Dynamic Characteristics on Composite Foundation with CFG Pile

Transcription

1 J. Civil Eng. Architect. Res. Vol. 1, No., 1, pp Received: June 1, 1; Published: August 5, 1 Journal of Civil Engineering and Architecture Research Dynamic Characteristics on Composite Foundation with CFG Pile Ding Jihui 1, Quan Xiaojuan 1, Du Erxia 1 and Zhao Tuo 1. College of Civil Engineering, Hebei University, Baoding, Hebei, China. Hebei Academy of Building Research, Shijiazhuang, Hebei, China Corresponding author: Ding Jihui (dingjihui@1.com) Abstract: The cement-fly-ash-gravel (CFG) pile composite foundation is designed with. m pile length, 35 mm pile diameter and 1. m pile spacing, and the dynamic characteristics of CFG pile composite foundation and the rules of the dynamic response are studied through the field blasting experiment. The experiment shows that under the same conditions of the source of vibration location and heap load, within the scope of the composite foundation, the peak acceleration of each test points are decreased obviously and the site of the CFG pile composite foundation is good for earthquake, except that the individual site horizontal peak accelerations are less than the vertical. When the blast distance is 7. m and 1. m, under the effect of different loads, first order vibration main frequency are concentrated in 15. Hz-17. Hz and. Hz-5. Hz. With the same blast energy, the source of vibration location, the composite foundation form and the size of the upper load make an effect on the main frequency of composite foundation test points. The vibration main frequency is depending on the soil and the pile property between the source of vibration and test points. When the blast distance is different, the max damping ratio of test point on the soil and the pile are respectively.1 and.59, which is in contrast to the actual law, maybe it is the interaction result of the load, the soil and the pile property between the source of vibration and test point. Key words: CFG pile, composite foundation, field test, peak accelerations, main frequency, damping ratio. 1. Introduction In recent years, because of many times earthquake disaster, the dynamic characteristics of composite foundation were paid attention by the earthquake engineering. The vibration peak acceleration, main frequency and damping ratio are very important parameters of the dynamic characteristics of composite foundation experiments. Qi Jianfeng, Luan Maotian, Yang Qing, Ma Tailei, Yuan Ying [1] through a series of tests on saturated clay, the effect of stepped loading history and coupled cyclic stress on dynamic shear modulus and damping ratio under large strain was examined. Xiaoming Yuan, Rui Sun, Jing Sun, Meng Shangjiu, Shi Zhaoji [] using the natural resonant column test method gives domestic conventional soil type dynamic shear modulus ratio and damping ratio with the average dynamic shear strain change curve, the recommended value and envelope. Wang Weiyu, Zhao Tuo, Ding Jihui, Meng Yanjie [3-5] research dynamic characteristics and the rule of the dynamic response of the single pile composite foundation and nine piles composite foundation through blasting experiments. Ding Jihui, Wang Weiyu, Zhao Tuo, Feng Junhui [-] has designed three kinds of composite foundation based on the standpoint of optimizing the pile: CFG long pile and CFG short pile, CFG long pile and soil-cement pile, and CFG core pile and soil-cement ring pile. They studied the dynamic performance and the rule of the dynamic response of three combined composite foundation. This article focuses on the

