Study On Mechanical Properties And Microcosmic Mechanism Of Haikou Gulf Facies Muddy Soil After Improvement

Gulf facies muddy soil is widely distributed in Hainan Island.It is gray-black and graybrown,contains more fine sand particles,has a slightly glossy incision,high toughness,and has a slightly pungent smell.With the accelerated promotion of the free trade port,the demand for infrastructure is also increasing.In order to solve the problems of extremely difficult pile formation and composite foundation failure caused by the muddy soil of the bay facies,the research on the reinforcement methods of the muddy soil of the gulf facies has become a new research.hotspot.In this paper,Haikou bay facies silt soil(Haikou Bay and Puqian Bay)is taken as the research object,and the engineering characteristics of Haikou bay facies silt soil are explored by means of laboratory experiments and numerical simulations,and two types of bay facies muddy soils are found.soil reinforcement.The cement commonly used in engineering is selected as the main reinforcement material,and nano-powder is selected as the reinforcement material.The mechanical properties and improvement mechanism of the improved muddy soil are explored by using methods such as unconfined compression test,PFC particle flow numerical simulation,and scanning electron microscope test.The main research contents and conclusions are as follows:(1)The strength of the two silty soils increases with the increase of cement content and with the increase of curing age.The growth rate is basically linear,and the growth rate is more obvious from 7d to 14 d.Among them,the peak stress of PCS(Puqianwan cement modified muddy soil)is 14% larger than the peak stress of HCS(Haikouwan cement modified muddy soil)45%;through linear fitting,the formula for the change of HCS and PCS with age under different cement content is obtained,and the most significant change of15% cement content is obtained through the fitting formula.(2)Through orthogonal experimental design,nano powder can improve the compressive strength of HCS and PCS.Moreover,the content of nano powder selected in this paper was 1.5%,2% and 2.5% on the strength of silty soil,which first increased and then decreased.The optimal ratio of HNCS and PNCS can be treated by range analysis A3B2C3,that is,20% cement content,2% nano powder content cured for 28d;Cement is the factor that affects strength the most;The maximum peak stress of HNCS is2196.3333 k Pa,and the maximum peak stress of PNCS is 2919.978 k Pa.Under the same cement content and curing age,the peak stress of HNCS was 16% higher than that of HCS under 2% nano powder content.The peak stress of PNCS was 24% higher than that of PCS at 2% nanopowder.(3)Relying on the completed unconfined compressive test,PFC2 D was used to simulate the particle flow numerical simulation to study the mechanical properties of cement-improved silt soil and nano-powder-cement-improved silt soil,and determined the fine parameters required for each model,and analyzed the relationship between numerical simulation and indoor test,and showed that the numerical simulation and indoor test results had a high degree of agreement through stress-strain curve,peak stress and failure mode.The three-axis shear test was simulated and predicted,the deflection stress-strain curve and the strength envelope were drawn,and the internal friction angle and cohesion were calculated: the cohesion c of HCS with 15% cement content was 503.04 k Pa,and the internal friction angle φ was 25.33°;The cohesion c of 15% cement PCS was 649.94 k Pa,and the internal friction angle φ was 21.96°;The cohesion c of HNCS was 717.11 k Pa and the internal friction angle φ was 21.05°.Under the optimal ratio,the cohesion c of PNCS is 909.08 k Pa,and the internal friction angle φ is 22.48°.(4)Microscopic analysis of silty soil,silty soil with 15% cement content,and silty soil with different nano powder content.The main conclusions are: the distribution of particles in silty soil in Haikou Bay is uneven,the pores are slightly larger,there are unevenly distributed independent particles,and the force between the particles is poor.The silty soil in Pavedian Bay has a dense internal structure and fewer holes.Both are flocculent,but PCS is more flocculent and more stable than HCS.The nano-powder and the C-S-H and C-A-H series hydrates that accelerate the flocculent formation of the hydration products of cement,and the flocculent fiber structure makes the connection between the particles tighter.When the nano powder content is 1.5%,there are more large particles in the block,slightly less flocculent structure,and slightly lower strength.When the nanometer content is 2.5%,there are too many flocculent structures,slightly fewer large particles,and the strength is also slightly lower.When the nano powder content is 2%,the flocculent structure and large particles are interconnected,with the highest strength and the best reinforcement effect.