Architectural Engineering February 2014, Volume 2, Issue 1, PP.10-14
Finite Elements Analysis on Settlement of Dikethrough Culvert Hongyun Si 1#, Min Chen 2, Qingyang Kong 2 1. Civil Science and Engineering College of Yangzhou University, Yangzhou 225009, China 2. College of Hydraulic Science and Engineering, Yangzhou University, Yangzhou 225009, China #Email:
cqlshy@163.com
Abstract In allusion to the engineering case of outlet culvert on Suoxi river in Maanshan of Anhui Province, the finite element model of dike-through culvert has been built, the settlement of culvert trunk on different treated foundation is considered at runtime, the results of settlement of culvert under the different damaged condition of mixing piles are compared and summarized, and the security status of dike-through culvert is analyzed with actual observed data. Some examples are studied in the paper. The study demonstrates that the result of 3D finite element analysis can reflect the settlement situation of structure more directly and accurately, and can provide more evidences for maintenance of dike-through culvert. Keywords: Dike-Through Culvert; Cement Mixing Pile; Differential Settlement; Finite Elements Analysis
1 INTRODUCTION In order to meet the requirement of flood discharge and irrigation, the release structure such as dike-through culvert is often built behind the levee. If the status of foundation is not qualified, such as mucky soil and silty soil, the foundation need to be strengthened at first, then the construction of dike-through culvert project can be carried out. In recent years, the cement mixing pile has been widely used in soft foundation treatment of variety projects due to its rapid construction speed, damage-free, low cost and better reinforcement. However, because the construction technology and examination methods of deep cement mixing pile are yet to be standardized, it is hard to control its construction quality[1]. In practical engineering, the treatment effect of soft foundation has a direct effect on the settlement and operation of upper-engineering. But traditional calculation methods cannot be combined with the different treatment conditions of actual foundation to calculate the differential settlement. Hence, it is necessary to build the calculation models of different ground treatment by using 3D finite element software to analyse settlement of engineering.
2 THEORY AND METHOD OF CALCULATION In order to analyse the stress state of integral structure of culvert, the holistic model is built by using 3D finite element software to analyse and calculate its settlement. Finite element method is one of the most effective numerical methods to deal with complicated space structural mechanics [2]. For the convenience of finite element analysis, the model of hexahedral elements is used. Various structures are discreted into eight-node parallelepiped isoperimetric element and the units are connected by a finite number of points. Eight-node hexahedral elements are space cable clan units, which is isoperimetric transformed by the cube elements in the standard coordinate system. The freedom degrees of eight-node cubic elements are 24 and the displacement function of elements is shown in the Formula (1).
u 8 ui v Ni vi w i 1 w i - 10 http://www.ivypub.org/AE
(1)
The expression of shape functions Ni is shown in the Formula (2). 1 Ni , , 1 i 1 i 1 i i 1, 2, 8 Where 1 1, 1 1, 1 1 .
,8
(2)
Finite element method is suitable for various complicated deformations and stress, and using different types of elements to disperse in order to improve the computational efficiency and accuracy of engineering problem. Thus it becomes the effective means of engineering analysis. Because the culvert trunk is reinforced concrete structure, and its stiffness is bigger than subsoil’s, the model of reinforced concrete structure is treated as linear elastic constitutive model, which is generalized Hook’s law. The elastic-plastic model, provided by Marc, is adopted for the constitutive model of soil. The total deformation of soil is divided into elastic deformation and plastic deformation, and the former is calculated by using Hook’s law, the latter is solved by using theory of plasticity. The hardening law is assumed to be isotropic, the flow rule is associated flow rule, and the yield criterion is linear Mohr-Coulomb law. According to the loading feature of culvert, foundation, culvert and upper filled soil (including upper levee) is treated as a whole to consider the interaction between them. For the contact between different materials, the contact surfaces are defined by using cohesive model which is in Marc finite element software. The foundation, culvert floor and culvert wall are glued into a whole by glue function which is not slipping relative to each other and great separating force. There is no relative sliding velocity between structures, and the deformation of contact surface meets the continuity condition [3]. The various structures are dispersed into eight-node hexahedral elements, and the elements are connected by a finite number of nodes [4]. The loads are calculated by related specifications [5]. The treated foundation soil is considered as composite foundation, and the elasticity modulus of foundation soil is composite elasticity modulus [6]. In general, the damage status is divided into two categories: symmetry breaking and asymmetry breaking, the first of which has small effect on asymmetry settlement of structures, so the effect of settlement of whole upper structures on foundation, caused by asymmetry breaking, is considered in this paper.
3 CASE STUDY The engineering case for finite element analysis is exiting culvert on Suoxi river of Maanshan in Anhui province.
