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Frontiers of Structural and Civil Engineering

ISSN 2095-2430

ISSN 2095-2449(Online)

CN 10-1023/X

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Front. Struct. Civ. Eng.    2016, Vol. 10 Issue (4) : 488-498    https://doi.org/10.1007/s11709-016-0338-x
RESEARCH ARTICLE
Model test of the group piles foundation of a high-speed railway bridge in mined-out area
Xin LIANG1,2,Qian-gong CHENG(),Jiu-jiang WU1,Jian-ming CHEN1
1. Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 611756, China
2. Faculty of Civil Engineering, Guangxi University of Science and Technology, Liuzhou 545006, China
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Abstract

The research on the mechanism of pile-soil-cap-goaf interaction and settlement of high-speed railway bridge located in mined-out area is still relatively rare. By taking the pile group of Guanshandi bridge foundation in Hefei-Fuzhou high-speed railway as the prototype, a model test is carried out. According to the similarity theory, the similar constant is derived and the similar model material is determined. Meanwhile, three types of data including the bearing behavior of piles, and the settlement law, and soil among piles are investigated. It can be found that: the influence of goaf on the bearing capacity of pile is inversely to the loading degree, the larger of loading degree, the smaller impact of goaf on the bearing capacity. There is no negative side friction can been found in pile body and the degree of downward tendency for the barycenter of side friction layout is obvious for piles in goaf. Although the bearing ratio of soil resistance under cap is relatively large, the cap effect is suggested be ignored considering the characteristic of goaf. There is a maximum critical value for the uneven settlement of pile group in goaf, and when the value is reached, the uneven settlement stop growing anymore. In addition, the formula for calculating bearing capacity and settlement of pile group in goaf based on test results, theory analysis and related standard is established.
Keywords high-speed railway      mined-out areas      goaf      group piles foundation      physical model test      bearing capacity      settlement     
Corresponding Author(s): Qian-gong CHENG   
Online First Date: 09 November 2016    Issue Date: 29 November 2016
 Cite this article:   
Xin LIANG,Qian-gong CHENG,Jiu-jiang WU, et al. Model test of the group piles foundation of a high-speed railway bridge in mined-out area[J]. Front. Struct. Civ. Eng., 2016, 10(4): 488-498.
 URL:  
https://academic.hep.com.cn/fsce/EN/10.1007/s11709-016-0338-x
https://academic.hep.com.cn/fsce/EN/Y2016/V10/I4/488
Fig.1  Foundation layout and stratigraphic distribution (unit: m)
physical quantity similarity relation (p) similarity constant
elasticity and deformation modulus π = E/gl CE = Cg·Cl = 37.5
uniform distributed load π= q/gl Cq = Cg·Cl = 37.5
stress π = s/gl Cs = Cg·Cl = 37.5
strain π = e Ce = 1
Poisson ratio π = u Cu = 1
internal friction angle π = j Cj = 1
cohesion π = c/gl Cc = Cg·Cl = 37.5
linear displacement π = d/l Cd = Cl = 25
Tab.1  Similarity constant of physical quantity
Fig.2  Bridge pile group foundation model and model tank dimension (unit:m)
load/kN PPR cross section area /m2 stress/kPa mean strain /me elasticity modulus /103 MPa
0.4 0.0003886 1029 1058 0.973
0.8 0.0003886 2059 2127 0.968
1.2 0.0003886 3088 3265 0.945
Tab.2  The experimental result of the elastic modulus of PPR pipe
material No. river sand quality/kg gypsum quality/kg cement quality/kg water cement ratio elasticity modulus/MPa compressive strength/MPa
1 1.0 0.16 0.06 0.23 283 0.46
2 1.0 0.12 0.10 0.17 217 0.29
3 1.0 0.12 0.10 0.17 217 0.29
4 1.0 0.05 0.07 0.10 176 0.28
5 1.0 0.09 0.04 0.10 457 0.76
6 1.0 0.10 0.03 0.10 389 0.67
Tab.3  Model material mix proportion and mechanical parameters
load class prototype load/kN prototype stress/KPa model load
/N		 model stress
/kPa		 test load
/N
class 1 (Pier body) 12000 297.64 512.19 7.94 500
class 2 (single beam) 16500 409.26 703.7 10.91 670
class 3 (dual beams) 20000 520.87 896 13.89 890
class 4 (self-weight of structure+ train load) 24523.73 608.27 1046.35 16.22 1110
class 5 (additional) 33049.86 819.75 1410 21.86 1410
class 6 (additional) 43360.93 1075.5 1850 28.68 1850
class 7 (additional) 57421.49 1424.25 2450 37.98 2450
Tab.4  Load classification
Fig.3  Model loading process
Fig.4  Layout of the monitoring points (unit: m)
Fig.5  Axial force of piles. (a) No. 3; (b) No. 5; (c) No. 7
load class 1 2 3 4 5 6 7
No.3 1 1 1 1 1 1 1
No.5 1.26 1.16 1.09 1.07 1.09 1.09 1.09
No.7 0.79 0.86 0.89 0.91 0.93 0.937 0.955
Tab.5  Comparatively value of pile top loads
Fig.6  Side friction of piles. (a)No. 3; (b) No. 5; (c) No. 7
Fig.7  Soil stress change curve between piles
Fig.8  Stress change curve of pile top and pile tip
pile stress of pile top/kPa stress of pile tip/kPa tip resistance percent side friction percent
No. 3 295.0 23.7 8.0% 92.0%
No. 5 320.3 33.1 10.3% 89.7%
No. 7 281.0 16.1 5.7% 94.3%
Tab.6  Stress of pile top and pile tip under the maximum load
Fig.9  Bearing ratio of pile and soil
Fig.10  Settlement curve of cap and soil between piles
Fig.11  Settlement curve at the bottom of the roof of roadway
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