Liquefaction Analysis

Liquefaction analysis to enhance your earthquake preparedness by evaluating the bank protection, revetment, and/or river bank effectivity

Keywords

and/or river bank effectivity,Liquefaction analysis to enhance your earthquake preparedness by evaluating the bank protection,revetment

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Solution Overview

When a soil is hit by a repeated shearing stress like an earthquake, a phenomenon called liquefaction sometimes occurs. When the effective stress is lost due to the repeated shearing stress, the soil loses its stability. When the soil loses the stability, the pore-water pressure increases and the liquefaction occurs.
Typically, the liquefaction judgment is done by a simple method that uses the FL value. In addition to this simple judgment, KKE will conduct the two dimensional and three dimensional evaluations through the total stress analysis and effective stress analysis, using the finite element method. We can provide the liquefaction judgment that includes more detailed FL value and the evaluation of the excess pore-water pressure ratio.

Mechanism of Liquefaction

In the following figure, the black area represents the ground particle, and the gray area represents the water area. As shown in (a), the ground is stable before the earthquake because the ground particles are interlocked with each other. However, as the earthquake occurs the ground receives repeated shearing stress, and the ground particles are separated from each other as shown in (b) and the effective stress is completely lost. At that point the ground turns into liquid state. Also after the earthquake, as the particles continue to go down, the water level will rise as shown in (c).

Mechanism of Liquefaction

Mechanism of Liquefaction

Benefit of Liquefaction Analysis (Effective Stress Analysis)

It's possible to evaluate the liquefaction by the total stress analysis. However, in the total stress analysis, the forces that effect earth and water respectively are combined together and evaluated as a total stress. By performing the effective stress analysis, we can evaluate the forces that effect earth and water separately as the effective stress and pore-water pressure respectively, which is important in the analysis of the liquefaction phenomenon. Also, with the effective stress analysis, more detailed evaluation is possible. This is directly linked to the evaluation of the analysis results. Since in the effective stress analysis the pore-water pressure and effective stress are handled separately, it's possible to calculate the excess pore-water pressure ratio, and by tracing the ratio at the time history level, we can evaluate and simulate the timing of the liquefaction occurrence more rigorously.

Relevant Software

※1:NANSSI is a product co-developed by the Kozo Keikaku Engineering, Inc. and Jishin Kougaku Kenkyusho, Inc.

※2:FLIP is a liquefaction-induced structure damage prediction program developed by the former Port and Harbor Research Institute, Ministry of Transport.

※3:LIQCA is a finite element analysis program based on the effective stress analysis method, co-developed by Kyoto, Gifu, Tohoku, and other universities.

Analysis of the Ground Liquefaction and Lateral Flow

Below is an case study of the ground near sea shore. We studied whether or not the liquefaction would occur, and evaluated the effect that the ground of the surrounding areas would receive when the liquefaction has actually occurred. The analysis result shows that the excess pore-water pressure ratio is almost 1.0 (the effective stress is about zero). It indicates that the liquefaction is continuing and ground displacement is increasing.

Excess Pore-Water Pressure Ratio Contour Figure Excess Pore-Water Pressure Ratio Time History
Excess Pore-Water Pressure Ratio Time History
Displacement Time History
Excess Pore-Water Pressure Ratio Contour Figure Displacement Time History

For More Information

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E-Mail: kaiseki@kke.co.jp

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