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ABSTRACT: This paper presents the results of a study of the effectiveness of pre-cast wall-piles and different types of barrier for controlling ground vibrations. A method for estimation of vibration reduction by such wall barriers has been developed, based on wave penetration theory.The PC wall-piles barrier was found to be capable of reducing vibration level by 10 to 15dB at a point just behind such a barrier and about 5dB at 10m away from it. As verified through the percent study, the effect of a barrier composed of hollow PC wall-piles to isolate ground vibration is in between that of a rigid barrier such as concrete wall and that of a gas cushion represented by use of an open trench, these latter effects being determined through a theoretical analysis as reported elsewhere. According to the wave penetration theory, a composite barrier such as the one referred to in this paper provides a high performance to isolate vibration even over lower ranges of frequency. Of the single material barriers herein considered the EPS barriers, indicating that the lower the wave impedance ratio of a barrier is, the higher is its performance. INTRODUCTION Ground vibration, arising from the recent advent of high-speed railways and motorways as well as large-scale factory installations and heavy construction machinery, has become a serious problem affecting the peace of mind of the inhabitants, causing substantial damage to buildings, as well as causing problems for precision equipment. A barrier made of hollow PC wall-piles already proved fairly effective to keep at bay ground vibration arising from heavy vehicles running on a high-raised motor way. These still remain, however, a large number of problems yet to be solved regarding the complex mechanism through which a PC wall-piles barrier is capable of isolating ground vibration.
- Research Report > New Finding (0.51)
- Research Report > Experimental Study (0.40)
ABSTRACT: This paper presents an experimental study on natural frequency of a foundation on a layered soil system subjected to dynamic loading. Using a Lazan type mechanical oscillator, model block vibration tests on a footing made up of steel and of size 300ร300ร50mm are conducted. Three different static weights and three different eccentricities are used to simulate different vibrating mass and dynamic force level respectively. Two different types of layered systems (soft layer over stiff layer and stiff layer over soft layer) are considered and in each type thickness of top layer is varied. In total 90 tests are conducted and the effect of position and thickness of layering is investigated. It is observed that the natural frequency of the system decreases due to presence of the soft layer at the top whereas it increases due to presence of stiff layer at the top. It is also observed that presence of a soft layer at top is more dangerous than at depth. Further, it is found that the variation of natural frequency due to layering can be quantified by an equivalent lumped model. Performance of the method is found to be encouraging INTRODUCTION The design of machine foundation involves a systematic application of the principles of soil engineering, soil dynamics and theory of vibration. Since the classical work by Lamb (1904) and subsequently by Reissner (1936), Bycroft (1956), Lysmer and Richart (1966) and Richart et al (1970), the subject of vibratory response of foundations has attracted the attention of several researchers. The state of the art on the subject has since then made significant strides. Methods are now available not only for computing the response of machine foundations resting on the surface of the elastic half space but also for embedded foundations and foundations on piles.
ABSTRACT: On 29/10/1989, Tipaza"s region situated in the west of Algiers, was vibrate shaken by the Chenoua earthquake. The distance between the centre of this earthquake and Algiers, the capital (90 km), wasn"t a to make a damages for the constructions (Casbah, Bab El Oued, Hamma, Tagaraโฆ). Because this one is dating for the colonial era, and haven"t a earthquake design structures. Then determination of zonal effects is one of the essential components of earthquake design prevention, having recourse to macro-zoning. The conventional method of measuring zonal effects experimentally is based on seismic recording. It is admittedly reliable, but it is laborious. We suggest in this paper an original method evaluated, here consisting of recording a few minutes of seismic background noise on a site and establishing the spectral ratio of the horizontal path to the vertical path. It is thus an economical method of mapping resonant frequencies and thereby gaining a better knowledge of seismic risk in sedimentation basins.. INTRODUCTION Earthquakes are all demonstrations of the geodynamics of the planet, probably; those that marked the popular conscience so much their destructive aspects are big. The geological nature of the Maghreb region, that is located in the limit of two plates the African and Eurasian, is tectonically unsteady. This natural phenomenon of plate instability, has been confirmed these last years by the activity of earthquakes, in the cities of Chlef, Tipaza, Constantine (Algeria), Agadir (Morocco), permits indication that a lot of our cities are not free from the seismic risk. It is therefore, necessary, to protect them, while leading studies are carried out, in order to warn of the seismic risk. It is therefore, necessary, to protect them, while leading studies are carried out, in order to warn of the seismic risk.
