www.seipub.org/ce Construction Engineering Volume 4, 2016 doi: 10.14355/ce.2016.04.005
The Influence Analysis of Pile‐driver to Embankment Piles Zhou Ziyan1, Zhou Qi2, Yuan Yulu3, Li Qian3, Zhou Xingde3† 1. Wentian College, Hohai University, Maanshan 243031, PR China; 2. Zhaoqing University, Zhaoqing, 526061, PR China; 3. College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, PR China Email: Xingdezhou@hhu.edu.cn
†
Abstract Aimed at the piles deformation produced by the weight of pile‐driver, both bearing capacity and line‐type of joint‐method‐pile are studied by combining finite element with experiment data. We can acquire by simulated analysis: the line‐type of pile is closely related to corresponding soils properties, and the bigger deformation of pile is located at soft soil layers; the more closer of the distance between pile and pile‐driver, the smaller of pile bearing capacity; related to vertical pile, the maximally reducing ratio of bearing capacity of deformed pile is 32.4 percent. In the paper, a 4.2m lower limit of horizontal distance between pile and pile driver is suggested in order to increase the pile bearing capacity. Key words Joint‐method‐pile; Pile‐driver; Bearing Capacity; Line‐type
Introduction With the rapid development of expressway in our country, the research on composite foundation has become popular, and many studies have been developed, such as analytical solution for consolidation of composite ground with impervious pile[1], correction about settlement calculation method of CFG pile composite foundation[2], bearing behavior of column‐soil‐cushion mutual action in composite foundation with rammed cement‐soil column[3], etc. Most of the studies are based on the assumption of vertical piles, few of them are based on the inclined pile. The inclined pile may be set [4‐5] for some special purposes. The inclination of the pile should be reduced under normal circumstances to avoid influencing the bearing capacity of composite foundation. There are still less studies on the related filed, and relatively, bearing properties analysis is studied only according to the ideal inclination [6‐7], and does not take into account the actual deformation of pile body. Embankment pile is a kind of flexible pile. The age of concrete is short, the deformation module is small, and the soft soil is elastic‐plastic material. Because of this, the shape of the pile is a curve, and its line‐type and soil properties are closely related to the weight of the pile‐driver. For a particular soil, pile‐driver has a great influence on the line‐type of the pile, because that these devices are usually of more than 20t, and are close to the pile. Age is very important for the concrete properties. The existing studies emphasize particularly on the research on the later period [8‐9]. For the early age, Yang put forward the change model of the compressive strength and modulus of elasticity [10]. Based on the practical engineering, this paper takes the new embankment pile ‐ joint method that proposed by the author as an object, and studies the influence on the line‐type and the bearing capacity from the pile‐driver by combining with the experiment on the bearing capacity of the pile [11]. Change Model of the Concrete Early-age Elastic Modulus The change model of the concrete early‐age elastic modulus can be fitted according to the experimental date [10], and the model is as following:
0.034t 0.028 [1 (C 40)( 0.01)]Ec (1) 0.07 0.0315t t Where t is the age and C is the concrete strength grade. Assuming that 0 t 28 and 30 C 60 . Assuming Ec E
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as the elastic modulus of concrete when t=28, we get
Ec
1 105 (2) 2.2 34.7 / f cu ,k
Here f cu , k is the compressive strength of concrete when t=28. f cu , k =34.26 MPa, 45.12MPa, 55.33MPa and 65.28MPa when C=30, 40, 50 and 60. In this paper, C=30, t=1 and Ec =8.30 MPa. Simulation Analysis This paper takes Anhui Chao‐Wu expressway engineering embankment pile as object, and the parameters can be found in Table 1. The pile length is 7m and the pile diameter is 0.4m.The pile spacing is 1.5m and the specific gravity is 25kN/m. The elastic module is 8.30MPa while pile driving, and is 15GPa when it works steadily. The Poisson ratio is 0.167. The pile‐driver’s self‐weight is 24.5t, and Fig.1 shows the interaction site of the piling machine and time‐history curve of self‐ weight. TABLE 1 PARAMETERS OF THE FOUNDATION SOIL
Soil
Soil thickness(m)
1
1.20
2
Name of soil
γ (kN/m3)
Φ (°)
c (KPa)
E (MPa)
μ
Mild clay
17.70
19.60
10.00
2.94
0.30
3.40
Silt clay
17.40
12.30
8.20
1.45
0.40
3
4.70
Mild clay
18.20
27.10
25.00
4.45
0.30
4
6.50
Clay
18.30
29.20
34.60
8.34
0.30
FIG.1 THE INTERACTION SITE OF THE PILING MACHINE AND TIME‐HISTORY CURVE OF SELF‐WEIGHT
FIG.2 FINITE ELEMENT MESHING FIG.3 THE HORIZONTAL DISPLACEMENT NEPHOGRAM OF EACH PILE AT THE END OF PILE DRIVING
