Study On Identification Of Pulse-like Ground Motions And Influence On Dynamic Response Of Slopes

Earthquake causes immeasurable loss to lives and properties but not compared to secondary disasters,such as landslides,rockfalls,tsunami that accompany them,which causes significant threat to the economy in general.Earthquakes could be near-fault or far fault depending on the point positions nearness to earthquake epicenter,velocity pulses,and rapture mechanism.And it's been known from research that the near-fault ground motions cause severe damage to the structure due to velocity-pulse,which has made the pulse-like ground motion one of the most earthquake engineering research topics of interest in recent times.Statics and results from research conducted by scholars over the years(both home and abroad)show that slopes are immensely affected by near-fault ground motions,making the study of pulse-like ground motions'effect on slope stability of practical significance.Because of the above analysis,the main content of this paper is to study the identification and extraction of pulse-like ground motion and its characteristics and study the impact of pulse-like ground motion on the dynamic response of slope.The main contents are as follows:(1)There are existing methods for identifying and extracting pulses.Due to some of these methods'weak adaptability to pulse waveform,and incomplete consideration in selecting pulse characteristic parameters,this paper proposes an improved method to extract velocity pulse.For the determination of pulse period,considering that different definition methods are suitable for different period segments.The S_v method,which is suitable for the short period,and the S_v×S_d method,which is suitable for the medium and long period,are used to determine the pulse period at the same time.The final pulse period will be the most reasonable value of these two alternatives.For determining pulse amplitude,the Peak Point Method and the formula calculation method are used to define two alternative items.To determine the time offset,the“Mean Area Method”is proposed to solve the problem.The calculation formula of pulse index is determined to identify the pulse.On this basis,the recognition and extraction of multiple pulses are realized,which reduces the possibility of missing pulse-type ground motion.(2)Based on the ground motion data of Hualian earthquake,the directionality of impulse characteristics is studied,the difference of response spectrum between impulse type ground motion and non-impulse type ground motion is compared and analyzed.And the difference of duration of impulse type ground motion in NS and EW direction and its relationship with fault distance is studied.The results show that:The pulse characteristics of the ground motion recorded by the same station are not only in one direction,but the intensity of the pulse characteristics in each direction is also different.Pulse-like ground motion can cause larger acceleration,velocity,and displacement responses of the structure in the medium and long period.The duration of NS and EW direction components of ground motion has little difference.The duration of pulse-like ground motion is shorter than that of non-pulse ground motion on the whole,which indicates that the energy of pulse-like ground motion is more concentrated than that of non-pulse ground motion.The duration of NS and EW direction ground motion components increases gradually with the increase of fault distance.(3)The influence of the original wave,impulse wave,and the residual wave of pulse-like ground motion on the dynamic response of slopes is studied.The impact of different types of pulse-like ground motion on the dynamic response of slopes is compared,and the relation between the relative energy of pulse and the maximum horizontal displacement of the slope is studied.The results show that:When pulse period is close to slope natural vibration period,under the effect of the pulse wave,the dynamic response of the slope is similar to the original wave,it shows that the pulse composition in ground motion has played a significant role,and by comparing the residual wave under the action of the pulse wave and the maximum horizontal displacement of the slope,found that the pulse wave on the slope displacement response is far greater than the influence of residual wave,which shows that compared with non-pulse ground motion,the ground motion with pulse characteristics has a more significant effect on the displacement response of the slope.In type A pulse-like ground motion(two-way velocity pulse)and type B pulse-like ground motion(one-way velocity pulse),under the action of the slope,PGA amplification ratio change rules are similar,but the type B pulse-like ground motion is higher than that of type A,and on the PGV magnification ratio,two types of ground motion have no obvious difference.When the average pulse period is close to the natural vibration period of the slope,the correlation between the maximum horizontal displacement and the pulse relative energy is strong.The maximum horizontal displacement of the slope increases with the increase of the pulse relative energy.