| Based on the existing research results, the concept of soil structural yield pressure is carried on a thorough analysis and systematic summary, and some new understanding is put forwarded, too. The action mode of ring-wall friction in the consolidation container is analyzed and a kind of floating type consolidation container is designed for carrying the contrast test to analyse the ring-wall friction’s influence on samples’ compression deformation. Further, some compression tests based on time-effect phenomenon are designed to verify the deformation state theory and to find the structure yield stress. Also, a new method to determine the thickness of compressible stratum by comparing the size relationship between structure yield stress and the foundation’s total load is preliminary studied:(1)Structuredness is the reason why soil shows properties of solid materials, which is especially obvious in medium-low and low compressibility soil, and this phenomenon make undisturbed soil and remolded soil has structure yield stress. In undisturbed soil, the structure yield stress includes preconsolidation pressure, structure strength and compaction-strength increment. In remolded soil, the structure yield stress includes precompaction pressure and compaction-strength increment. The structure yield stress is a kind of characteristic strength, which has remarkable influence on the development law of the compression deformation of test soil.(2)Because compression test is in state of completely confining conditions, the soil deformation will finally in convergent state. Using the structure yield stress as threshold value, the compression deformation state can be divided into fast-convergent state and slow-convergent state. Based on the size and variation features of fitting power, compressibility and compressive modulus, which is calculated by deformation under additional stress, the deformation state can be well distinguished.(3)The difference of action mode of ring-wall friction in the two kinds of consolidation container and their influence on samples which are in different pressures and compactness are analyzed by analyzing the deformation difference and relative error of compression deformation. The analysis shows that:Using floating type consolidation container can significantly reduce the disturbance of ring-wall friction. Compared with the ring-wall friction’s unidirectional distribution mode on the lateral surface of the test sample, that one in floating type consolidation is in a symmetrical distribution mode, which makes samples has more evenly force, lager size of deformation and be closer to mechanical condition of ideal compression test.(4)In order to reduce the distribution of ring-wall friction in traditional stationary type consolidation container, a kind of floating type consolidation container is designed. Also, four groups standard laboratory consolidation tests are carried by using different kinds of remolded silty clay samples which are in different compactness, and all of these samples are in saturation condition when the tests are carrying. The results show that:Load level and compactness of samples are closed to the interference degree on compression deformation by ring-wall friction. The cumulative compression deformation difference of samples which is between the two kinds of consolidation container grows as the pressure increases, but for the deformation relative error is opposite; the cumulative compression deformation difference and relative error of samples grow as the compactness increases, however the changes are not obvious in high range of compactness. Consolidation tests which using hard soil and low pressure will be significantly affected by ring-wall friction, the relative error can even reach about 20%.(5)In order to verify the deformation state theory, some compression tests based on time-effect phenomenon are designed. The test results show that:The compression deformation grows as the load becoming heavier, and the time-effect becoming obvious, too. If on the "curve shapes discriminance" view and described by law of the power n as it change with load level(additional stress ratio λ), the compression deformation state can be divided into fast-convergent state and slow-convergent state when using the load level λ= 20%～30% as threshold value. Of course, the test sample is in the state of completely confining conditions. Further, when λ≤20%, there is n≥ 2, and the state can be described as fast-convergent state when using "power discriminance". Otherwise, if described by the compressibility αV and compressive modulus ES, which is calculated by deformation under additional stress, the change law of two parameters become obviously different around λ= 20%～30%. If in bigger load level, αV become bigger fast while ES become smaller fast as load level growing. But, if in smaller load level, they tend towards stability. Further, when λ≤20%, there is αV< 0.1MPa-1 and the test sample show a low-compressibility characteristic. The deformation is small and finished soon. So, here can regarded the soil in this compressibility as fast-convergent state. To sum up, λ = 20% can be used as upper limit of threshold value and λ= 30% can be used as the lower limit of threshold value, which is to divide the deformation state.(6)The inner relationship between structure yield stress and deformation state is analyzed and a new method to determine the thickness of compressible stratum based on structure yield stress is preliminary studied. The results are that:For medium-low and low compressibility silty soil in saturation condition and normal consolidation, when the additional pressure is no more than 0.2 times the precompaction pressure, the deformation shows few time-effect, and the load threshold value is namely structure yield stress. As the post-construction settlement of subgrade design is a kind of time-effect of deformation, judging the size relationship between structural yield pressure and total load of foundation, determine the no time-effect stratum, where structural yield pressure is larger than total load of foundation, as thickness of compressible stratum. This method make the calculation of post-construction settlement by the thickness of compressible stratum has more explicit physical meaning. |
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