Compaction and bearing characteristics of untreated and treated lateritic soils with varying moisture content

Compaction and bearing characteristics are important factors in evaluating the quality of subgrade construction, and the compaction moisture content has a significant effect on both characteristics. In this paper, the lateritic soils were taken from three locations: the Guangxi Zhuang Autonomous Region, Hunan Province, and Fujian Province. The lateritic soils from the Guangxi Zhuang Autonomous Region were treated with 0%, 1%, 3%, 5%, and 7% cement. The effects of variable moisture content (ω) on the dry density (γd), California bearing ratio (CBR) values, and resilient modulus (MR) of untreated and treated lateritic soils were investigated by compaction tests, soaked/unsoaked CBR tests, and soaked/unsoaked MR tests. The variation in the microstructure of lateritic soils was analysed by scanning electron microscopy, X-ray fluorescence, X-ray diffraction, and mercury intrusion porosimetry tests. The results show that the optimum moisture content (ωopt) of lateritic soil decreases significantly with increasing cement content, while the maximum dry density (γd,max) increases. Moreover, ωopt and γd,max are exponential functions of the plasticity index (IP). The CBR of lateritic soil showed an obvious decrease after soaking, and the CBR values of the soaked samples were approximately 1.5 times lower than the unsoaked samples under the same conditions. Some of the soaked samples had CBR values lower than the specification values, and the CBR values of lateritic soils increased by 10 times using cement treatment. The moisture content corresponding to the maximum CBR value (ωCBR,max) is higher than ωopt. The empirical relationship of the difference between ωCBR,max and ωopt with IP was established, and the proposed ωCBR,max is used as the compacted moisture content of the subgrade filler. The MR of the soaked samples decreased faster than that of the unsoaked samples, and with the increase in moisture content, the MR of the soaked and unsoaked conditions decreased by 57% and 34%, respectively. With increasing moisture content, the CBR index and MR index, which are the ratios of the test results under unsoaked and unsoaked conditions, decreased by 0.45. With increasing cement content, the moisture sensitivity of the treated soil decreased, while the bearing characteristics are slightly influenced by the varying moisture content. The main reason for the increase in γd, CBR value, and MR of the treated lateritic soils was the increase in the content of elemental calcium and calcium-based compounds. Based on the analysis of the test results, the prediction models between CBR and MR with ω, γd, and IP were established by multiple regression analysis. The prediction model between MR and CBR was established with a correlation coefficient of 0.99. Finally, the procedure of material selection, construction control, and treatment of expressway upper roadbed filler was proposed. The practical application in a test section of an expressway verified that the suggested procedures applied to subgrade construction.