Deformation Properties And Settlement Control Of Peaty Soil With High Degree Of Decomposition

Peaty soil is a special soft soil with high moisture content,high compressibility and high organic matter content.Deformation analysis and control of peaty soil foundation is one of the technical problems in engineering construction.The physical and mechanical properties,the treatment effect of surcharge preloading and of the calculation method of consolidation deformation of peaty soil with the high degree of decomposition from Dianchi lake are studied by the combination of laboratory test and theoretical analysis.Main research works and conclusions are as follows:(1)According to the test results of conventional soil properties and referring to the Von Post Classification method,the peaty soil of Dianchi lake is classified.Using Micro-test technology,the structure and mineral composition of peat soil microstructure are determined.Microscopic pore distribution of peat soil contains mainly three aspects:the aerial large pore among aggregates,micropore in micelle or aggregation,the large size of pore in plant fibers;The main secondary minerals is mica while montmorillonite is fewer and main primary mineral is quartz.Carbon may come from the products after the decomposition of organic matter.(2)According to the compression creep test results,peaty soil has a certain structure.Compression index Cc and initial moisture content wo meet certain empirical relationship.The secondary consolidation coefficient Ca is much higher than that of non-organic clays,and the Ca/Cc ratio is 0.051,which is in line with the existing research results(0.05～0.06).(3)The variation law and main influencing factors of permeability coefficient were studied by consolidation permeability test combined with MIP test results.e～lgk,,curve is approximately linear.The empirical relationship between the ratio of the permeability index CK and the initial pore ratio e0,shows that this empirical formula(Ck/e0=0.25)is not only suitable for the fibrous peat,but also for the peat soil with high resolution.(4)The strength characteristics were studied by undrained triaxial test.The peaty soil with high degree of decomposition has the structure,and the strength characteristics which consolidation pressure is greater or less than the yield stress is different.The critical state line of the peat soil is approximately linear,and the internal friction angle is much larger than the internal friction angle of the conventional soft clay.The ratio of undrained shear strength to consolidation pressure is not only higher than conventional inorganic clay,but also slightly larger than Fibrous Peats.(5)The effect of different surcharge pressure ratios,different preloading durations and unloading durations on the compression law The peaty soil with high degree of decomposition were studied by one dimensional compression test.With the increase of the effective surcharge pressure,the secondary consolidation deformation and the secondary consolidation coefficient decrease greatly after the overload removal,and the empirical relationship between surcharge pressure ratios and the secondary consolidation coefficient is obtained.For peaty soil with high degree of decomposition,the surcharge pressure ratio of the peat soil is 0.4.The preloading duration should be the standard of the completion time of the main consolidation of peaty soil under the surcharge pressure.(6)Using the modified upwind difference method and MATLAB mathematical software,the consolidation deformation law of peat soil is calculated and analyzed based on Gibson one-dimensional large deformation theory,and the distribution law of pore ratio and pore pressure in different depth of soil is obtained,which verifies the rationality of the theoretical calculation of the soil deformation.The effects of peat compression index of soil and permeability index on the dissipation rate of pore pressure and the deformation of peaty soil were analyzed.