2 Dynamic Characteristics on Composite Foundation with CFG Pile 15 composite foundation of CFG pile, through the field Signal acquisition system is G1USB3 data blasting experiments, under the action of blasting load, collection and analysis system which is made in the the dynamic characteristics of the vibration peak institute of engineering mechanics of China acceleration, main frequency and damping ratio on seismological bureau. CFG pile adopts C CFG pile composite foundation are studied, which provides a test basis in order to further study the dynamic characteristics of CFG pile.. Material and Methods.1 Test Site commercial concrete, pile length is. m, diameter is 35 mm, the space of piles is 1. m, area replacement rate is.9. The arrangement of the piles and measuring elements are as shown in Fig Results and Discussion The test adopts blasting as the vibration resource The test site is located in Shijiazhuang Hebei and piezoelectric acceleration sensor picks up province. In the. m depth, the soil layers mainly vibration. G1USB3 data collection and analysis are yellow silt clay, fine sand, middle sand and silt system acquires data and then obtains the acceleration clay. In the. m driving depth, the underwater is curves, for example, as shown Fig.. Taking all the not seen. There is not the harmful geologic action in peaks of the acceleration time history curves and the site. The main parameters of soil layer as shown in getting the peak acceleration curves as shown in Figs. Table 1. and 5. Selecting the modal analysis from the data. Model Test and Scheme of the Site collection and analysis system and getting FFT curves, for example, as shown in Fig. 3, through power The upper load is supplied by pilling concrete block, spectrum obtains main frequency and damping ratio, and each load of the composite foundation is added by as shown in Tables -5. an electric pump-hydraulic jack. The square steel is. m. m as the loading plate. The load has 3.1 Peak Acceleration classes, every class is 5 kpa and the total load is 3 Figs. and 5 are peak acceleration curves when d is kpa, smaller than the characteristic value of bearing 7. m and 1. m on the case of. m earthquake capacity of composite foundation. source depth and 1.5 kg explosive charge. The test adopts blasting as the vibration resource From Figs. and 5, the horizontal peak acceleration and the explosive are buried in the hole and then of test points are smaller than vertical peak backing tamping. The d is the distance between acceleration except for few test points which are out blast point and the edge of composite foundation, and of boundary, and they are decreasing with the is 7. m and 1. m. Explosive embedment depth is increasing of the distance. Out of composite. m, with artificial LuoYang shovel making the hole, foundation, the peak acceleration decreases obviously blasting hole diameter is 15 mm, explosive load 1.5 along with increasing of the load on the test points of kg. The vibration is picked by acceleration sensors. Table 1 Main parameter of soil layer. Name of the Thickness of the Characteristic value of Compression Ultimate shaft Ultimate tip soil layer soil layer/m bearing capacity f ak /kpa modulus E s /MPa resistance q sk /kpa resistance q pk /kpa Planting soil. Yellow silt.5 clay Fine sand Middle sand Silt clay

3 1 Dynamic Characteristics on Composite Foundation with CFG Pile 3 5 a m / s Fig. 1 The arrangement of the piles and measuring elements Hz b 3 a m/s 3 1 ( ) / m/s Hz (a) center point of the Composite foundation; (b) side pile point of the Composite foundation Fig. 3 FFT curves of the ( ). ( ) / m/s - b t / s the soil. In the boundary of composite foundation, with the increasing of load, the peak acceleration decreases, but not sharply. On the same load, the vibration peak accelerations with 1. m distance between earthquake source and the edge of composite foundation are smaller than the vibration peak accelerations with 7. m distance. 3. Frequency t / s (a) center point of the Composite foundation; (b) side pile point of the Composite foundation Fig. The acceleration time history curves. Tables and 3 are main frequency tables when d is 7. m, 1. m from the source of vibration to the edge of composite foundation on the case of. m earthquake source depth and 1.5 kg explosive charge. From Tables and 3, when the blast distance is 7. m, the first order vibration frequency is concentrated in the 15. Hz-17. Hz under the different loads, and the

4 Dynamic Characteristics on Composite Foundation with CFG Pile 17 high order frequency is 3. Hz. When the blast distance is 1. m, the first order vibration frequency is concentrated in the. Hz-5. Hz under the different loads, and the high order frequency is 53. Hz. The main frequency on the horizontal direction is a little bigger than it on the vertical direction. When the blast energy is same, earthquake source, the form of composite foundation and upper load all have effect on the main frequency of test points on the composite foundation. The vibration frequency depends on the soil and pile property between earthquake source and test points. horizontal peak acceleration /m/(s*s) m kpa 7m 1kPa 7m 7kPa vertical peak acceleration /m/(s*s) m kpa 7m 1kPa 7m 7kPa (a) Fig. Peak acceleration curves when d = 7. m. (b) horizontal peak acceleration /m/(s*s) m KPa 1m 1KPa 1m 7KPa vertical peak acceleration /m/(s*s) m KPa 1m 1KPa 1m 7KPa (a) (b) Fig. 5 Peak acceleration curves when d = 1. m. Table Main frequency data when d is 7. m. Main frequency/hz distance/m kpa-7 m 1 kpa-7 m 7 kpa-7 m kpa-7 m 1 kpa-7 m 7 kpa-7 m

