Experimental Study On Improved Loessusing Cement For Subgrade Of Zhengzhou-Xi'an Dedicated Passenger Special Line

The operation of high-speed railway in high speed, safty and station has presented higher requirements and the engineering characteisics will influence directly the final quality of the subgrade. In our country, considering that the line is long, geological condition is complex and the optimum filling materials are limited, it is difficult to use the optimum filling materials for the entire line not only for the cost, but also for the guarantee of the optimum fillings materials.So expanding the dimension of the available filling materials by using the C cluster fillings and the improved soil as the high-speed railway bedding filling materials have an important meaning for the railway construction in our country.According to the study on the key technology of loess subgrade of Zhengzhou-Xi'an Passenger Dedicated Special Line as well as the technology of the improved loess subgrade and the site detecton, a series of tests have been carried out, such as compaction test, standard indoor consolidation test, shearing test, unfined compressive strength test, CBR test, slaking test, time effect test, wetting-drying test, freezing and thawing cycle test and so on. The paper studied the characteristics of improved loess in different ratio of cement, such as compaction, water stability, strength and durability, analysised some factors influencing to the strength of improved subgrade, such as mixture ratio, density, curing period, the water content and so on. Finally, it determined the optimum cement maxture ratio witch can provide a certain reference evidence for the feasibility of the cement improved loss as the subgrade fillings of Passenger Dedicated Special Line.Meanwhile, Combined with the indoor test on cement improved loess as the filling material for the subgrade construction of Zhengzhou-Xi'an high speed railway; a field test applying a 6% cement in mix ratio has been conducted to study the construction techniques and the testing method on reclamation and compaction. By applying the different compaction methods on different thickness of this filling material, the optimum roll-on method, optimum roll-on frequency and correlated controlling parameters have been identified and this provides the references on control indexes for the subgrade construction. The compaction quality was examined against both physics and mechanical indexes and the factors affecting the compaction quality were analyzed. The optimum compaction testing method and the correlation between different control indexes revealed from this test in turn further provided the supporting evidence for this technique and its quality. Finally, based on the long term observation of the settlement and the forecasted after-construction settlement in hyperbolic, a comprehensive assessment has been concluded on cement improved loess regarding to the stability of the subgrade and its suitability as the filling material for high speed railway.