Model Test on the Influence of Surcharge, Unloading and Excavation of Soft Clay Soils on Shield Tunnels

In view of the influence of symmetrical surcharge, unloading and excavation of soft clay soils on shield tunnels, the surface settlement, tunnel settlement, vertical additional earth pressure and tunnel additional confining pressure are measured by an indoor model test. The changes of confining pressure, tunnel settlement, surface settlement and vertical earth pressure caused by surcharge, unloading and excavation are studied and analyzed. The results show that, in soft clay, surcharge will cause tunnel settlement, and unloading and excavation will generally cause tunnel uplift. There is hysteresis in surface settlement and tunnel settlement above the shield tunnel caused by surcharge and unloading; the change of additional confining pressure of the shield tunnel caused by surcharge is mainly concentrated in the three directions of 3, 5 and 7 of the radar chart. These points belong to weak points. Unloading and excavation can effectively reduce the additional confining pressure of the tunnel in these three directions; excavation will cause the increase of vertical cumulative additional earth pressure and tunnel confining pressure in local directions. The influence range of surcharge in soft clay is wider than that in sand, but the depth is relatively shallow.

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LONG TERM PREDICTION OF VERTICAL EARTH PRESSURE LOADING ON A SHIELD TUNNEL IN SOFT CLAY GROUND

Journal of Japan Society of Civil Engineers Ser F1 (Tunnel Engineering) ◽

10.2208/jscejte.73.i_75 ◽

2017 ◽

Vol 73 (3) ◽

pp. I_75-I_84

Author(s):

Shigeaki OKA ◽

Yoshihiro ITO ◽

Ayaka YOKOTA ◽

Jin SAITO ◽

Shunsuke KANEKO ◽

...

Keyword(s):

Soft Clay ◽

Earth Pressure ◽

Shield Tunnel ◽

Pressure Loading ◽

Term Prediction ◽

Clay Ground ◽

Long Term Prediction ◽

Vertical Earth Pressure

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Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test

Applied Sciences ◽

10.3390/app12010081 ◽

2021 ◽

Vol 12 (1) ◽

pp. 81

Author(s):

Inyeop Chu ◽

Sang-Kyun Woo ◽

Sang Inn Woo ◽

Joonyoung Kim ◽

Kicheol Lee

Keyword(s):

Model Test ◽

Earth Pressure ◽

Centrifuge Model Test ◽

Gravitational Acceleration ◽

Soil Pressure ◽

Geotechnical Centrifuge ◽

Centrifuge Model ◽

Cover Depth ◽

Box Culvert ◽

Vertical Earth Pressure

Due to the lack of surface space, most structures are heading underground. The box culvert is underground infrastructure and serves to protect the buried structure from the underground environments, but it has a different characteristic from other structures in that the inner space is empty. Therefore, in this study, the vertical earth pressure which is the most significant effective stress acting on a box culvert was measured by conducting a geotechnical centrifuge model test. A box culvert was installed following the embankment installation method, and the vertical earth pressure acting on it was measured considering the cover depth, gravitational acceleration, and loading and unloading conditions. The soil pressure measured was greater than the existing theoretical value under high cover depth and the unloading condition, which is considered as the variability of many soils or the residual stress acting under the loading condition. Finally, a goodness-of-fit test was conducted as a part of variability analysis. The measured earth pressure was found to be considerably larger than the existing theoretical value, and the variability was large as well. This means the existing theoretical equation is under-designed, which should be reflected in future designs.

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