1 Introduction

Sichuan–Tibet railway has been included in China western development strategy.Sichuan–Tibet railway is expected to across the Hengduan mountains from the east of Tibet plateau,and this area has the geomorphic features of high altitude and large elevation difference and distributes a large amount of glacial lakes.In the Parlung Zangbo river basin,for example,there are 461 glaciers and 131 glacial lakes of different sizes[1,2].In nearly 40 years,there had eight large-scale debris flow from glacial lake outburst floods(GLOF),blocking and damaging roads from 20 to 270 days.For example,in July 1988,debris flow resulting from GLOF in Midui destroyed nearly 30-km Sichuan–Tibet roads and blocked the route for half a year[3].The lake outbursts pose a catastrophe risk to the Sichuan–Tibet railway coming across the Parlung Zangbo river basin,which is a challenge in China’s railway history[4].Moreover,Parlung Zangbo river basin is located in strong earthquake regions where more than 40,000 earthquakes have been recorded since 1970,and more than 3000 of these earthquakes were greater than Ms3.0,posing a potential threat to the stability of moraine dams[5].In recent years,with the global warming and glacial retreating,moraine-dammed lake disaster has a tendency to increase.Therefore,the moraine-dammed lake outbursts caused by earthquakes have become a special environmental geological hazard to railway route[6].

综合以上4种情况,在最坏情况下是7-点关联着(3,3,7)-面,3面及面上的点最多从7-点拿走的权值为称之为最坏3-面7-点情形。

The seismic action not only directly threatens the stability of the dams,but also causes the water movement of upstream reservoir.Two forces acting on a dam during an earthquake are the seismic inertial force of the dam itself and water pressure.A large quantity of water is forced to act on the dam repeatedly,and thus,the water pressure on the dam is not negligible[7–9].Westergaard first proposed an expression for the hydrodynamic pressure exerted on the vertical upstream face of concrete dam,assuming that the boundary was semi-infinite and the excitation wave was horizontal harmonic wave[10].The following approximate formula was obtained[10]:

where y denotes the water heights,P is the maximum hydrodynamic pressures at height y,h is the reservoir depth,ρ is the unit density of water,khis the seismic acceleration coefficients in the horizontal direction,and g is the acceleration of gravity(9.8 m/s2).The approximate formula provides a convenient way for solving the response of the dam–water interactions.In 1953,Zangar developed an experimental solution for the same problem using an electrical analogue and reported extensive results for a variety of non-vertical upstream faces[11].Based on momentum method and two-dimensional potential flow theory,Chwang solved the hydrodynamic pressure problem with a more general configuration of a dam[12,13].Wang et al.[14]modified Westergaard’s equation considering the influences of the dam height,elasticity,and reservoir bottom condition.Saleh and Madabhushi[15]investigated the effect of dam–foundation interaction on the hydrodynamic pressure response on the dam face under different earthquake waves using the dynamic centrifuge modeling technique.The results generated by these works were more or less equivalent to the results of Westergaard,and thus,the approximate formula has been widely used to calculate the hydrodynamic pressure loads.

Therefore,it is now widely believed that the earthquakeinduced hydrodynamic pressure is mainly affected by parameters such as the peak ground acceleration(PGA)and the initial water depth.In this paper,the conditions of rigid vertical upstream face and flat bottom were simulated to obtain the hydrodynamic pressure.However,in many cases,the moraine-dammed lake is small,where the boundary reflections may be not negligible.Therefore,it is necessary to study whether Westergaard’s formula can be applied to calculate the hydrodynamic pressure in small reservoirs or lakes.

Figure 6 shows the change of hydrodynamic pressure recorded by P1pulsating water pressure sensor.Then,FFT was used to derive the pressure spectrum,and the water fundamental frequency is 0.3325 Hz(Fig.7).It is found that the input seismic excitation frequency is far away from the fundamental frequency,indicating that the resonance did not appear.

2 Simulation experiment

2.1 Experimental setup

Fig.1 A typical illustration of the experimental setup(unit:mm)

The simulation experiments were conducted on a shaking table.The experimental setup is illustrated in Fig.1.The shaking table container was about 3.76 m in length,1.75 m in width,and 1.50 m in height,with a flat bottom,and driven by an electro-hydraulic system.In this experiment,the water container was designed with a dimension of 2.73 m×1.75 m×0.35 m to simulate themorainedammed lake,and the model scale was about 1/100 with the reference of Midui moraine-dammed lake with the area of 300 m×200 m[19,20].And the physical phenomena such as the process of water movement are well recorded by camera in the experiments.On the side wall,the hydrodynamic pressure distribution along the wall was measured with six pulsating water pressure sensors located from the bottom to the top at the heights of 2,8,14,20.5,27.5,and 31.5 cm.The sensors were numbered as P1–P6.A detailed illustration of sensor distribution is shown in Fig.2.

