Analysis And Evaluation Of The Structural Strength Of The Soft Soil In Tianjin Binhai New District Under Cyclic Loading

Soft soil is widely distributed in our country, and its engineering geological properties(such as high sensitivity, low strength and long consolidation time, etc.) are very special, making it difficult to use in practical engineering.With the development of the national economy and extending to coastal citiesgradually, the coastal areas of the study of soft soil made a deeper request, this situation puts forward a further requirement for the study of soft soil in coastal areas.Natural deposited soft soil has certain structural characteristicgenerally, due to the structural existence, the soil mass can be caused sudden failure when the strength of soil reaches a certain finger, which resulting in great harm in the project.This paper takes the structural soft soil in Tianjin Binhai New Area as the research object, mainly researches on three kinds of soil in the field, a comprehensive analysis of theoretical analysis and experimental results are conductedbased on the combination of soil mechanics and soil science. Then the mechanism of macroscopic mechanical properties is further explained by taking the microscopic structure characteristics as the breakthrough point. On the basis of analysis combined withqualitative and a more accurate quantitative method, the characteristics of the compression properties of structural soft soil and resilience unloading and re-compression characteristics were analyzed.The main conclusions are as follows:(1) There are obvious differences of the compression curve between remodeling and originalsoil samples. The compression curve of the original sample is sectional distribution and has an obvious inflection point, while the compression curves of the remodeling samples are more consistent, and there is no significant inflection point.The originalsoil samples have the structure yield stress, and when the overburden stressis less than structure yield stress, the compression rate of original sampleare smallerand less than that of the remodeling samples.When theoverburden stress is greater than the structure yield stress, the compression rate of originalsamplessuddenlyincreases, andthe deformation quantity increasesubstantially, the compression amount is greater than remolded samples and bigger than the remodeling samples.(2)Structural soils haves some structural strength. The initial consolidation pressure was determined by the reduction of the compression curve of the sample after reduction. And the compressive curves were used to determine the structuralyield stress of the original soil samples. The difference between initial consolidation pressure and the structural yield stress is the structural strength, and then the strength of the structure of the three soil samples was determined.(3)The compression curves of original samples and remodeling samples are consistent with the normal consolidation compression curves, and the compression curvesare consistent with the law of the change. Theresilience indexsuch as unloading ratio and rate, rebound index, compression modulus under different test plansare analyzed, the results show that the resilience of the original samples is stronger than the remodeling samples.(4) Combined with mercury injection test and scanning electron microscope, the changes of pore structure unit size, abundance and average distribution shape of the soil after compression were analyzed. The study provides a theoretical basis for the evaluation of engineering properties of structural soft soil under different compression resilience.Experimental analysis shows that: the porosity becomes smaller after the compression, and the structural unit changed from loose to agglomeratestatein the soil.The pores are compressed and readjusted, the number of pores is reduced, the large pores are transformed into the small pores, and the directional orientation is weakened, and the consolidation degree of the soil becomes higher.(5)The structural strength mechanism of the resilient and recompression of structural soft soil in Tianjin is analyzed by the combination of the resilience index, the consolidation stability time and the distribution characteristics of the pore region after the test.Resilience index in the design of the complexity of the increase in compression resilience weakened. The total compressive deformation of samples with long consolidation time is larger than the samples with short consolidation time. In the compression process, the main change is the large pore transformed into the small pore.