Liquefied sandy soil

Sand liquefaction refers to loose saturated sand below the groundwater level, which often becomes more dense after being shaken. However, the pores of saturated sand are all filled with water, so this close action will lead to a sudden increase in pore water pressure, which will not dissipate in a short time during an earthquake, thus reducing the pressure (effective pressure) originally transmitted by sand particles through their contact points. When the effective pressure disappears completely, the sand layer will completely lose its shear strength and bearing capacity and become liquid-like, commonly known as sand liquefaction.

The saturated sandy soil and saturated silt in this area have the macroscopic conditions of liquefaction. There are phenomena such as water spraying, sand blasting and ground fissure during historical earthquakes. Its liquefaction degree is affected by the following factors: particle characteristics, density, permeability, structure, compaction state, overlying soil layer, buried depth of groundwater level, drainage conditions, stress history, earthquake intensity and duration, etc.

Liquefaction discrimination is to judge the possibility of soil liquefaction in earthquake according to the physical and mechanical properties of soil and other engineering geological conditions. The national standard "Code for Seismic Design of Building Foundations" (GBJ 1 1-89) stipulates the liquefaction discrimination method of saturated sand and saturated silt. When judging the liquefaction of saturated sand and saturated silt in this area, the liquefaction critical value and liquefaction index are calculated according to the macroscopic judgment of liquefaction potential and the in-situ test data-standard penetration test. See table 2- 1 1 for the liquefaction grade of foundation according to liquefaction index. The distribution law of liquefied sand in this area is as follows (Figure 2-8).

Figure 2-8 Liquefaction Zoning Map of Saturated Sand in Yellow River Delta

Figure 2-8 Zoning Map of Saturated Sand Liquefaction in the Yellow River Delta

Table 2- 1 1 foundation liquefaction grade table 2-1/foundation liquefaction grade

1. Severe liquefaction area

1) is distributed in the middle and upper reaches of the Yellow River flood mainstream belt at the apex of the modern Yellow River Delta, showing a north-south fan shape, mainly distributed in Chen Zhuang Town-Liuhe Township, Hutan Township-Yihe Town.

2) Scattered in abandoned river belts and crevasse fans, as follows: the first line of Yong 'an Township-Guang Bei Reservoir in Dongying District is a strip-shaped distribution, which is an abandoned river belt; Dianzi Township-Liuqian Township, Lijin County, is distributed in a sheet shape, which is the middle of the crevasse fan; Near Shikou Township in Dongying District, west of Liuhu Town in Dongying District, and northeast of Xinhu Township in Hekou District.

Saturated silt and saturated silt in this area have uniform particles, low clay content, large deposition thickness, new formation age, poor consolidation degree and are most likely to liquefy.

2. Medium liquefaction zone

1) is distributed in the east of Lijin County, Dongying District-Mingji Township-Dazhao Township, Shengli Township-Dongji Township-You Guo Township, and the larger crevasse fan and the slope area at the front of the crevasse fan.

2) It is distributed in the main flood zone of the Yellow River or its marginal zone, Ninghai Township-Kenli County, Chen Zhuang Town-Fuwo Township, east of Bohai Farm-Jianlin Township-Xin 'an Township, and south of Yihe Reservoir-Hekou District.

3) There are sporadic patches in the coastal low area, No.5 pile and the eastern area; Northeast of Diaokou Wharf-north of Gubei Reservoir; The offshore areas in the west and north of Xinhu Town. This area is generally located at the periphery of severe liquefaction area and the top of crevasse fan or scattered in a small area of the main stream of the Yellow River. Saturated silt and silt have low clay content and poor degree of consolidation, which are easy to liquefy.

3. Mild liquefaction area

1) is distributed on the edge of the floodplain and crevasse fan in the ancient Yellow River Delta, as follows: Southern Song Township in Lijin County-Northern Song Township, Longju Township in Dongying District-Chenguan Township in Guangrao County-Dingzhuang Township.

2) It is distributed in the non-Yellow River flood mainstream zone of the modern Yellow River Delta, such as the following zones: Wangzhuang Township of Lijin County-Shengtuo Township of Kenli County, Jixian Township of Lijin County-East of Kenli County, Taiping Township of Hekou District-Yihe Reservoir.

Silt and silt in this area have small deposition thickness, high clay content and light liquefaction degree.

4. Non-liquefied area

1) is distributed in the piedmont alluvial-diluvial plain south of Xiaoqing River in the working area. The groundwater level in this area is deep, and the saturated silt and silt below the groundwater level are relatively dense and not easy to liquefy.

2) Distributed in the coastal lowlands of the coastal zone. In addition to estuarine facies deposits, the clay content in the strata is high or mainly clay, which is not easy to liquefy.