OHN10110501353
Trench Barriers to Protection of Structures under Dynamic Loadings-1
Hassan Negahdar
11-Postgraduate student, Department of Soil Mechanics, Basement and Foundations, National Research University Moscow State University of Civil Engineering (MGSU)
Abstract
This study presents in detail numerical modeling nonlinear response of soil in model that has been conducted to investigate the protective performance of both open trench and in-filled trench as well as to examine the influences of wall geometry and location from the vibratory source and structure on the isolation efficiency. Also the results of the numerical investigations are analyzed and interpreted to provide recommendations for implementation in design. It is seen from results that in the range distance of 5 to50m after structure, in open trenches curves of reduction displacements ratio have inclined as expected, but for in-filled barriers these curves have declined.
Keywords: Vibration Reduction, Wave Barrier, Soil Response, Wave Propagation.
1. Introduction
One of the most effective methods that have been sued for protection of structure from surface wave is known as wave barrier. In three past decades an extensive research have been carried out by many researchers also the Russian scientists to investigation the efficiency of screening barriers of surface waves energy in soil [1- 4].
In this study a 2D finite difference element model is developed by software package FLAC in order to simulate the efficiency of open and in-filled trench barriers against surface waves with presence of structures and with assuming strain-hardening constitutive model for soil. In the finite difference element analysis of geotechnical problems, the choice of an appropriate constitutive model may have a significant influence on the numerical results. The constitutive model should be able to capture the main features of the mechanical behavior of barriers under complex states of stress. In this contribution for numerical and analytical methods, based on standard some available tests, general parameters have been developed for determination of strain- hardening constitutive parameters.
2. State of research
The dynamic properties of soil materials have been used in tests were found as be mentioned in ref.
[7](see table.1). The properties of concrete and structure have been assumed linear and in elastic models and soil material have been assumed non-linear. All geometrical parameters that have been used in model are shown in ref. [5] (see fig.1 and table 2).
The developed 2D finite difference element models were studied by comparing the achieved results from analysis models with the strain-hardening behavior for soil in terms of attenuation amplitude of displacement on surface ground (Ar) (see Eq.1 ref.[5]).
An important point that must be mentioned that the most researches has been focused on effectiveness barriers with presences no structure and in elastic behavior for soils under sinusoidal and regular excitation dynamic loadings. But in this study we have studied effects of structure and nonlinear behavior of soils on effectiveness barriers under impulse loading.
3. Result
Figure 1a, b, c show the calculated reduction ratios, Ar, for the cases of open and in-filled barriers with presence of structure (X=3.0, 8.0 and 16.0m, D=10m, W= 0.5m and L=3m). As can be seen from figures, for all type of barriers the recorded amplitude ratios of displacement have been reduced and follow the expected trends. In the distance from barrier up to structure and also along the foundation of structure, the amount of ratio (Ar) have been increased, but barriers have good results to attenuation wave energy in terms of displacement of soil particles, in overall.
a
b
c
Figure 1: Calculated amplitude horizontal displacement reduction ratio, depth of trench, 10m, W=50cm and L=3m. a) for exciting at first location, 3.0m, b) for exciting at second location, 8.0m, c)
for exciting at third location, 16.0m.
It can be seen from fig.1 that in the range distance of 5 to10m after structure, in open trenches curves of displacements ratio have inclined as expected, but in-filled ones the curves of reduction ratios have been declined. Also in all type of barriers with considered condition, the amplitude ratio (Ar) under foundation of structure has increased significantly. So it can be concluded that the presence of structure reduce barriers efficiency.
It is be pointed that at the measuring point located 70.0m from source of disturbance, the attenuated displacement amplitude is negligible. Therefore, the analysis of barrier effectiveness can be limited to a distance 70.0 m from the source, as the amplitudes at larger distances are negligible, even without any wave barrier.
The influence of barrier width will be ignored in this study since the proposed width to construct type of open and in-filled trench barriers system is 0.5m. Therefore, the barrier performance will be assessed according to its depth and various form of barrier, while source-barrier-structure distance is constant.
