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Analysis of a Deep Excavation in Shanghai Soft Clay

Analysis of a deep excavation in Shanghai soft clay


A deep multistrutted metro station excavation in Shanghai soft clay was reanalyzed with the DeepEX software program. The observed responses of the diaphragm walls and the ground surface were originally presented in a paper by G.B. Liu & J. Jiang from Tongji University, Shanghai, China and C.W.W. Ng from the Hong Kong University of Science and Technology, HKSAR.


EXCAVATION MODEL


In the original publication, the measured diaphragm wall deflections and ground settlements were compared with some case histories in Shanghai and excavations in soft clay in other locations in Asia. The purpose of this analysis is to reanalyze the model with DeepEX software and compare the program estimated results with the presented measured deflections.


xmetro_in_shanghai_study_model

Figure: Cross section 1-1


Surface El: +3.7 m , Water Table El: +2.7 m


SOIL CONDITION


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Figure: Soil profile in publication


Table: Assumed soil properties in deep excavation reanalysis

Assumed soil properties

STRUCTURAL PROPERTIES

Structural properties

Figure: Wall Properties


Support Properties

Figure: Support Properties


MODEL IN DEEPEX


We have simulated this excavation model with our shoring design software program, DeepEX. In DeepEX we can simulate all construction stages in the same project file, so we can monitor and analyze each stage. The following figure presents the final excavation stage.


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Figure: Model Simulated in DeepEX


According to the original publication, there is a 3m compaction grouting below the final excavation to increase the soil strength in this part. We simulated this compaction grouting in DeepEX by assigning a soil change command, that allowed us to apply a stiffness multiplier in all stages on the resisting side (excavation side).


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Figure: Soil Change Commands in DeepEX – Assign Stiffness Multiplier


WALL DEFLECTIONS


The Nonlinear analysis in DeepEX software estimates a maximum wall displacement of 5.03 cm in the final excavation stage. The following figure presents the calculated wall moments and wall deflection diagrams.


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Figure: DeepEX – Final Excavation Depth – Calculated Wall Moments and Wall Deflections


According to the original publication, seventeen inclinometers were used to monitor lateral wall displacements. The maximum measured wall displacement at the final excavation depth (see following figure) was 5.45 cm, verifying the DeepEX calculated wall lateral deflections!


xmetro_in_shanghai_study_deflections.jpg__800x0_q85_subsampling-2_upscale.jpg.pagespeed.ic.Ueon10MLoJ.jpeg

Figure: Maximum Measured Wall Displacements at Final Excavation Depth


 

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DeepEX - Shoring Design Software

DeepEX - Shoring Design Software


DeepEX is the ultimate software program for design and analysis of Deep Excavations! Design any wall type and support system in the most efficient way!

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