Microstructural changes and micro-macro-relationships of an intact, compacted and remolded loess for land-creation project from the Loess Plateau

摘要

The Loess Plateau accounts more than 6% of China's land area and 45% of Shaanxi Province. The land-creation project could double the city's current area. However, the behavior of loess, and in particular inadequate compacted loess, can have significant implications on the safe and reliable operation of man-made infrastructure. The mechanical behavior and collapsibility of intact, in situ compacted and remolded loess in lab, which are widely recognized as fundamentally different materials, were associated with the microstructure. There is limited understanding of micro-macro-relationships in the three fine-grained loess. This study focuses on the microstructural changes and micro-macro-relationships of an intact, compacted and remolded loess from complex land-creation project. A comprehensive microstructural comparisons about PSDs, micrographs and quantitative evaluation for intact and remolded loess from an 80-m-high section of the sedimentary strata, and compacted loess from a highly filled exploratory well are presented and discussed in this paper. The results show that both the intact and compacted loess exhibit trimodal characteristics in their PSDs, while there are bimodal/unimodal characteristics of the PSD for the remolded loess. The compressibility and the specific surface area of the remolded loess are far less than those of the intact or compacted loess. This is further evidence the remolded loess is not suitable to study the collapsibility and compressibility instead of intact loess. However, compared with the intact loess, the compacted loess shows the same pore and particle flocculation structure characteristics for samples at higher density ( 1710 kg/m(3) + 10 kg/m(3)). Under high-energy impact load, particles perform the breakdown, from round, coarse and disordered particles gradually to flaky, fine and ordered particles, which are different from traditional research results. The threshold value of dry density 1710 kg/m(3) + 10 kg/m(3) can be defined the boundary and micro-macro-relationships among intact, compacted and remolded loess. The results are of great importance to understand the microstructure characteristics and improve the engineering construction safety in loess areas.