| In this paper,we study the backfill of super-deep and super-narrow trench in combination with the relying project.At present,2:8 gray soil is more commonly used in engineering for backfilling the foundation trench,which has more disadvantages.The trench is prone to accumulation of stagnant water,which produces erosion and additional pressure on the underground structure,and its structural safety is a great potential problem.To address this problem,this paper proposes to use modified cement soil instead of 2:8 gray soil as the backfill material for super-deep and super-narrow trench,so as to solve the problems encountered in backfilling 2:8 gray soil trench.In this paper,a combination of theoretical,experimental and numerical analysis is used to investigate the mechanical and durability performance of fly ash-water glass composite cement soils in conjunction with the dependent projects,as follows.(1)To determine the influence of each external admixture on the mechanical properties and to reveal the optimal admixture amount of each component.In order to explore the feasibility of applying this composite cement soil in foundation reinforcement project,the unconfined compressive strength test of cement dosing cement soil at each age was conducted and analyzed;on the basis of this,fly ash and water glass were mixed alone to form single-doped cement soil,and the influence law of the type and amount of external admixture on its unconfined compressive strength was analyzed.Through orthogonal test,the influence law of cement,fly ash,water glass content and matching ratio on the compressive strength of composite cement soil was analyzed,and the optimal ratio of each component of composite cement soil was clarified and verified by test,and the optimal ratio of composite water stability material was obtained:9% of cement,12% of fly ash and 3% of water glass.(2)The durability of the composite cement soil was evaluated and compared with the common cement soil.The effect of the composite admixture on the impermeability of the cement soil was studied and analyzed,and it was concluded from the test analysis that the impermeability of the composite cement soil was significantly improved compared with that of the ordinary cement soil under different maintenance age conditions.The resistance to dry and wet cycles and the resistance to freeze-thaw cycles of the composite cement soil were studied,and compared with the common cement soil,it was concluded that the resistance to dry and wet cycles and the resistance to freeze-thaw cycles of the composite cement soil material under the age of 28 d was stronger than that of the common cement soil,and the resistance to dry and wet cycles and the resistance to freeze-thaw cycles of the composite cement soil were further improved with the growth of the maintenance age.(3)The microscopic properties of the composite cement soil were analyzed and the curing mechanism was studied.The effects of the composite admixture on the microscopic morphology and hydration products were investigated by SEM electron microscopy and XRD diffraction and compared with that of the ordinary hydrated soil,and the results of SEM electron microscopy showed that the composite hydrated soil could bond the soil particles more fully and fill the inter-particle spaces more adequately than that of the ordinary hydrated soil at different ages,and the XRD pattern analysis revealed that The content of hydration products such as C-S-H and Aft of the composite cement soil under each age is greater than that of the ordinary cement soil.Based on the microscopic characteristics analysis,the curing mechanism of composite cement soil was discussed and analyzed,and the interaction mechanism of cement hydration reaction,fly ash three effects and water glass catalytic and alkali excitation effects in the curing process of composite cement soil was clarified,which provided the theoretical basis for the improvement of macro engineering performance of composite cement soil compared with ordinary cement soil. |
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