5 1 Dynamic Characteristics on Composite Foundation with CFG Pile Table 3 Main frequency data when d is 1. m. Main frequency/hz distance/m kpa-1 m 1 kpa-1 m 7 kpa-1 m kpa-1 m 1 kpa-1 m 7 kpa-1 m Damping Ratio The damping characteristics of structure is represented by damping ratio, according to the dynamic formula, in the free vibration with damping, the adjacent two amplitude decay by exponential curve pattern, the ratio of the two is a constant, namely: 1 a ln n (1) k a n k In which, a n, a n+k are the n th and the (n+k) th peak value on the curve, is the wave curve attenuation coefficient. From Eq. 1, concluded damping ratio in Tables and 5. Tables and 5 are damping ratio tables under the distance is 7. m and 1. m from the source of vibration to the edge of composite foundation on the case of. m earthquake source depth and 1.5 kg explosive charge. From Tables and 5, when the blast distance is 7. m, the damping ratio on the horizontal direction and vertical direction are respectively concentrated in the and under the different loads. When the blast distance is 1. m, the damping ratio on the horizontal direction and vertical direction are respectively concentrated in the and under the different loads. Under the effect of different loads, when the blast distance is different, the max damping ratio of measuring points on the soil is.1, the max damping ratio on the pile is.59, which is in contrast to actual rule, maybe it is the interaction result of the load, the soil and pile property between vibration location and test point. Table Damping ratio data when d is 7. m. Damping ratio distance/m kpa-7 m 1kPa-7 m 7kPa-7 m kpa-7 m 1kPa-7 m 7kPa-7 m Table 5 Damping ratio data when d is 1. m. Damping ratio distance/m kpa-1 m 1kPa-1 m 7kPa-1 m kpa-1 m 1kPa-1 m 7kPa-1 m

6 Dynamic Characteristics on Composite Foundation with CFG Pile 19. Conclusion Through the field test of dynamic characteristics on composite foundation, getting the following conclusions: (1) The horizontal peak accelerations of test points are smaller than vertical peak accelerations except for few test points which are out of boundary, and they are decreasing with the increasing of the distance. Out of composite foundation, the peak acceleration decreases obviously along with increasing of the load on the test points of the soil. In the boundary of composite foundation, with the increasing of load, the peak acceleration decreases, but not sharply. On the same load, the distance between earthquake source and the edge of composite foundation is farther, the vibration peak acceleration is smaller. () When the blast distance is 7. m and 1. m, the first order vibration frequency are respectively concentrated in the 15. Hz-17. Hz and. Hz-5. Hz under the different loads. When the blast energy is same, earthquake source, the form of composite foundation and upper load all have effect on the main frequency of test points on the composite foundation. The vibration frequency depends on the soil and pile property between earthquake source and test points. (3) When the blast energy is same, under the effect of different load and blast distance, the max damping ratio of measuring points on the soil is.1, the max damping ratio on the pile is.59, which is in contrast to actual rule, maybe it is the interaction result of the load, the soil and pile property between vibration location and test point. Acknowledgment This work was supported by The Natural Science Foundation of Hebei Province under Grant (No. 11-E1). Reference [1] Qi Jianfeng, Luan Maotian, Yang Qing, Ma Tailei, Yuan Ying, Dynamic shear modulus and damping ratio of saturated clay, Chinese Journal of Geotechnical Engineering 3 () (in Chinese) [] Yuan Xiaoming, Sun Rui, Sun Jing, Meng Shangjiu, Shi Zhaoji, Laboratory experimental study on dynamic shear modulus ratio and damping ratio of soils, Earthquake Engineering and Engineering Vibration () (in Chinese) [3] Wang Weiyu, Zhao Tuo, Ding Jihui, Influencing factors of dynamic characteristics and response of cement-fly-ash-gravel pile composite foundation, Chinese Journal of Geotechnical Engineering 15 (1) (in Chinese) [] Zhao Tuo, Yang Changmin, Wang Weiyu, Experimental study of dynamic characteristics on composite foundation with CFG pile under blasting load, Highway Traffic Science and Technology (application version) 7 (1) (in Chinese) [5] Wang Weiyu, Zhao Tuo, Meng Yanjie, The numerical analysis of dynamic characteristics of the CFG pile composite foundation under the action of blasting vibration, Engineering Mechanics 9 (1) (in Chinese) [] Ding Jihui, Wang Weiyu, Zhao Tuo, The dynamic characteristic experimental method on the composite foundation with rigid-flexible compound piles, Open Journal of Civil Engineering 3 (13) -93. [7] Ding Jihui, Wang Weiyu, Zhao Tuo, The experimental study on the dynamic characteristics and attenuation law of the composite foundation, IJIRSET 11 (13) [] Ding Jihui, Cao Yanliang, Wang Weiyu, Experimental study of dynamic characteristics on composite foundation with CFG long pile and rammed cement-soil short pile, Open Journal of Civil Engineering (1) 1-1.