The Westergaard’s method is able to predict the earthquake-induced hydrodynamic pressure caused by Wolong wave in the small lake with reasonable accuracy.In the experiment,the most disadvantage condition of hydrodynamic pressure is considered,i.e.,the side walls are vertical and rigid,and the hydrodynamic pressure at the side may be larger compared to the normal case.As reference to‘‘Specifications for Seismic Design of Hydraulic Structure’’(DL5073-2000),if an inclined upstream face is with a horizontal angle of θ,the hydrodynamic pressure values should be multiplied by θ/90.

2.2 Experimental design

在全球范围内，肠外致病性大肠埃希菌是导致尿路感染、血流感染和脑膜炎的主要原因［20］。肠外致病性大肠埃希菌进入血流后诱发强烈的宿主炎症应答，从而引起败血症，导致血流感染的高发病率和死亡率［21］。大肠埃希菌ST131型被认为是主要的肠外致病性大肠埃希菌［22-23］。本研究结果显示，在血流感染的大肠埃希菌中ST131型别占6.3%，低于国内外的报道［3-7］，提示ST131还未在本地区血流感染中形成大规模流行，可能存在其他引起血流感染的优势克隆型，需进一步检测。

In each test,the input seismic excitation wave was created by the computer control system.When the vibrator receives the signal,the shaking table moves with the triggering wave.In addition,the hydrodynamic pressures are recorded by the water pressure acquisition system.Even after the seismic wave passes by,the acquisition system keeps running until the entire water body becomes stable.The measured hydrodynamic pressures during the earthquakes were calculated by deducting the initial hydrostatic pressure from the total water pressure recorded by the sensors at the corresponding heights.Moreover,each test was repeated twice to reduce the equipment error or human error.

Generally,the predominant period of seismic wave is from 0.15 to 0.5 s,and the frequency ranges from 2 to 6.7 Hz.Therefore,the sinusoidal waves with frequency ranging from 2 to 6 Hz were used to study the characteristics of hydrodynamic pressures.And the seismic wave adopted the real-time records of the Wenchuan Ms 8.0 earthquake on May 12,2008,at Wolong,which exhibits the dominant frequency of 2.35 Hz.Meanwhile,white noise was used as a signal source from shaking table to obtain the water fundamental frequency.Details of the seismic waves and PGAs in experiments are shown in Table 1.The Wolong wave,3 Hz sinusoidal wave,white noise acceleration waveform,and their spectra by fast Fourier transform(FFT)are shown in Figs.3,4,and 5.

3 Experimental results and discussion

3.1 Fluctuation characteristics of hydrodynamic pressure

In addition,the moraine dams are formed by an unconsolidated,poorly sorted rock debrisorhighly heterogeneous mixture of particles[16–18].The pressure loads acting on this type of dams may lead to failure of the dams and become a critical factor causing the dam to break in the earthquake areas[19].In this paper,experiments were conducted to study the characteristics of hydrodynamic pressures caused by sinusoidal waves and Wolong wave on a shaking table,and the results were compared with those by Westergaard’s formula.

Figure 8 shows the process of water movement caused by the 3 Hz sinusoidal wave recorded by video cameras.During the seismic excitation process,water movement was firstly triggered by the side wall motion and then showed a corresponding sinusoidal motion.After the seismic wave passed by,the water waves immediatelystabilized.Then,the changing characteristics of hydrodynamic pressure were further analyzed according to the measured data of pulsating water pressure sensors.

Table 1 Seismic wave types and corresponding PGAs

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Fig.2 Schematic diagram of the pulsating water pressure sensor(unit:mm)

Fig.3 Seismic parameters of the Wolong wave.a Acceleration response curve wave in time domain.b Spectrum of the Wolong wave

Fig.4 Seismic parameters of the 3 Hz sinusoidal wave.a Acceleration response curve in time domain.b Spectrum of the 3 Hz sinusoidal wave

Fig.5 Seismic parameters of white noise.a Acceleration response curve in time domain.b Spectrum of white noise

As observed in Fig.14,the maximum hydrodynamic pressures along the water depth are increased from top to the bottom,and it is also found that the ratio of maximum hydrodynamic pressure to totalhydrostatic pressure approximately grows from 5%to 25%,increasing monotonously with seismic acceleration.

