Vibration Generated Due To Pile Driving In Water And Soil

Abstract Vibration Generated Due To Pile Driving In Water And Soil Samir M. Abdel-Rahman Samy Abdel-Fattah M. A. Helal Associate Professor Assistant Researcher Professor Mechanical & Electrical Research Institute, National Water Research Center, Delta Barrage, P.O. 13621, Egypt. E-mail: samir4@yahoo.com Implementation of construction projects involve various sources of construction vibrations such as pile driving, dynamic compaction, blasting and operating heavy equipment. Accurate and reliable determination of dynamic effects of pile driving are very important for proper design, construction and safety of neighbour structures. These sources generate elastic waves in soil which may adversely affect surrounding buildings. The effect of construction vibrations on surrounding buildings, sensitive devices and people in the urban environment is a significant consideration in obtaining projects approvals from appropriate agencies and authorities. The dynamic effect of construction vibrations on adjacent and remote structures depends on soil deposits at a site and susceptibility ratings of structures. It is important to assess the dynamic effect before the beginning of construction activities and at the time of construction. Therefore monitoring construction vibrations have to be started prior to the beginning of construction works at a site and be continued during construction to provide the safety and serviceability of sound and vulnerable structures. Three different areas were used to study dynamic effect due to pile driving: water, loosy soil and silty soil. Vibration characteristics under different conditions was determined and the best parameters for evaluating construction vibration was defined. Vibration generated from impact hammer machine and vibratory hammer machine is of high dangerous level; however, vibration level decrease with increase distance from the source due to material damping. It was found that vibration associated with pile driving in water is higher than that due to pile driving in soil. Also, the metallic structures are excited easily and dynamically more sensitive than concrete structures due to pile driving. Vibration generated during sheet pile driving is higher than that during drawing sheet piles. The research points out the importance of doing frequency analysis prior to such great projects and works to control and minimize its dynamic effect. 1. Introduction Sources of construction vibrations generate compression, shear and Rayleigh waves[1,2]. Rayleigh waves have the largest practical interest for design engineers because building foundations are placed near the ground surface. In addition, Rayleigh waves contain roughly 7 % of the total vibration energy and become predominant over other wave types at comparatively small distances from the vibration source. For example, pile driving from depths between 4 and 1 m will generate Rayleigh waves within.4 to 3 m of the pile, depending on the propagation velocities of Rayleigh and compression waves [3]. Soil vibrations are mostly vertical near the source of vertical impact loads, but as distance increases, vertical and horizontal soil vibrations become similar in magnitudes, and, for some locations at the ground surface, the amplitude of horizontal vibrations might be up to three times greater than that of vertical vibrations. The proximity of the frequency of horizontal soil vibrations 1

to one of the building's natural frequencies may generate the conditions of resonance in that building. Moreover, vertical ground vibrations can cause dangerous structural settlements [4,5]. Construction works for great engineering projects including sheet piles and concrete pile driving that use heavy impact and vibratory equipment that generate vibration of transient, random and periodic characteristics. These vibrations of high amplitudes cause fatigue and damage of the nearby structures. Field work at site of constructing a Bridge Mouse and a Navigation Lock of Tawfiki Canal on Dammietta Branch at Delta Barrage Area. Sources of construction vibration have effect ranges from serious disturbances of working conditions for sensitive devices and people to visible structural damage. It may harmfully affect surrounding buildings, generate elastic waves that affect surrounding structures as a result of its propagation through the soil. These waves are damage to structures and it may lead to failure. It is important to estimate the dynamic effect