Abstract
With the development of human society, mega engineering projects of removing the tops of hills to infill valleys began to appear in the loess region. The thickness of the manual filling compacted loess can reach tens of meters. For such large-scale construction projects, studying the properties of compacted loess is essential to ensure the safety and reliability of land creation and artificial infrastructure. In this paper, the specimens from two exploration well profiles were carried out to study the physical properties of natural loess and compacted loess from the Loess Plateau. Here the natural loess selected was deposited in old ages (Q2 and Q1) and had strong stability. The natural water content, dry density, specific gravity, liquid limit, plastic limit, plasticity index, clay fraction, silt fraction, sand fraction, compression modulus, and permeability coefficient have been determined. Statistical theories such as t test and correlation coefficient checks were used to describe the difference between the two kinds of loess, and the degree of correlation among various indicators. Besides, 14 groups of exploration well data in 8 studies were collected. The variation of natural water content and dry density with well depth was analyzed to supplement the existing data. Results have shown that the manual filling compacted loess is significantly different from the natural loess. On the whole, the liquid limit, plastic limit, plasticity index, clay fraction, silt fraction, sand fraction and compression modulus of the compacted loess are smaller. In addition, compared with the natural sedimentary loess with strong stability, it deforms more easily. The difference of compression modulus between the compacted loess and natural loess is mainly controlled by the dry density and the particle composition. Moreover, the heterogeneous level of the manual filling compacted loess is greater than that of the natural loess in the horizontal direction and smaller than that of the natural loess in the vertical direction. Under a combination of external hydrologic conditions and dead weight, the compacted loess will become more stable.
Highlights
Loess is a predominantly silt-sized Quaternary sediment which has a wide distribution in arid and semi-arid regions (Peng et al, 2018)
The natural water content of the compacted loess specimens is concentrated between 10.0% and 16.0%, while that of the natural loess specimens is between 5.0% and 20.0%
With the exception of the three groups of data from monitoring equipment, the natural water content of the compacted loess is concentrated between 9.0% and 18.0% (Fig. 8a), while that of the natural loess is between 5.0% and 25.0 % (Fig. 8b)
Summary
Loess is a predominantly silt-sized Quaternary sediment which has a wide distribution in arid and semi-arid regions (Peng et al, 2018). Since World War II, it has been used in almost all countries for engineering construction on loess soils (Evstatiev, 1995; Fonte et al, 2018; Gao et al, 2004; Houston et al, 2001). The scale of these projects was generally not large, only involving a small amount of building foundations in most cases, and the thickness of compacted loess was generally no more than 10 meters. It was unlikely to cause widespread changes to the surrounding terrain
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