Research On Mechanical Characteristics And Strengthen Method Of Silt In Yellow River Delta

Silt in Yellow River Delta is formed by repeated siltation of old and new accumulation body. Therefore, it varies from silt in other areas. Silt in Yellow River Delta has some special characteristics, such as homogeneous particle size, high degree of roundness, poor interlocking with each other, and high porosity; meanwhile, there are so little clay particles in the silt due to long-term erosion. All of these properties lead to the greatly low strength. More important, the geographical position of Yellow River Delta is near Bohai bay, so the content of soluble salt in this silt is very high due to the reverse permeability of seawater. Because of these special causes of formation and characteristics, this silt has some unsatisfactory engineering properties, such as hard to compaction and controlling of water content, loose of surface after consolidation and low degree of strength. Also, the silt particle will militate against efficient affecting with stabilizer like clay particle. In the meantime, the silt granule can not play a skeleton role in the soil. As a result of these special properties, many of roadbed diseases happen in this area. Therefore, it is necessary to carry out research on mechanical properties for silt in Yellow River Delta, and then put forward a countermeasure.Taking the silt in Yellow River Delta as a research object, laboratory physical tests, chemical tests and micro-analysis were conducted. A lot of in-suit tests and mechanical tests of undisturbed samples were also finished. The mechanical and engineering properties were comprehensively analyzed. Based on this, cheap and environmental protection additives were selected and used to enhance the strength of this special silt soil. The optimal matching program of solidified agent was founded after lots of tests. Finally, mechanical responses and deform characteristics of modified silt were studied. The main research contents and conclusions are as follows:(1) Laboratory physical tests and chemical tests of silt in Yellow River Delta were accomplished. Comparing with ordinary silt, micro-analysis was conducted. The essential reason for the special engineering properties of this silt was clarified.(2) Based on ground investigation and cone penetration test(CPT), pressure meter test(PMT) and dilatometer test(DMT) were carried out. The engineering properties were comprehensively analyzed. The relationship between pro-plastic and ultimate pressure with the depth was obtained. The variation features of bearing capacity of foundation changing with depth were also discovered. Then the variety law between pressuremeter modulus Em and depth was conduced. As for DMT, the changes of dilatometer index ID, static lateral pressure coefficient K0 and horizontal stress index KD with depth are studied; meanwhile, the variations of ED and Es with depth of soil stratum are analysed.(3) Laboratory mechanical tests were carried out for different drilling holes and depth of undisturbed samples. The stress-strain relationship and strength indexes were obtained for this area. Fitted equation of critical failure points for varies depth samples were derived; then internal frictional angle of steady-state for different drilling holes was calculated. Finally, the relationships between peak strength and residual strength were derived for different drilling holes in this region.(4) Improved tests for silt with high content of soluble salt in Yellow River Delta were carried out. Based on the physical and mechanical tests, cheap and environmental protection additives were selected. Then, single-doped tests, double mixed tests, and orthogonal tests were finished. Due to these tests results, the mathematical model of linear programming was founded through optimization analysis. Finally, the optimal matching program of solidified agent was founded, with which the 7d strength can come to 842.64kPa. This value is 12.98 times to the strength of this silt before treated.(5) A typical foundation model of highway was selected. Mechanical responses and deform characteristics of improved silt foundation were studied. The deformation properties of foundation for different actuation duration, running speed, and dynamic load amplitude of cyclic loading were analyzed under static and dynamic, single dynamic load and cyclic dynamic load. The relationships between these factors with surface subsidence were deduced.