before the beginning of construction activities, and during construction period and should be continued until finishing construction works[6]. These waves are transmitted outward from the source of the pile driving and gradually are attenuated with distance. The attenuation occurs because, with increasing distance from the source, a greater and greater mass of the soil must be affected by the given input of energy. The amplitude of a Rayleigh wave, decreases with distance from the wave source according to equation [1]. The movement of the soil particles involves overcoming some frictional resistance, and a portion of the energy is lost in frictional damping. The attenuation of waves, therefore, is due to geometric damping and frictional damping [3]. A = A r r e α ( r r ) where: A is the amplitude of the Rayleigh wave; A is the amplitude of the Rayleigh wave at the source; r is the distance from the source to the point at which A is measured; r is the radius of a spherical source; and is the damping coefficient. Vibration associated with sheet and concrete pile driving works for project of construction a bridge and a navigation lock on Tawfiki Canal in Kanater area and their effects on hydraulic and nearby structures are monitored and recorded during pile driving. Vibration measurements were done at different conditions and different locations including soil area, water area, on the metallic bridge of delta barrage structure, and on delta barrage structure to predict vibration characteristics when moving closer to residential buildings. 2. Vibration Results during Driving in Soil and Water 2.1 Pile Driving in Soil The levels of vibration are measured during pile driving machine works on soil at seventeen locations by distance from (at the source) to 5 meter on 11 locations every 5 meter apart. Vibration was monitored on the old Delta barrage during pile driving to study the effect of pile driving on safety of this historical structure, where this structure was located at 14 m from pile driving machine. The levels of vibration measured in terms of acceleration (mm/sec 2 ). Results of vibration measured, as shown in Table (1), show that the maximum level of vibration in terms of acceleration mm/sec 2 are reached to 7667.12 mm/sec 2 at the pile driving machine, 2765 mm/sec 2 at distance 5 m, 1945 mm/sec 2 at distance 1 m, 1619 mm/sec 2 at distance 15 m, 1465 mm/sec 2 at distance 2 m, 1137 mm/sec 2 at distance 25 m, 93.74 mm/sec 2 at distance 3 m, 622.94 mm/sec 2 at distance 35 m, 594.7 mm/sec 2 at distance 4 m, 358.44 mm/sec 2 at distance 45 m, 257.65 [1] 2

mm/sec 2 at distance 5 m. However, the vibration levels decrease to 38 mm/sec 2 at distance 14 m. From above analysis, the level of vibration is in the danger range until 25 meter from pile driving machine according to Boyle [7]. So, the structures which in the range of 3 meter from the machine pile driving are subjected to failure and damage. Table 1 Vibration levels (mm/sec2) measured at different distances (m) from the pile driving machine in soil medium m 5 m 1 m 15 m 2 m 25 m 3 m 35 m 4 m 45 m 5 m 7667 2765 1945 1619 1465 1137 93 622 594 358 257 6883 2667 1853 1591 1459 952 914 6 582 334 255 6787 2538 1844 155 143 918 691 554 59 325 255 6183 2375 1842 1545 1385 873 651 53 42 321 254 5925 2311 182 1523 122 87 645 493 399 312 253 4758 2268 1719 158 1196 854 636 479 398 39 252 4756 2243 175 1477 146 849 619 479 397 37 251 455 215 1695 1457 116 848 62 46 38 31 247 Vibratory motion due to pile driving consists of two principal sources including mechanism of pile driving and pile driving machine. Mechanism of pile driving depends on weight of the ram and its speed ( 3 blow/min.) and generates transient wave of at.5 Hz measured in all spectra. The.5 Hz frequency is in the seismic range and may coincide with one of the natural frequencies of the nearby structures and cause damage and failure to these structures. On the other hand, pile driving machine generates periodic wave depending on speed ( 15 rpm = 25 Hz) of the machine. Due to these two sources, a complex wave describing a distinctive motion of dominant frequency 24 Hz and its harmonics containing the frequencies of the two sources where the amplitude of vibration increases However, both amplitude and exciting frequencies attenuate by distance from the source, as shown in Figure 1, during pile driving at soft soil. Exciting frequencies are dominant at 24 Hz and its harmonics at high amplitude at the site of pile driving and decays by distance from the source where the level of vibration decreases and exciting frequencies damped completely. 