Fig.6 Fluctuation of hydrodynamic pressure due to white noise(P1 0.1g)

3.2 Sinusoidal wave action

The spectrum curves of the measured pressures recorded by P1sensor under the actions of 3 and 6 Hz sinusoidal waves are shown in Fig.11.

As observed in Fig.11,the predominant frequencies of hydrodynamic pressure are 3 and 6 Hz.They are similar to the spectra of the input sinusoidal waves.This indicates that the response of hydrodynamic pressure is determined by the external seismic excitation wave,and the spectra further reveal the synchronization between the input wave and the hydrodynamic pressure response.In the condition of 35 cm water depth,the distribution of the maximum hydrodynamic pressure with different frequencies along the water depth under different PGAs of 0.1g,0.2g,0.3g was analyzed,as shown in Fig.12.

When PGA is 0.1g,the maximum hydrodynamic pressure along the water depth has the same distribution rules.Under the PGAs of 0.2g and 0.3g,the distribution of hydrodynamic pressures with different frequencies along the water depth was basically the same,but slightly different due to the equipment error or human error.It is shown that the amplitudes of hydrodynamic pressure are independent of the seismic frequency frequencies when the input seismic excitation frequencies are much larger than water fundamental frequency.

【实验过程及现象】1.将打气筒连接到充气阀上，快速向瓶内连续打气，使瓶内气压大大增加，在瓶口的塞子将要蹦起前，读取温度计的示数为t1。

Fig.7 Spectrum of hydrodynamic pressure due to white noise wave

Fig.8 Water movement due to 3 Hz sinusoidal wave(0.2g)

Fig.9 Fluctuation of hydrodynamic pressure due to 3 Hz sinusoidal wave(0.2g)

Fig.10 Fluctuation of hydrodynamic pressure due to 6-Hz sinusoidal wave(0.2g)

Comparisons between the experimental hydrodynamic pressures and Westergaard’s values indicate that the experimental values are slightly larger than Westergaard’s equation.For instance,the experimental hydrodynamic pressures recorded at P1sensor under the actions of 2–6 Hz sinusoidal waves were larger than those calculated theoretically by 10%–20%.The difference is attributed to the following reason.The real water tank has the boundary reflection,while the Westergaard’s formula does not include the boundary effect.As a result,the water waves reflected at the side walls will enlarge the hydrodynamic pressures.Therefore,Westergaard’s formula can accurately calculate the hydrodynamic pressure caused by sinusoidal wave in small lakes.

Fig.11 Fourier amplitude spectrum of hydrodynamic pressure due to 3 and 6 Hz sinusoidal waves,respectively

Fig.12 Distribution of the maximum hydrodynamic pressures with different frequencies.a PGA=0.1g,b PGA=0.2g,c PGA=0.3g

3.3 Wolong wave action

Comparison of the measured hydrodynamic pressures and Westergaard’s formula is given in Fig.14.It indicates that generally,the measured hydrodynamic pressures mostly match well with those calculated by the Westergaard’s formula.As discussed earlier,there exists boundary effect,and hence,we can see that the experimental hydrodynamic pressures are higher than those induced in a semi-infinite reservoir.However,with the same maximum excitation acceleration,the input energy generated by the sinusoidal wave is greater than the seismic wave induced.Therefore,the hydrodynamic pressures induced by sinusoidal wave are greater than the values caused by seismic wave.As a result,the test data for hydrodynamic pressures caused by Wolong wave are mostly in good agreement with Westergaard’s formula.Small deviation may be attributed to equipmenterror or human error in measurement.

Figures 9 and 10,respectively,present the hydrodynamic pressures recorded by the P1sensors attached to the wall under the actions of 3 and 6 Hz sinusoidal waves,The hydrodynamic pressure amplitudes were not increasing with time,but in synchronization with input seismic excitation waves.It is observed that the changing process of hydrodynamic pressures can be divided into two stages:(a)For 0＜t＜20 s,the hydrodynamic pressures obviously follow seismic acceleration wave motion,and(b)for 20 s＜t after the seismic wavepasses by,thehydrodynamicpressurereturns simultaneously to zero.The hydrodynamic pressures recorded at other sensors have similar fluctuations.Further,the maximum hydrodynamic pressures under action of different waves were analyzed.

