formulas between maximum dynamic shear modulus and standard penetration test value given above. The three pairs of parameters from calculation above were used as three different cases to conduct the seismic dynamic response analysis of this earth-rock dam, to analyze the sensitivity of dynamic response to different input of maximum dynamic shear modulus value. At the same time, the results were compared with that based on maximum dynamic shear modulus value calculated according to Hardin et al.’s and Seed et al.’s empirical formulas, to analyze the applicability of different empirical formulas. At last, suggestion for use of these empirical formulas was given according to the analysis.In addition, the author used four different empirical formulas based on SPT value, including Youd et al.’s formula for SPT clean-sand base curve, Kiyoshi’s empirical formula, Xie Junfei’s empirical formula and Fu Sheng Cong’s ultimate state anti-liquefaction stress ratio formula, to calculate anti-liquefaction stress ratio of sand at upstream shell of dam and sand at dam foundation for a small and medium-sized earth-rock dam in Shandong province. Then the results were compared and analyzed. Based on the analysis and referring to other engineering practice, result calculated from Kiyoshi’s empirical formula was selected to conduct liquefaction assessment of this dam. Map of the liquefaction safety factor contour for liquefaction area of the dam was given to show the liquefaction analysis result and to provide evidence for dam reinforcement design. Then, based on the summarizing experience in seismic strengthening of earth-rock dam domestic, the author conducted the analysis and assessment of this small and medium-sized dam.The study above provides reference to liquefaction assessment of small and medium-sized earth-rock dams in earthquake and anti-seismic reinforcement assessment and evaluation of small and medium-sized earth-rock dams in China.