2.2 Pile Driving in Water The level of vibration measured in terms of acceleration (mm/sec 2 ) in the horizontal direction (shear) was obtained to determine the limits for safety of structures. The levels of vibration were measured on three different sites during pile driving water and far from these sites by distances from 1 to 5 meter. Location 1 at a structure on the West bank of Tawfiki canal bridge at distance from 15 to 3 meter from pile driving source, location 2 on Tawfiki canal bridge at distance 1 meter, and locations 3, at a structure in the west side of Tawfiki canal bridge and pile driving machine far from it by distance from 35 to 5 meter. Measurements, as shown in Table 2 show that the maximum level of vibration is reached to 6128 mm/sec 2 at distance 1 m, 3887 mm/sec 2 at distance 15 m, 255 mm/sec 2 at distance 2 m, 1543 mm/sec 2 at distance 25 m, 1151 mm/sec 2 at distance 3 m, 959 mm/sec 2 at distance 35 m, 871.5 mm/sec 2 at distance 4 m, 711 mm/sec 2 at distance 45 m, and 54 mm/sec 2 at distance 5 m. From measurements it is obvious that the effect of concrete pile as driving in water on residential 3

neighbor objects is in the danger range until 3 meter from driving machine according to Boyle [7], and near to danger after 35 meter where it is approach to 1 m/sec 2. So, the structures which in the range of 35 meter from the machine pile driving are subjected to failure and damage. Vibratory motion due to pile driving consists of two principal sources depending on weight of the ram and its speed ( 3 blow/min.) and generating transient wave at.5 Hz. Also, pile driving machine generates periodic wave depending on its speed (25 Hz). A complex wave is formed containing the frequencies of the two sources where the amplitude of vibration increases. From analysis above and as shown in Figure 2, it is clear that the vibration associated with pile driving in water is higher than in soil. This is due to that pile driving in water where the bed of the Tawfiki Canal contains rocks, and stones of high resistance to pile driving leading to high vibration. Vibration generated in the site of pile driving in water is three times that generated in the site of pile driving in soil. On the other hand, damping of vibration was found to be higher in water than in soil. The structures whether hydraulic or residential are dynamically safe up to 35 m from pile driving in water and they are safe up to 25 m from pile driving in soft soil. However, the residential structures those are at distance up to 4 m from pile driving should be monitored carefully and study methods of their need for additional support and foundations. Vibration Characteristics as driving in Soil and Water 7 Acceleration (mm/sec2) 6 5 4 3 2 water Soil 1 1 15 2 25 3 35 4 45 5 Distance (meter) Figure 1 Dynamic analysis at three locations during pile driving in soil Figure2 Comparison between the Level of Vibration during Pile Driving at Soil and Water area Table 2 Vibration levels history (mm/sec2) measured at different distances (m) from the pile driving machine in water medium 1 m 15 m 2 m 25 m 3 m 35 m 4 m 45 m 5 m 6128 3887 255 1543 1151 959 871 711 54 5938 3132 241 1542 182 956 866 632 53 574 2849 235 1541 125 956 863 566 52 5484 2737 1956 1529 981 952 861 562 498 5356 2616 1946 1527 978 949 857 561 497 5337 262 1922 1523 978 946 846 557 495 5255 2585 1915 1519 968. 944 846 556 492 5212 2573 1898 1513 953 936 845 555 483 4

3. Pile Vibration Measured on Metallic and Concrete Structures Measurements were taken in the horizontal and vertical directions in terms of vibration displacement (µm) and vibration acceleration (mm/sec 2 ). Measurements were taken at two locations on the metallic bridge of delta barrage structure locations (1) and on the Delta Barrage structure locations (2). The distance between the source and these locations is 115 meter. Where, location 1 is at upstream of Delta Barrage structure at 11 m from the vibrator machine, location 2 on front of Delta Barrage structure at 125 m from the vibrator machine, location 3 on the metallic Bridge crossing the Delta Barrage structure at 14 m from the vibrator machine, and location 4 on downstream of the Delta Barrage structure. Measurements, as shown in Figure 3, show that the levels of vibration in terms of acceleration were very small and within the safe limits for the structure. However, a peak measurement occurred at location 1 on the metallic