Loess is a kind of soil that experiences a long period of deposition, and it is relatively stable under natural conditions. However, in the process of engineering construction in loess areas, the original soil structures of the loess are destroyed, inducing changes in the composition and water content in the loess. These changes may cause different environmental and engineering geologic problems. To reveal the engineering properties of disturbed losses in the Chinese Loess Plateau, the physical properties of 135 groups of disturbed loess samples in Yan’an City were analyzed statistically, and the compression properties of loess with different moisture contents and dry densities were studied by high-pressure consolidation experiments. We elucidate the compressive deformation law for perturbed solids at different moisture contents and dry densities. The experimental results show that the water content rate for the best compaction performance of the disturbed loess is 16%. The compressive deformation coefficient generally decreases with increasing dry density and water content. However, when the soil moisture is low, a small amount of water and salt is concentrated in the contact position of the powder, and the soluble salt is condensed into cement. The molecular forces between particles and the bonding forces of bound water and capillary water are larger. The soil forms a porous structure with coarse grains as the main skeleton, and the cement bonding strength is strong at the contact points of the coarse grains. As a result, the loess shows high intensity at low-water content. This results in a compression-deformation coefficient that increases with dryness density in the small load range.

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Influence of Moisture Content and Dry Density on the Compressibility of Disturbed Loess: A Case Study in Yan’an City, China

A manifestation of the effects of structural mechanics is the relationship linking the structure of soil and mechanical behavior. Compaction is a mechanical process modification of soil structure by the expulsion of pore air from the voids, whereas consolidation is a process of expulsion of pore water pressure in which settlement takes place. Secondary compression generally happens after the end of primary consolidation may demonstrate a steady decrease or increase over a substantial period. In order to calculate long-term foundation deformation, understanding the impact of secondary compression is fundamental. Foundation failures can happen by either shear failure or settlement failure, whereas shear failure is instantaneous and settlement failure occurs over a while. Depending on the magnitude and demographic location of the structure, the permissible settlement of the structure should not settle more than 25 and 40 mm allowable as per IS guideline to minimize distress to the foundation. The present experimental study is made on five field soils, and two soils having a liquid limit of 55% and another three soils of 68% of a liquid limit have been also considered. These soils were subjected to IS light and heavy compaction energy levels and static compaction to attend the desired compaction characteristics and achieve the required OMC and MDD; additionally, soils were subjected to a one-dimensional consolidation test from a seating load of 6.25–1600 kPa through a load increment ratio of 1 for different placement conditions. The variation of void ratio with pressure for the soil having a different clay mineralogy for different placement conditions was analyzed. Correlations were developed between pressure and the magnitude of secondary compression, for soils having different clay mineralogy.

A Study on Secondary Compression of Compacted Fine-Grained Soils

Coefficient of secondary compression is one of the important consolidation properties of fine-grained soils exhibiting high secondary compression. Generally, soils containing significant amount of organic matter exhibit high secondary compression. It is generally determined by performing laboratory one-dimensional incremental loading (IL) consolidation test, in which each increment is allowed for 24 h or more. Typically, conventional one-dimensional IL consolidation test takes about 10–14 days to complete. Therefore, end-of-primary consolidation (EOP) test and rapid one-dimensional consolidation tests were developed in the literature to reduce the duration of conventional IL tests. The limitation of these methods is that coefficient of secondary compression cannot be determined as the specimen is not allowed to reach the secondary compression phase. This paper describes a method of determining coefficient of secondary compression from accelerated incremental load consolidation testing procedure using \(\sqrt{t}\) method. In the proposed method, one of the pressure increments is left for sufficiently long time to obtain the linear secondary compression phase in the log t plots. The suggested procedure is validated by comparing the results obtained from the conventional IL consolidation test on four soil samples with varying range of secondary compressibility and plasticity characteristics.

R. G. Robinson

Papers

Determination of Coefficient of Secondary Compression in Accelerated Incremental Loading Consolidation Test