河西砂类盐渍(硫酸盐)土地基中胶结层形成原因初探

在西部干旱、半干旱粗颗粒盐渍土地区的工程建设中,发现近地表地基中存在盐分胶结层(俗称盐圈),这对工程建设意义重大。但截至目前,对其形成原因的研究甚少,对该问题的认识尚不深入。为研究胶结层形成过程,笔者在工程项目较多的河西走廊敦煌选择了场地做现场试验观测。该场地为砾砂地层,其间夹有若干细沙薄层,在现场开挖探井(至年变化深度7.5m以下),观测了该地层在一个冬季171d中的盐分、水分和地温变化情况。试验观测到盐分表聚的过程,还测到冬季由地温梯度形成的水盐迁移,其影响深度超过年变化深度; 只要有一定的地温梯度和合适的水分含量,胶结层的含盐量一直在增加,工程上关心的近地表(5.0m以内)地层的工程性质仍不稳定。

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.