bridge of Delta Barrage in both horizontal and vertical directions and reached of value 343mm/sec 2. Also, the levels of vibration in terms of displacement are in range of 6 µm to 2 µm and this levels are within the safe limits for the structure except one measurement occurred at location 1 on the metallic bridge of Delta Barrage structure reaches to 748 µm (danger level) in the vertical direction according to Richart [8] limit for safety of structures, and that is due to another sources in the project area like hydraulic or traffic loads. Finally, from above analysis the levels of vibration due to sheet pile driving in terms of acceleration and displacement are within the safe limits for the Delta Barrage structure which is far from the vibrator by 11 m distance. However, sheet pile driving generate high level of vibrations in terms of displacement, danger to structure according to Richart [8] limit for safety of structures, at location 1 on the metallic bridge of Delta Barrage structure at 14 meter from the vibrator machine. It is concluded that the metallic structures are excited easily and dynamically affected more than concrete structures due to pile driving. 4 Vertical Acceleration (mm/s 2 ) at Delta Barrage Structure and Mettalic Structure 8 Vertical Displacement (um) at Delta Barrage Structure and Mettalic Structure Acceleration (mm/s 2 ) 3 2 1 Displacement (um) 6 4 2 Location 1 (Mettalic Structure) Location 2 (Concrete Structure) Location 1 (Mettalic Structure) Location 2 (Concrete Structure) Figure 3 Overall vibration levels at two locations at the navigation west side Dynamic analysis was done at the Delta Barrage structure at locations 1&2 in terms of rms. acceleration as shown in Figure 4. The results show that the vibration characteristics due to driving at metallic bridge (location 1) is different than that at delta barrage structure (location 2). No clear exciting frequency measured at the delta Barrage structure, where some exciting frequencies of high amplitudes were measured on the metallic bridge in the order of 24 Hz and its harmonics. The.5 Hz exciting frequency is measured more clear on the metallic structure and is danger to these structures. The average level of vibration signal 5 mm/sec 2 at location 1 and is 2 mm/sec 2 at location 2. So, the sheet pile driving works produce periodic vibratory signal which is completely 5

absorbed by the Delta Barrage structure during passing through the medium, however, the metallic structures in the area amplify the vibration signal and induce exciting frequencies of high level. Metallic structure (location 1) Delta barrage structure (location 2) Figure 4 Dynamic analysis at the Delta barrage and Metallic Structure 4. Vibration Measured during Driving and Drawing Sheet piles Measurements were taken in the horizontal and vertical directions in terms of vibration displacement (um), beside the Tawfiki canal bridge during driving and drawing a sheet pile as shown in Figure 5 at four locations while driving a sheet pile, and at three locations while drawing a sheet pile. The distance between each location and the other is 5 meter length. 4.1 In case of driving a sheet pile Measurements were taken in the horizontal direction in terms of displacement vibration (um). Measurements show that the levels of vibration were varied in the range of 815 um to 345 um at 5 meter from vibrator source, in the range of 43 um to 485 um at 1 meter, in the range of 52 um to 196 um at 15 meter, and in the range of 88 um to 141 um at 2 meter. Results of measurements, as shown in Figure 6, show that the level of vibration decreases with increasing the distance from the vibrator source. Also, the level of vibration at the beginning of driving the sheet pile is starting with high amplitude until the half of the sheet pile and then decreases as the sheet pile goes down to the soil. This is due to soil layer type where the top layer is more hardly than the bottom and needs more driving power to penetrate the sheet pile through the soil. Vibration Displacement in the horizontal direction during Driving a sheet pilel at different locations Displacement (um) 4 3 2 1 5 1 15 2 Distance from vibrator source (m) Figure 5 Driving a Sheet Pile Figure 6 Displacement at different locations while driving a sheet pile 6

