UCS Experiment And Microscopic Mechanism Of Modified Seashore Soft Soil Under Freeze-thaw Environment

In order to solve the defects of insufficient strength and large deformation of the soil mass of underground structures in seashore soft soil stratum,measures such as cement reinforcement and artificial freezing technology are generally adopted in engineering.However,the cementreinforced seashore soft soil is less and less able to meet the needs of engineering strength.The use of artificial freezing technology will change the properties of coastal cement soil.Therefore,20 % nano clay(NM)and 10 ‰ polypropylene fiber(PPF)were added as additives to the seashore soft soil with 20 % cement and 80 % water content to study the UCS characteristics of the modified seashore soft soil at different ages in non-freeze-thaw environment and the UCS characteristics of the modified seashore soft soil in freeze-thaw environment.At the same time,the micro-mechanism of the modified coastal cement-soil was analyzed,and its mechanical weakening effect was analyzed.The combination of micro-test and macro-mechanical test makes the research results more meaningful.The main contents and achievements of the study are as follows:(1)The UCS mechanical properties of modified coastal cement-soil under non-freezethaw environment at different ages(7d,10 d,12d,14 d,17d,22 d,28d,56d)were studied.The UCS of NM modified seashore cement soil is larger than PPF modified seashore cement soil at the same curing age under non-freezing and thawing environment.In addition,at the same age,after adding 20 % nm,the UCS of NM-modified seashore cement soil is 70 % ~ 85 % higher than that of seashore cement soil.After adding 10 ‰ PPF,the UCS of PPF-modified seashore soft soil can be increased by 10 % ~ 15 %.From this,it can be seen that both NM and PPF can improve the strength of seashore soft soil,and NM can obviously increase the strength of cement soil,and the effect is better than PPF.(2)The UCS mechanical properties of the modified seashore soft soil with 7d curing age under freeze-thaw environment were studied under different freeze-thaw times(3 times,5 times,7 times,10 times and 15 times).The test results show that the stress-strain curves of the modified coastal cement-soil under different freeze-thaw cycles are strain softening curves with obvious peaks.The freeze-thaw cycle has a deterioration effect on the strength of the modified seashore soft soil,and the deterioration effect mainly plays in the early stage of the freeze-thaw cycle.With the increase of freeze-thaw cycles,the deterioration effect begins to weaken.While the sample is under the deteriorating environment of freeze-thaw cycle,the cement continues to hydrate to improve the strength of the soil.(3)The UCS of modified seashore soft soil in freeze-thaw environment is smaller than that in non-freeze environment.At the same freeze-thaw times,the UCS of PPF-modified seashore soft soil is larger than that of NM-modified seashore soft soil on the whole.At the same curing age,the mechanical weakening effect of PPF modified seashore cement soil in freeze-thaw environment is less than that of NM modified seashore cement soil.It can be seen that PPF has strong frost resistance,while NM has weak frost resistance.(4)SEM microscopic test analysis was carried out on the modified seashore cement soil samples with the curing age of 7d,and EDX microscopic analysis was carried out on some of the samples.Analysis of microscopic test results shows that the inner density of NM-modified seashore cement soil is greater than PPF-modified seashore cement soil in non-freeze-thaw environment.The degree of cementation and densification in the micro-image of the modified coastal cement-soil under freeze-thaw environment are both low.