3.1 Project Overview The Suoxi river outlet engineering, located in Songshi town in Maanshan, contains two parts, one of which is Suoxi river outlet sealing levee and the other is Suoxi river outlet draining culvert-sluice. The reinforced concrete culvert is box structure, elevation of floor is 5.0 m, width of culvert is 2.8 m, thickness of top slab and side wall is 0.4 m, length of culvert is 48.0 m, and there are six pieces of culvert, and length of every piece is 8 m. There are copper water stops in adjacent joints and rubber water stops on internal surface. The commissures are bounded by reinforced concrete. The parameters of foundation soil are shown in table 1. TABLE 1 THE PARAMETERS OF FOUNDATION SOIL
Position Culvert
Foundation Soil
150# Concrete
Elasticity Modulus (MPa) 2.20×104
Poisson’s Ratio 0.167
Volume-Weight (kN/m3) 25.0
Miscellaneous Fill
4.50
0.32
18.4
Weight Loam
4.08
0.31
Mucky Weight Loam
3.40
0.30
Weight Loam
3.60
0.30
Material
Remake
The Self-weight of Foundation is not Considered
3.2 Calculation Model and Design Conditions Take the whole culvert, upper levee and a range of foundation (5.6 m from both ends of bottom board along horizontal direction, the depth of whole foundation is 8.5 m along vertical direction) as calculation model, and divide - 11 http://www.ivypub.org/AE
mesh. The framed bent and hoists on culvert are used as upper loads of culvert. The foundation model adopts fullyconstrained due to the choice of its size range. The coordinate system is as follows: the origin is placed in center of top surface of upriver bottom board; the X axis perpendicular to flow direction directs to lower reaches; the Y axis is pure vertical; the Z axis is parallel to the flow direction. The culvert is divided into 48063 eight-node hexahedral elements. The 3D finite element model about Suoxi outlet culvert is shown in Fig.1.
FIG. 1 THE FINITE ELEMENT MODEL OF SUOXI OUTLET CULVERT
The condition of normal working is taken to calculate culvert structure under the loading function of various operating conditions for the settlement of each point, then from which the change rule of culvert settlement can be analyzed. There are four rows of cement mixing piles under the ground. It is assumed that the underground piles are damaged by row and row form left to right. There are five damage status of underground piles to be analyzed from undamaged to complete damaged.
3.3 Analysis of Calculation Result According to the above calculation model and parameters, the five conditions of piles of Suoxi river outlet culvert structure should be calculated by finite element method. The settlements of Suoxi river outlet culvert on five different foundations are shown in Fig.2, Fig.3, Fig.4, Fig.5 and Fig.6.
FIG. 2 THE SETTLEMENT OF CULVERT WHEN PILE FOUNDATION ARE UNDAMAGED
FIG. 3 THE SETTLEMENT OF CULVERT WHEN ONE ROW OF PILES ARE DAMAGED
FIG. 4 THE SETTLEMENT OF CULVERT WHEN TWO ROWS OF PILES ARE DAMAGED
FIG. 5 THE SETTLEMENT OF CULVERT WHEN THREE ROWS OF PILES ARE DAMAGED
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FIG. 6 THE SETTLEMENT OF CULVERT WHEN ALL PILES ARE DAMAGED
The settlement of each segments of culvert on different pile foundations is shown in Fig.7, Fig.8, Fig.9, Fig.10, Fig.11 and Fig.12.
FIG. 7 THE SETTLEMENT OF THE FIRST SEGMENT OF CULVERT
FIG. 8 THE SETTLEMENT OF THE SECOND SEGMENT OF CULVERT
FIG. 9 THE SETTLEMENT OF THE THIRD SEGMENT OF CULVERT
FIG.10 THE SETTLEMENT OF THE FOURTH SEGMENT OF CULVERT
FIG.11 THE SETTLEMENT OF THE FIFTH SEGMENT OF CULVERT
FIG.12 THE SETTLEMENT OF THE SIXTH SEGMENT OF CULVERT
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Figures show that under the same working condition, the more severe damage on pile foundation is, the bigger the settlement of structure is; while before the pile foundation is completely damaged, the more severe the damage on pile foundation from left to right is, the bigger that differential settlement between left and right side of each segment of culvert is. The field detection result indicates that the differential settlement of the first and second segment culvert between left and right is about 4 cm, the third segment culvert’s is 5 cm, the fourth segment culvert’s is 6 cm. Hence, the damaged condition of pile foundation under the culvert is very serious. There are at least three rows of cement mixing piles that cannot meet the requirement of carrying capacity. The damaged condition of piles under fourth segment culvert is the most severe, and about three or more rows of piles are damaged.
4 CONCLUSION (1) The actual complex engineering can be divided into different types of elements according to different features of deformation and stress by using finite element method, and computational efficiency and accuracy of engineering can be improved. (2) The differential settlement of culvert between left and right side is very serious. The calculated result and field detection result show that the carrying capacity of cement mixing pile can not meet the requirement of prospective. (3) Although the construction speed of cement mixing pile is rapid and the cost is low, its construction quality is hard to control. So it is necessary to control its construction process. The construction experience must be gathered to perfect construction technology step by step.
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AUTHORS Hongyun Si (1967- ), female, bachelor of engineering, associate professor, her major field of study is hydraulic structure. Email: cqlshy@163.com
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