Test Investigation on Liquefied Deformation Structure in Saturated Lime‐Mud Composites Triggered by Strong Earthquakes

Abstract

Three identical model boxes were made from transparent plexiglass and angle iron. Using the method of sinking water and according to the sedimentary rhythm of saturated calcium carbonate (lime‐mud) intercalated with cohesive soil, calcites with particle sizes diameters of ≤ 5 μm, 10–15 μm and 23–30 μm as well as cohesive soil were sunk alternatively in water of three boxes to build three test models, each of which has a specific size of calcite. Pore water pressure gauges were buried in lime‐mud layers at different depths in each model, and connected with a computer system to collect pore water pressures. By means of soil tests, physical property parameters and plasticity indices (Ip) were obtained for various grain‐sized saturated lime‐muds. The lime‐muds with Ip ranging from 6.3 to 8.5 (lower than 10) are similar to liquid saturated silt in the physical nature, indicating that saturated silt can be liquefied once induced by a strong earthquake. One model cart was pushed quickly along the length direction of the model so that its rigid wheels collided violently with the stone stair, thus generating an artificial earthquake with seismic wave magnitude greater than VI degree. When unidirectional cyclic seismic load of horizontal compression‐tension‐shear was imposed on the soil layers in the model, enough great pore water pressure has been accumulated within pores of lime‐mud, resulting in liquefaction of lime‐mud layers. Meanwhile, micro‐fractures formed in each soil layer provided channels for liquefaction dewatering, resulting in formation of macroscopic liquefaction deformation, such as liquefied lime‐mud volcanoes, liquefied diapir structures, vein‐like liquefied structures and liquefied curls, etc. Splendid liquefied lime‐mud eruption lasted for two to three hours, which is similar to the sand volcano eruption induced by strong earthquake. However, under the same artificial seismic conditions, development of macroscopic liquefied structures in three experimental models varied in shape, depth and quantity, indicating that excess pore water pressure ratios at initial liquefaction stage and complete liquefaction varied with depth. With size increasing of calcite particle in lime‐mud, liquefied depth and deformation extent increase accordingly. The simulation test verifies for the first time that strong earthquakes may cause violent liquefaction of saturated lime‐mud composed of micron‐size calcite particles, uncovering the puzzled issue whether seafloor lime‐mud can be liquefied under strong earthquake. This study not only provides the latest simulation data for explaining the earthquake‐induced liquefied deformations of saturated lime‐mud and seismic sedimentary events, but also is of great significance for analysis of foundation stability in marine engineering built on the soft calcium carbonate layers in neritic environment.

The Use of Soft-Sediment Deformation Structures As Proxies For Paleoseismic Activity And Shaking: A Review

“…Therefore, the lique ed diapir in the Luobozhai lacustrine section are attributed to seismic activity, and were not in uenced by ash oods, uvial processes or other processes. Considering that the lique ed diapir in Luobozhai section are strongly deformed, and that the deformed layer contains a notable clay content that will result in a relatively high viscosity, a relatively large magnitude would be required to cause its liquefaction related deformation (Tian et al, 2016;Su and Qiao, 2018). By using the six methods described above to determine the earthquake magnitudes, we suggest that the lique ed diapir in the Luobozhai section may represent earthquake activity with magnitudes 6-7 (Table 2).…”

La Capa de conglomerado-brecha de la Llosa del Cavall (Solsona, Lleida): características sedimentarias

“…La facies gm F2 presenta características mixtas de distintos tipos de flujos densos (debris-flow s.l). Por un lado, la granoclasificación vertical con incremento de matriz hacia techo y la granoclasificación lateral, se relacionarían con flujos capaces de generar una segregación por fracción granulométrica (Lowe, 1982;Talling, 2013) y que conjuntamente con su geometría y extensión se podrían explicar a partir de flujos densos no cohesivos. Por otro lado, la desorganización interna y el empaquetamiento laxo se pueden relacionar con un cierto grado de cohesión, una rápida deposición o debido al escape de agua poral.…”

Soft Sediment Deformation Structures Triggered by the Earthquakes: Response to the High Frequent Tectonic Events during the Main Tectonic Movements

“…Three axis vibration test of saturated soft soil presents when the seismic intensity is 7 or greater (amount to the earthquake magnitude is 5.6), and muds usually do not be liquefied but it happens with thixotropic flow, which is triggered by shocking [55,56]. The earthquake magnitude for thixotropic deformation is higher than liquefied deformation [57]. Many deformation structures in argillaceous rocks, silica rocks and micritic of carbonate rocks can be interpreted by the thixotropic mechanism ( Figure 10C).…”