In the experiment,the hydrodynamic pressures caused by real seismic wave(Wolong wave)were analyzed.Figure 13 presents the hydrodynamic pressure recorded by the P1sensor attached to the wall during the Wolong earthquake,together with the 0.2g PGA.Compared with the sinusoidal waves,the pressure caused by Wolong wave displays similar changes,which is always in synchronization with the response of Wolong wave.For further analysis,the maximum hydrodynamic pressures generated at different heights are shown in Fig.14.The hydrodynamic pressures are normalized with the total hydrostatic pressure,and the sensor depths are normalized with reservoir depth.In Fig.14,y denotes the sensor heights,Pmax(y)denotes the maximum hydrodynamic pressures at heights y,h is the reservoir depth,ρ is the unit density of water(1.0 t/m3),and g is the acceleration of gravity(9.8 m/s2).

根据辩证唯物论的基本要求，客观分析我国现阶段农业生产的重要资源条件和现实需求，发现水资源条件、种植资源条件、劳动力资源条件与现有的水资源开发利用方式和经济发展方式已经越来越不相适应，现实的灌溉物质条件和发展需求已经悄然发生了改变，这些先天的物质条件或者改变了的物质条件从来没有像现在这样严重影响着农业生产的发展，进而也极大地影响着灌溉方式的选择，只有客观认识这些影响灌溉的重要物质条件，并以此为基础自觉能动地选择适宜的灌溉方式，才能实现科学的、可持续的发展方式。

翻转课堂要求参与化原则。要求人人有参与创造的机会，激发人人参与的激情，从而做到提高人人参与的能力，使学生在体会和感悟中学习、成长。翻转课堂的情境导入会突破传统课堂的束缚，让每个学生都成为课堂的主导者，成为学习乐园的参与者。这样才能切身实地地让学生充分阅读课本知识，而不是生搬硬套，成为学习机器，以便培养学生自助管理的能力和效率自己掌控学习的节奏，自己成为学习的主导者。

Fig.13 Fluctuation of hydrodynamic pressure due to Wolong wave(0.2g)

Fig.14 Comparison of the maximum hydrodynamic pressures

4 Conclusions

The characteristics of earthquake-induced hydrodynamic pressures were experimentally investigated using Wolong seismic wave and sinusoidal wave.Analysis of the fluctuation process of hydrodynamic pressure and the distribution of the maximum hydrodynamic pressure along the depth found that the water did not show resonance under action of Wolong wave(2.35 Hz)and sinusoidal waves(2–6 Hz).Conclusions are drawn as follows:

1. When the input seismic excitation frequency is far from the fundamental frequency,the hydrodynamic pressure variation significantly followed the seismic acceleration wave motion.And the maximum hydrodynamic pressures were independent of the input seismic excitation frequencies,but have a positive correlation with PGAs.

2.The comparison of the theoretical values and experimental data shows that Westergaard’s equation was slightly lower than the experimental values caused by sinusoidal waves,but in good agreement with the Wolong earthquake-induced hydrodynamic pressure in this small lake.It is indicated that Westergaard’s formula to calculate hydrodynamic pressures caused by real seismic waves in the small lake is not a conservative approach.

一次偶然的机会， 他参加飞碟旅行团， 到达了一个叫做地球的地方， 赫然发现， 那里的人全都是如他一般的残障， 他留下来， 立刻融入地球人的社会， 再也不觉得少了两只眼睛是不方便的事。

3.In current risk analysis,the surge wave caused by earthquake or ice avalanches is the main potential threat to the glacier lake outburst,while the destructive earthquake-induced hydrodynamic pressures directly affect the stability of the moraine dam and are disastrous to human lives and properties along the shore.

综上所述，在“一带一路”背景下，各个东道国制度指标对改善东道国基础设施的中国OFDI的东道国经济增长效应这一问题上都存在单一“门槛值”。想要发挥这部分中国OFDI带给东道国的经济增长效应，各个东道国制度必须越过相应“门槛值”。

Acknowledgements This work is financially supported by the Natural Science Foundation of China under contract No.41571004;National Key Research and Development Program(Grant No.2016YFC0802206);Research and Development Program of Science and Technology ofChina Railway Corporation (GrantNo.2015G002-N).

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License(http://creativecommons.org/licenses/by/4.0/),which permits unrestricted use,distribution,and reproduction in any medium,provided you give appropriate credit to the original author(s)and the source,provide a link to the Creative Commons license,and indicate if changes were made.

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