ABAQUS is used for simulation and finite element meshing can be seen from Fig.2. There are 14168 soil elements and 1440 pile elements. The calculation is divided into two steps. Firstly, simulating the time‐history curve of pile‐ driver’s self‐weight by assuming that step size is 0.1. Secondly, simulating the ultimate bearing capacity by assuming that step size is 0.1 and each level of load is 100kN. The change of elastic modulus of the pile is realized by using field variable. Fig.3 shows the horizontal displacement nephogram of each pile at the end of pile driving. We can find that the big horizontal displacement of the pile occurs in the corresponding to the silt clay, and the maximum is 6.042mm. All of the piles are bent in an arc and it is negative to the bearing capacity. The pile will be
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Vertical Displacement（mm）
more arched when it is more close to the pile‐driver. Fig.4 shows the curve of the vertical bearing capacity and the vertical displacement. The L in the figure represents that counting from the left side of the pile shown in Fig.3. Fig.4 shows that the three piles on the left side changed obviously, and the bearing capacity of the seven piles on the right side is almost the same with the bearing capacity of the third pile on the left side. It suggests that the safe distance from the pile to the pile‐driver is more than 4.2m. The ultimate bearing capacity of the first to third pile on the left side is 541.18kN, 671.24kN and 789.88kN respectively. The ultimate bearing capacity of the seven piles on the right side is about 800.56kN (the experiment date is 776kN), which means that the bearing capacity of the first pile on the left side have declined 32.4%. 0 -5 -10
L1 L2 L3
-15 -20 0 10
1
2
10 10 Bearing Capacity lgQ（ kN）
3
10
FIG.4 LGQ‐S CURVE(L1:THE FIRST PILE ON THE LEFT SIDE,L2:THE SECOND PILE ON THE LEFT SIDE, L3:THE THIRD PILE ON THE LEFT SIDE)
From the coordinate in Fig.1, fitting the formula of the relationship between the max bearing capacity and the distance of the pile by using the distance to the pile‐driver as the horizontal coordinates and using the max bearing capacity of the pile as the vertical coordinates. We can get
F 0.02025d 3 11.94d 2 142.3d 384.9 (3) Conclusion The pile is bent to an arc because of the self‐weight of the pile‐driver, which is different from the cantilever beam mode that using the pile as the free end to move in the study of the conventional inclined pile. In this paper, we can analyze by combining finite element with experiment data that: (1) The more closer of the distance between pile and pile‐driver, the more deformation of the pile, the smaller of pile bearing capacity. (2) The safe distance between the pile and the pile‐driver is more than 4.2m. (3) The maximally reducing ratio of bearing capacity of the pile is 32.4 percent. What’s more, the formula of the relationship between the maximally bearing capacity of the pile and the distance between the pile and pile‐driver is given in this paper. ACKNOWLEDGMENT
This study was supported by Anhui Province Science &Technology Plan of Construction Industry (No. 2015YF‐26) and Hunan Province Major Hydraulic Science &Technology Plan (No. 【2015】186‐24). REFERENCES [1]
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Journal of Underground Space and Engineering,2015,11 (5) :1152‐1158 Zhou Ziyan was born in Hefei in 1996. She is an undergraduate in Wentian College of Hohai University now, and her major field of study is Port and Waterway Engineering. Zhou Qi was born in Huainan in 1996. He is an undergraduate in Zhaoqing University now, and his major field of study is Financial Mathematics. Yuan Yulu was born in Huainan in 1995. He is an undergraduate in Hohai University now, and his major field of study is Civil Engineering. Li Qian was born in Jiangsu province in 1992. She got her bachelor’s degree at Hohai University in 2015, and she is a graduate student in Hohai University. Her major field of study is Disaster Prevention and Reduction Engineering and Protective Engineering. Zhou Xingde was born in Hefei in 1964. His educational background is listed as follow. He got a bachelor’s degree in Department of Port Machinery in 1987, a Master’s degree in Department of Mechanical Engineering in 1993, a Doctor’s degree in Department of Engineering Mechanics in 2001 and a Post‐doctoral degree in Department of Engineering Mechanics in 2004. His major field of study is Disaster Prevention and Reduction Engineering and Protective Engineering and Modal Parameter Identification. He is working as a professor at Hohai University now. What’s more, he is a director at Jiangsu Institute of Vibration Engineering and an appraisal expert at National Natural Science Foundation of China, Jiangsu province graduate student degree thesis and the Ministry of education too. He has published 《 An improved chaos optimization algorithm based on group searching》 on Proceedings 2010 IEEE Fifth International Conference on Bio‐Inspired Computing: Theories and Applications in 2010, and《A New Active Vibration Control Approach Combined Energy with Feed forward Gain》Third Asia‐Pacific International Conference on Computional Methods in Engineering in 2009.
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