- Africa > Middle East > Morocco > Souss-Massa Region > Agadir (0.24)
- Africa > Middle East > Algeria > El Oued Province > El Oued (0.24)
- Africa > Middle East > Algeria > Constantine Province > Constantine (0.24)
ABSTRACT: The continuous surface wave system (CSWS) is a non-intrusive geophysical technique used for evaluating subsurface shear wave velocity profiles. It makes use of Rayleigh (surface) waves that propagate within a zone approximately one wavelength in depth. In ground where the stiffness changes with depth, these elastic waves are dispersive in nature, which means that they travel at a velocity that is dependent upon frequency (or wavelength). CSWS is a particularly attractive method of investigation for landfill engineering due to the non-intrusive nature of the method that eliminates many of the health and safety concerns typically associated with conventional borings for geoenvironmental investigations. This paper reports on the application of the CSWS for site characterization of municipal solid waste landfill. It is observed that the shear wave velocity profiles developed using CSWS at three different sites indicate a difference between young and old waste. However, the shear wave velocity in municipal solid waste was found to increase with depth for both young and old waste. The study also showed the ability of the CSWS to determine the cover thickness when the shear stiffness of the cover is significantly greater than that of the underlying waste. INTRODUCTION However, it is inevitable that certain frequencies will be missing from the spectra of these sources, which may result in gaps in the stiffness profile data. This disadvantage of the SASW method may be overcome by replacing the hammers with a frequency controlled vibrator. This is the basis of the CSWS method. This present paper reports on the application of the CSWS for site characterization of municipal solid waste (MSW) landfills. Measurements at landfill sites located in Los Angeles (USA) and Melbourne (Australia) that illustrate fundamental aspects of the shear wave velocity profile of MSW are presented and discussed.
- North America > United States > California (0.29)
- Oceania > Australia > Victoria > Melbourne (0.25)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
ABSTRACT: The present study is focusing on the monitoring of ground motion in order to detect liquefaction. This study tries to use the strong ground motion records for detection of liquefaction. First, amplitude characteristics of strong ground motion records were investigated. Time histories of ratio of vertical ground acceleration to the horizontal one was calculated from response acceleration records at ground surface in liquefied and non-liquefied areas. If the ratio of vertical ground acceleration to the horizontal one is calculated at each time step, the ratio is remarkably great when the horizontal ground acceleration is close to zero instantaneously. Therefore, the ratio was calculated from the maximum accelerations for every 0.3 second in order to avoid the instantaneous great value. Next, frequency characteristics of the response acceleration records were studied. The Fourier spectra and time histories of the predominant frequency of horizontal ground acceleration in liquefied and non-liquefied areas were calculated. Then the average predominant frequency of the strong motion and decrease rate of the predominant frequency was calculated. Finally these indices were verified by using one hundred response acceleration records at ground surface obtained in Japan. INTRODUCTION It is well known that liquefaction is one of the serious causes of damage to buried lifeline facilities. Although the importance of monitoring was recognized in the field of lifeline earthquake engineering, there are few monitoring systems to detect the occurrence of liquefaction. Tokyo gas has conducted the monitoring of liquefaction by using water pressure meters. This method needs much money and time for site investigation and installation of sensors. The present study tries to use the strong ground motion records for detection of liquefaction. Ozaki and Takada (1997) proposed the ratio of Arias intensity of filtered to nonfiltered acceleration time history by using the horizontal accelerations.
