Abstract:Loess in China are mainly distributed in the terraces of the Yellow River，including in the Gansu, Ningxia,Inner Mongolia,and Shanxi provinces, covering an area of 6.4×106 km2 that accounts for about 6.6% of China's territory. The loess in western Gansu belongs to the class of unsaturated loess with a wide distribution range. Formed near the sand source, the eolian loess mainly includes sand loess, low-viscosity loess, and clay loess.Low-viscosity loess in Gansu has large thickness, with development pores and aerial weak cementation, which under dynamic loading is likely to produce large settlement deformation. It also has strong water-collapse characteristics and a tendency toward liquefaction. Such material brings arduous engineering challenges and foundation treatment construction problems. Low-viscosity loess in general has weak alkaline and poor cementation strength, with large deformation under a force dynamic. Because underground water easily uplifts after loading, liquefaction is a serious problem. Acid modified and chemically modified technology can effectively improve the loess seismic subsidence problem. The principle of acid-modified loess chemical modification is using phosphoric acid and a weak acid as a loess acidification treatment, considering that the loess formed in a dry climate gives priority to calcium carbonate. Then, other salts (Boric salt) are added to form the cementation bonds such as boron bridge bonding and hydrogen bonding. Filling material (calcium salt) is added to adjust the ratio of particle size to reduce the liquefaction potential. The acid modified method reduces the low-cohesion loess' ability to liquefy. The liquefaction test showed that under 50~65 kPa dynamic stress, the modified loess had a very slow rise in pore water pressure , a very small deformation, and almost no stress reduction. Under a dynamic stress of 65 kPa, its liquefied deformation was no more than 0.2%, corresponding to resistance to an IX-level earthquake. The following ratio was confirmed: 10%~30% calcium, 6%~13% boron material with 3% phosphoric acid. If a higher level of anti-seismic resistance is required, add 8%~13% of boron material. The acid-modified method creates no chemical toxicity, and the price of the raw boron material is lower than that of the lime cement. Therefore, this method has some economic and social benefits.
