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Research Papers: Ocean Engineering

Seepage Induced Soil Failure and its Mitigation During Suction Caisson Installation in Silt

[+] Author and Article Information
Lizhong Wang

e-mail: wlzzju@163.com

Luqing Yu

e-mail: yuluqingcugb@126.com

Zhen Guo

e-mail: nehzoug@163.com
College of Civil Engineering and Architecture
and Research Center of Coastal
and Urban Geotechnical Engineering,
Zhejiang University,
Yuhangtang Road 866,
Hangzhou 310058,
Zhejiang, China

Zhenyu Wang

College of Civil Engineering and Architecture,
Zhejiang University,
Yuhangtang Road 866,
Hangzhou 310058,
Zhejiang, China
e-mail: wzyu@zju.edu.cn

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received April 16, 2013; final manuscript received October 8, 2013; published online November 12, 2013. Assoc. Editor: Dong S. Jeng.

J. Offshore Mech. Arct. Eng 136(1), 011103 (Nov 12, 2013) (11 pages) Paper No: OMAE-13-1036; doi: 10.1115/1.4025677 History: Received April 16, 2013; Revised October 08, 2013

Suction caisson is an advantaged foundation option for offshore wind turbines in sandy and clayey soils. In this work, a series of model tests were conducted to investigate the installation behavior of a suction caisson in silty soils. The test results showed that the total soil resistance to the caisson increased steadily with penetration depth in the beginning of the suction-assisted penetration (SP) process, but rose slowly or remained constant after reaching a certain depth with excessive soil heave. This failure mechanism, which was quite different from that identified in sandy or clayey soils, was caused by the seepage induced silt soil failure in the caisson, such as erosion, liquefaction or piping, with reducing internal side friction and tip resistance. To suppress this type of failure, a special filtration method was introduced to help caisson penetration. The test results showed that such filtration technique had the advantage of reducing the height of soil heave and prevent seepage induced soil failure in the silt, but also suppress the under pressure effects on reducing the soil resistance. Numerical simulations were also performed to aid in understanding the observed test results and mitigation mechanisms.

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Figures

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Fig. 1

(a) Photo of the caisson model and (b) corresponding sketch

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Fig. 2

Illustration of the soil tank and its bottom drainage system (a) soil tank and (b) drainage system

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Fig. 3

(a) Site of the soil acquired and (b) particle distribution curve of the soil used in the test

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Fig. 4

Positions of the soil samples acquired and CPTs in the tank

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Fig. 5

(a) Apparatus of the cone penetration test and (b) cone resistance results

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Fig. 6

Model test equipment system (a) dead-weight loading rig and (b) suction installation apparatus

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Fig. 7

Locations and dates of model caisson installation tests within the soil tank (a) SP-1, SP-2, SP-3, and JP and (b) SPF-1, SPF-2, and SPF-3

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Fig. 8

Penetration depth versus time in tests SP-1, SP-2, SP-3, and JP

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Fig. 9

Variations in suction pressure in tests SP-1, SP-2, and SP-3

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Fig. 10

Predicted and measured rate of seepage flow in tests SP-1, SP-2, and SP-3 (a) SP-1 (b) SP-2 (c) SP-3

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Fig. 11

Measured and predicted installation resistance with penetration depth

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Fig. 12

Hydraulic gradient and soil resistance with penetration depth (a) SP-1 (b) SP-2 (c) SP-3

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Fig. 13

(a) Photo of the filter layer applied in the test and (b) sketch of the filtration technique

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Fig. 14

Penetration depth versus time in tests SPF-1, SPF-2, and SPF-3

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Fig. 15

Variations of suction pressure in tests SPF-1, SPF-2, and SPF-3

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Fig. 16

Soil resistance in tests SPF-1, SPF-2, and SPF-3

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Fig. 17

Equipotential lines for caisson with different filter layer permeabilities (a) without filtration (b) kf/k = 1/5 (c) kf/k = 1/10 (d) kf/k = 1/20

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