Risks of using artificial sand base in difficult geotechnical conditions
Excavation of pits, trenches for foundations of civil buildings and industrial structures in saturated clayey soils often leads to soil structural change and great decrease in the soil strength and deformation characteristics. In some cases, an artificial sand base is used as a method for construction on saturated clayey soils. However, technology violations and unsuitable material used during construction can be the reason for excess settlement of the erected facilities. The analysis of domestic regulatory literature performed by the authors showed that building codes allow the construction of artificial embankments from materials of various fractions - from clayey to crushed stone. The study includes a real example of an emergency situation at gantry crane railways with three hundred meters in length in the town of Tobolsk. The observed excess non-uniform base deformations were up to 240 mm. The artificial base was made using local sand with specific properties such as subsidence and frost heaving, which were not taken into account in the design process. The base properties of the silty sand were analyzed in a laboratory study. The purpose of this study was to determine the dependence of the compaction coefficient of silty sand on the loading trajectory and the process of water saturation, as well as to identify the proportion of the subsidence deformation from the final deformation. It has been established that the subsidence of an artificial base made of silty sand is about 12% of the actual deformation of the base. In this case, the deformation of the artificial base from the full operational load, taking into account the process of water saturation, is approximately 30%. The dependence of the final compaction coefficient on the initial one is obtained, which can be used to determine the required compaction coefficient of silty sands when they are used at construction sites. An alternative technique for arranging artificial sand bases to obtain the maximum soil compaction coefficient, which is widely used within the region, is presented.