4.2 In case of drawing a sheet pile Measurements show that the level of vibration were in the range of 462 um to 54 um at 5 meter from the vibrator source, in the range of 124 um to 19 um at 1 meter, and in the range of 133 um to 281 um at 15 meter. Results of measurements, as shown in Figure 7, show that the level of vibration decreases as increasing the distance from the vibrator source. Also, the level of vibration at the beginning of drawing the sheet pile is starting with high amplitude and decreases as the sheet pile goes up from the soil where the resistance of the soil to the movement of the sheet pile decreases. 4.3 Comparison between Driving and Drawing Sheet Piles By making a comparison between driving and drawing a sheet pile, as shown in Figure 8, it is apparent that the level of vibration at driving a sheet pile is higher than the level of vibration at drawing a sheet pile. Finally, Vibration levels measured at the Tawfiki Canal at different locations in terms of displacement (um) during driving a sheet pile show that displacement that produce from the vibrator is in the danger range until 1 meter from the vibrator source because it is reached to 345 um after 5 meter from the vibrator machine, and 485 um after 1 meter from the vibrator machine and it goes to decrease as we go far from the vibration source. Also, Vibration level measured during drawing a sheet pile show that the displacement that produce from the vibrator is reached to 54 um after 5 meter from the vibrator source and it goes to decrease as we far from the vibration source. Finally, the level of vibration is in danger range until 1 meter from the vibrator machine during pile driving a sheet pile and it is in danger range until 5 meter from the vibrator machine during drawing the sheet pile. Vibration level measured during Driving and Drawing the sheet pile at 5 meter from the vibrator s ource Vibration Displacement in the horizontal direction during Drawing a sheet pilel at different locations 35 1 D is p la c e m e n t ( u m ) 3 25 2 15 1 5 Sheet pile driving Sheet pile drawing Displacem ent (um ) 8 6 4 2 5 1 15 Distance from vibrator source (m) Figure 7 Vibration displacement at different locations while drawing a sheet pile Figure 8 Comparison between driving and drawing a sheet pile at one location 7

5. Conclusions Vibration generated from pile driving machines is of high dangerous level; however, vibration level decrease with increase distance from the source due to material damping. Pile driving machines produce exciting frequency in the seismic range and can cause damage and failure to the nearby structures. The vibration associated with pile driving in water is higher than that due to pile driving in hard soil and soft soil. This is due to that pile driving in water, where the bed of the Tawfiki Canal contain rocks, and stones of high resistance to pile driving leading to high vibration. The safe vibration limits for the nearby structures to the pile driving machines are determined as 35 m for concrete pile driving in water and 2 m for concrete pile driving in soil. The steel structures are excited easily and dynamically more sensitive to pile driving works than concrete structures. Vibration generated during sheet pile driving is higher than that during drawing sheet piles. The level of vibration is in danger range until 1 meter during sheet pile driving, where it is in danger range until 5 meter during drawing the sheet pile. 6. References [1] Svinkin M. R., "Analyzing Man-Made Vibrations, Diagnostics and Monitoring", Proc. of the 3rd Int. Conf. on Case Histories in Geotechnical Engineering, Prakash, Editor, Rolla, Missouri, Vol. 1, pp. 663-67, 1993. [2] Svinkin M. R., "Numerical Methods with Experimental Soil Response in Predicting Vibrations from Dynamic Sources", Proc. of the Ninth Int. Conf. of International Association for Computer Methods and Advances in Geo-mechanics, Wuhan, China, J.-X. Yuan, Editor, A.A. Balkema Publishers, Vol. 3, pp. 2263-2268. 1997. [3] Tschebotariff, G. P., "Foundation, Relating and Earth Structures" 2nd ed., McGraw- Hill Book Co., Inc. New York, N. Y., 1973. [4] Barkan, D. D., Dynamics of Foundations and Bases, McGraw Hill Co., New York, 1962. [5] Dowding, C. H "Construction Vibration", Prentice-Hall, Inc., 1996. [6] Abdel-Rahman, S. M., Vibration Associated with Pile Driving and its Effects on Nearby Historical Structures, International Modal analysis Conference (IMAC), Ca, USA, 22. [7] Boyle, S. "The Effect of Piling Operations in the Vicinity of Computing Systems", Ground Engineering, 199, June, 23-27. [8] Richart, F.E., Hall, J.R. and Woods, R.D., Vibrations of Soils and Foundations Prentice- Hall, Inc., Englewood Cliffs, New Jersey, 414 P, 1976. 8