IN-SITU TEST STUDY ON CAUSES OF CEMENTED LAYER IN HEXI SANDY SALINE(SULFATE) LAND BASE

Construction projects in arid(semi-arid) coarse saline soil area in the west of China have resulted in the finding of a salt cementation layer(commonly known as salt layer).It has great significance for engineering project. It exists near-surface ground. So far the it has still not been detailed enough. In order to study of the cementation layer formation process, a field test was designed in Dunhuang area within the Hexi corridor. The test site is a gravel sand strata which is interposed with a number of thin sand layer. An exploratory well with 7.5m depth(deeper than annual change depth) was excavated in this site. The data of salt content, moisture content and ground temperature of the section were observed in 171 days in winter. From this test, it observed the process of salt migrated and accumulated to the near-surface ground, as well as measured the migration of water and salt by the geothermal gradient, which impact over the annual changes depth. It is found that as long as there is some geothermal gradient and the appropriate moisture content, the salt content of the cemented layer would continue to increase. Engineering concerned with the engineering properties of the formation in the near-surface(within 5.0m depth) remains uncertain.