Experimental Study on Mechanism of Wave-Induced Liquefaction of Sand-Clay Seabed

Jun Zhang,Dongsheng Jeng,Xindi Chen,Lizhu Wang,Qin Jiang,Changkuan Zhang

doi:10.3390/jmse8020066

Abstract

In this study, a series of laboratory experiments for the response of wave induced clay-sand seabed were carried out to clarify the mechanism of liquefaction of clayey seabed. The experiments were conducted in an 80 m long wave flume. In the tests, the sand-clay beds were mixed with various clay contents (CC) from 0.5% to 15% and were tested for given wave conditions. The pore water pressure and the water elevation were measured in each test. Soil properties tests and scanning electron microscope (SEM) experiments on different seabed samples were carried out to further explore the mechanism of liquefaction. The experimental results indicated that the amplitude and accumulation of the excess pore water pressure (EPP) varied with different CC in the sand-clay bed. With the introduction of CC, micro-structure and properties (such as permeability and compressibility) of bed soils changed. Sand-clay bed presented more susceptibility to liquefy compared with pure sand bed. CC promoted seabed liquefaction, even if the added amount was very small (CC is 0.5%), however when CC exceeded a certain value (10% in this study), the mixed bed will not be liquefied. This phenomenon can be well explained by the micro-structure of sand-clay bed. CC within a sandy seabed, does not only affect the permeability, but also change the compressibility of seabed soils. For example, the microfabric of seabed vulnerable to liquefaction is loose. Clay aggregations generally gathered at the sand particle contact points. This microfabric is easily compressed under wave loads and allowed pore water to flow, resulting in the accumulation of pore water pressure. On the other hand, the microfabric of seabed that was resistant to liquefaction appeared to be more compact. Due to clay-filled gaps between the sand particles, the pore water is more difficult to flow when seabed was compressed. Furthermore, the tendency of seabed liquefaction is closely related to CC.

Highlights

Wave-induced liquefaction of seabed is an important phenomenon in coastal engineering, because it will cause reduction of effective stress between the soil grains, and uneven settlement of foundation caused by the reduction will result in the damage of structures
It was found that susceptibility of seabed liquefaction was increased with the addition of clay contents (CC) and there is a critical value of CC which liquefaction would not occur when the CC exceeded the critical value
NW is the number of waves required for excess pore water pressure (EPP) reaching PACC. σ0 is the critical mean normal effective stress that used to discriminate seabed liquefaction

Summary

Introduction

Wave-induced liquefaction of seabed is an important phenomenon in coastal engineering, because it will cause reduction of effective stress between the soil grains, and uneven settlement of foundation caused by the reduction will result in the damage of structures. As reported in the literature, there are two main mechanisms of seabed liquefaction under waves: residual vs momentary liquefaction. For most of the coastal zones, seabed soils are generally classified into three categories, i.e., sand, silt and clay. In the past 30–40 years, the phenomenon of wave induced liquefaction has been extensively investigated and numerous factors affecting this process were studied on non-cohesive sand and silt seabed [2,3,4,5,6]. Only limited research has been carried out on wave induced clayey soils because of the widely accepted supposition that clayey soils are in general non liquefiable [7]

Methods

Results

Conclusion