ABSTRACT: This paper deals with the principle and measurement of SASW, which is employed to evaluate liquefaction potential. Based on the detail field tests, SASW is successfully applied to evaluate the ground improvement due to dynamic compaction and dry-vibro gravel piles. The relationship between the shear wave velocity Vs and the SPT blow number is also discussed.
INTRODUCTION The spectral analysis of surface wave (SASW) method is a relatively.new seismic method which is currently being used in subsurface exploration and gaining more and more attention from the engineering fratenity. The SASW method is based on analysis of the dispersion characteristic of Rayleigh waves (R-waves) in a nonhomogeneous medium. Dispersion means that the velocity of R-waves is dependent on the frequency or wavelength, therefore, waves of different frequencies or wavelengths will propagate with different velocities. Since the wavelength of R-waves is inversely proportional to the frequency, lower frequency waves penetrate to greater depths than higher frequencies. Thus the analysis of the frequency spectrum will produce valuable information about an underground medium. The SASW method is operated from the ground surface by generating R-waves using a instantaneous source and detecting them by receivers. The source should be able to excite a wide range of frequencies. The receivers are oriented to detect the vertical components of the R-waves. The surface wave, comprises sixty-seven percent of the total propagation energy. Rayleigh wave, in essence, is the superposition of perpendicular component of a longitudinal wave and a transverse wave at the interface. Due to its characteristics of high energy, low propagation velocity (Vr
- Geophysics > Seismic Surveying > Seismic Processing (0.60)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.60)
ABSTRACT: Only a limited number of geotextile-reinforced soil (GRS) structures have been constructed as important permanent structures supporting heavy load, such as bridge abutments and piers, due to their relatively low vertical stiffness. To alleviate this problem, the preloaded and prestressed (PLPS) reinforced soil method has been proposed. To evaluate the seismic stability of PLPS GRS structures, a series of shaking table tests of small models were performed. It is shown that the seismic stability of PLPS GRS structures becomes very high by proper preloading and prestressing. Resonance of the structure to seismic load can be avoided by maintaining a high natural frequency of the structure with a high prestress. A measures to maintain a sufficiently high prestress during strong shaking is presented. INTRODUCTION Geotextile-reinforced soil (GRS) structures have a reputation in a high cost-effectiveness. However, the vertical stiffness of GRS structures could be insufficient to be used as critical permanent structures, such as bridge abutments and piers that allow only small deformation. To alleviate this problem, the preloaded and prestressed (PLPS) method has been proposed (Figure 1: Tatsuoka et al., 1996, Uchimura et al., 1996, 1998). In this construction method, after a full-height of structure is constructed, a large vertical preload is applied to the backfill by means of tie rods fixed to upper and lower reaction blocks. The vertical load is then decreased to a prescribed prestress level before opened to service. The first prototype PLPS GRS structure was constructed as a 2.7 m-high bridge pier for a one-track railway in Kyusyu, Japan (Figure 2). The pier supports two 16.5 m simple beam girders with a dead weight of 390 kN for each. The backfill is a densely compacted well-graded crushed gravel, reinforced with geogrid layers with an average vertical spacing of 15 cm.
- Geology > Geological Subdiscipline > Geomechanics (0.72)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.49)
ABSTRACT: Underground roof rock beams crossed by vertical joints, are analysed numerically. Various joint patterns and joint material compliances, are considered. Their effect, for small deflections, is related to the mechanical response of the roof rock beams; i.e. the joint contact length and extreme strain at the abutments and midspan, the midspan deflection, and the shape of the thrust line. Finally, these values are correlated to the analytical ones which correspond to the simpler voussoir beam idealizations. INTRODUCTION The behaviour of an underground roof composed of stratified, jointed and competent rock has been studied initially by Fayol (1885); he noted experimentally that the lowest stratum of the roof was not loaded by the upper ones. Subsequent researchers, starting with Evans (1941), studied the behaviour of such a single bed roof and provided graphs, tables and algorithms for the prediction of its behaviour. Wright (1974) created a design procedure for the control of layered, bolted or unbolted, underground, undermined roofs, based on finite element and laboratory experiment results. Sterling (1980) captured the salient features of the work of Evans and other researchers and by experimenting on his apparatus provided a coherent picture of the deformation and failure modes of roof rock. This was noted by Brady and Brown (1985), who suggested an explicit account to be taken of the presence and compressibility of cross joints in estimating the elastic modulus. Therefore, it is considered necessary to investigate on the behaviour of such roofs and on the divergence of their response from the pertinent analytic formulae for the idealised model. Evaluation of the response of the various roof beam geometric configurations is achieved with the distinct element code UDECTM (1999), under plane strain conditions. These rock roofs contain vertical joints of varying frequency of occurrence and material compliance.