Figures 2a,b,c,d show the reduction ratios of soil displacements for the four depths of trench barriers (D=5, 10, 15 and 20 m.) in open and in-filled situations. The structure located at distance 25m of the right- hand of trench (L=25m.), and disturbance source located within a distance of 8m from left-hand of trench (X=8.0m.). As it can be noted from the figures that the barriers with various depths have different efficiency in reduction energy of surface waves under impulse loadings with presence of structure, and also be seen that the amplitude reduction ratio for various depths of barriers changes randomly. This may be attributed to three reasons: first, the structure vibration under dynamic loading can affect the vibration of particle soils on earth surface; second, the reflected waves at the soil-barrier interfaces, which pass beneath the barrier, are in-phase or out-of-phase; third, the vibration amplitudes are very negligible even without the barrier, and any variation in the response represents a large change in the ratio.
One behavior that was documented by Woods (1968) in his experimental study on open trenches, Baker (1994) in his experimental on in-filled trenches and by Beskos (1986) in his study of sheet pile barriers as vibration isolators[6,7]. They noted that the distance to the principal minima decreases as the barrier depth
a
b
c
d
Figure 2: Calculated amplitude reduction ratio for a trench located at the second location (X=8.0m), a) open trench, b) in-filled concrete trench, c) open trench and surrounded by concrete wall (0.5m),
d) in-filled concrete trench and surrounded by concrete wall (0.5m)
4. Conclusion
In conclusion, this current study aimed to provide a few general guidelines for the design of vibration isolation measures by means of trench-barriers with presence of structures in reality conditions. Based on achieved reduction in soil displacements on ground surface under impulse loading, the wave barriers protective effectiveness was evaluated. Obtained results can be summarized and distilled as below:
(1) For all type of assumed barriers, it can be seen that in three loading location, attenuation curve of soil displacement reduced and follow the expected trends in horizontal direction on ground surface (Ar less than 1). From barrier up to structure and along foundation of structure this ratio has been increased, but barriers in the presence of structure have good results in attenuation wave energy in terms of displacement.
(2) With assumed conditions, in all type of barriers in especially open ones, beneath the structure the amplitude ratio of horizontal displacement soil, Ar, has increased significantly and the maximum amount of Ar be achieved under foundation (after barrier). It means that with using open trenches as barriers the presence of structure after trench reduce barrier efficiency.
(3) It has been observed that the barriers with various depths have different efficiency in reduction energy of surface waves under impulse loadings with presence of structure; this may be attributed to some reasons.
(4) The results show clear minima immediately behind the barrier resulting in having a quiet area; this area can be mentioned as a region for minimum displacements after barrier.
5. References
1. Musayev V.K., Kurancov V.A. (2008)
, “
Development of a method to calculate the constructions of a burial structure under internal explosive wave influences”. Bulletin of Russian University of friendship of peoples. A series of problems of complex safety. no. 1. pp. 75–76.2. Musayev V.K., Popov A.A., Sitnik VT, Fedorov A.L. (2008), “The problems of safety management of complex systems”. Proceedings of the XVI International Conference, RGTU, pp. 236–240.
3. Musayev V.K. (2009), “Security management structures shallow burial under external explosive effects”. Don State Agrarian University "scientific conference, safety and ecology of technological processes and production. pp. 116–120.
4. Musaev V.K. (2009), “A systematic approach to the design and construction of means of protection of the environment”.The Journal of Integrated Security. no. 1. pp. 103–104.
5. Orekhov V. V., Negahdar Kh. (2013), “Investigation some aspects of trench barriers to reducing energy of surface waves in soils”. Journal of MGSU. no. 3, pp. 98-104.
6. Woods RD. (1986), “Screening of Surface Waves in Soil”. Journal of Soil Mechanics and Foundation Engineering (ASCE), no. 94(SM4), pp, 951-979.
7. Beskos D.E., Dasgupta, G. and Vardoulakis, I.G. (1986), “Vibration Isolation Using Open or Filled Trenches”. Part1:
Computational Mechanics. no. 1, pp. 43-63.
