Consolidation Characteristics And Microscopic Mechanism Of Composite Modified Coastal Soft Soil Under Freezing-thawing Cycle

Coastal soft soil is widely distributed in coastal areas,but it is not easy to construct on soft soil directly based on the particularity of soft soil.At present,the most commonly used method to modify coastal soft soil is to add cement.It is very important to study the compression deformation and deformation rate of modified coastal soft soil,and soil deformation and consolidation are inseparable,so it is necessary to study the consolidation characteristics of coastal soft soil.Considering that the temperature drops to below zero in winter and increases in spring and summer will cause freezing-thawing damage to the soil,it is of great significance to further study the consolidation characteristics of the coastal soft soil modified by composite materials under freezingthawing cycle.In this paper,the cement modified coastal soft soil(namely coastal cement soil(CCS))and other composite materials modified coastal soft soil include fly ash modified coastal cement soil with fly ash(CCSF)and nano clay modified coastal cement soil with nano clay.The consolidation compression characteristics of CCSN under constant temperature and humidity curing and freeze-thaw cycle were studied.At the same time,CCS,CCSF and CCSN were microcosmic tested to explain their microcosmic compression characteristics.The main contents and results of the study are as follows:(1)The consolidation compression characteristics of CCS,CCSF and CCSN with curing ages of 7d,8d,10 d,12d,14 d,16d and 18 d under constant temperature and humidity curing were analyzed.At the same curing age,the compression resistance of CCSF is better than that of CCS and CCSN.Since the compression amount,deformation rate and compression coefficient of CCSF and CCSN are all smaller than CCS,it is feasible to use fly ash or nano clay to improve the compression resistance of coastal cement soil.(2)The consolidation compression characteristics of CCS,CCSF and CCSN after freezing and thawing for 1,3,5,7,9 and 11 times after curing for 7d were studied.Under the action of freeze-thaw cycle,adding fly ash or nano clay into the coastal cement can reduce the final deformation of modified coastal cement and enhance its anti-deformation ability.Under the same number of freezing-thawing cycles,the deformation amount,deformation rate and compression coefficient of CCSN were all smaller than those of CCS and CCSF.It can be seen that the effect of modification of coastal cement-soil by nano clay was better.(3)The consolidation characteristics of CCS,CCSF and CCSN with different curing environment but same curing age were studied.The test results show that the deformation difference between freezing-thawed samples and non-freezing-thawed samples increases with the increase of freezing-thawing times,while the difference starts to decrease in the late freezing-thawing period.With the same total age,the compressibility and compression index of CCS,CCSF and CCSN under the action of freezing-thawing cycle are all larger than those under constant temperature and humidity curing,and the compression modulus is all smaller than those under constant temperature and humidity curing.When the total age is the same,the deformation amount,deformation rate and compression coefficient of the samples subjected to freeze-thaw cycle are all greater than that of the samples subjected to constant temperature and humidity curing.In the early freezing-thawing period,the damage to the samples was obvious,while in the late freezing-thawing period,the damage to the samples was weakened.The cracks of CCSF and CCSN after freezing-thawing are less than those of CCS,and the crack width is also smaller.(4)CCS,CCSF and CCSN before and after freezing-thawing were tested and their microcosmic mechanisms were analyzed.Microscopic tests showed that after freezingthawing cycle,SEM images of all samples showed that the particles of samples were relatively loose and the density degree was low.In consolidation compression test,the compressibility of freezing-thawed specimens is higher than that of unfreezing-thawed specimens.At the same time,EDS and XRD data of CCS,CCSF and CCSN before and after freezing-thawing were analyzed,and it was found that only a small part of samples lost their components after freezing-thawing cycle.The microscopic test results are fed back to the consolidation test results,which can better explain the consolidation characteristics of samples in different environments.