ABSTRACT: Semi-empirical methods are widely used in the seismic response analysis of pile foundations because the complexity of the problem precludes 3-D dynamic finite element analysis. The most common approach for the analysis of pile foundations is the use of nonlinear Winkler springs and dashpots to simulate the interaction between piles and soil. The properties of these springs are specified by p-y curves. The most widely used curves are those recommended by the American Petroleum Institute. In order to include the effects of inertial interaction with the superstructure, a very simplified foundation-superstructure model is employed in the analysis. This paper evaluates the effectiveness of p-y curves and the simplified foundationsuperstructure model in simulating the response of pile foundations. The p-y curve approach is shown to be potentially unreliable. The simplified model is shown to work very well provided the pile foundations undergo very little rotation of the pile cap and the pile foundation is analyzed using a simplified nonlinear continuum model of the soil-foundation system. INTRODUCTION Seismic soil-structure interaction analysis involving pile foundations is one of the more complex problems in geotechnical earthquake engineering. The analysis involves modelling pile-soil-pile interaction, the effects of the pile cap, nonlinear soil response and inertial interaction with the superstructure. Commercial structural analysis programs can not include the pile foundations directly. Therefore in the seismic analysis of bridges and buildings on pile foundations, various semi-empirical procedures are widely used. Dynamic nonlinear finite element analysis in the time domain using the full 3-dimensional wave equations is not feasible for engineering practice at present because of the time needed for the computations. However, by relaxing some of the boundary conditions associated with a full 3D analysis, it is possible to get reliable solutions for nonlinear response of pile foundations with greatly reduced computational effort.
- North America > United States > California (0.30)
- North America > Canada > British Columbia (0.28)
ABSTRACT: The occurrence of rockfalls from a columnar basalt cliff at the Lal Lal Falls reserve, near Ballarat, Victoria has been estimated using erosion rates and historical data. Erosion rates were calculated from the volume of material removed over the past 3 million years, based on the geomorphological history of the site. Historical data included a rockfall in 1990, which caused the death of two high school students, and another rock topple observed in 1992. A reasonable agreement is found between the volume of material involved in the observed events and the calculated annual erosion rate. In the absence of more reliable data, the method provides a useful estimation of event size and frequency. INTRODUCTION On March 28 1990 two high school students were tragically killed by a rockfall while participating in a physical education excursion at the Lal Lal Falls Reserve. The site is a small recreation reserve about 18 km southeast of the City of Ballarat used for picnics and educational excursions. The main feature of the reserve is a waterfall approximately 35 m high, the upstream migration of which has formed a gorge bordered by steep cliffs along the Lal Lal Creek (Figure 1). The walls of the gorge expose two layers of basalt, both exhibiting well formed columnar jointing. At the time of the accident, the students were participating in an abseiling exercise on the upper part of the valley wall. Recent acceptance of risk assessment techniques in engineering geology and geotechnical appraisals require estimates of the frequency of such events, or likelihood of occurrence of rockfalls to be evaluated. Such estimates are inherently difficult and this paper details a method using the geological and geomorphological history at the site to calculate the erosion rate, which is compared to rockfall event frequency.
- Geology > Geological Subdiscipline > Volcanology (0.98)
- Geology > Rock Type > Igneous Rock > Basalt (0.98)