| The stability of highway projects in the northwest region of China decreases because it undergoes freezing and thawing every year.Road and bridge transition section is a weak part of rigid abutment and flexible embankment connection.Common road and bridge transition section diseases include road settlement,road pavement cracking,crushing,and water seepag.These diseases will cause jumping phenomenon,seriously affecting the driving safety and comfort.Based on this,this study carried out the following research on the loess in the transition section of Luojiagou Bridge Road in Maiji District,Tianshui City,Gansu Province:Firstly,the basic parameters of soil samples were determined by laboratory tests.Secondly,under the condition of optimal water content,the plain soil(SP)was improved by different cement incorporation ratios and steel slag incorporation ratios and unconfined compressive strength test was carried out.Then,under the conditions of optimal cement incorporation ratio and steel slag incorporation ratio,direct shear tests were carried out on the improved soil after freeze-thaw action,and the influence of different times of freeze-thaw action on the shear strength parameters of the improved soil were determined.Then,the stress-strain curve of the improved soil was fitted and analyzed based on the Duncan-Chang model.Finally,COMSOL Multiphysics,a numerical simulation software,was used to analyze the pavement performance of the bridge transition section under the conditions of different filling materials,filling thickness and vehicle speed.Through the above research,the results showed that:(1)Through unconfined compressive strength test,it was found that the improved soil has the maximum compressive strength when the cement content is 8%.After 7 days of curing,the compressive strength of the soil sample improved by 7.7 times compared with that of SP soil sample;when the samples were soaked in water for 24 h,the reduction amplitude of compressive strength was about 20.1%.When the steel slag content was 20%,the compressive strength of the modified soil was the highest.After 7 days of curing,the strength of the modified soil sample increased by about 1.6 times compared with that of the SP soil sample.Similarly,the compressive strength of the curing sample after 24 h immersion in water attenuated by about 53.5%.(2)Direct shear test under freeze-thaw action found that: Under the condition of curing for 28 days,the cohesion of cement improved soil(SP-C-8)decreased by 13.3% after one freeze-thaw cycle.After three freeze-thaw cycles,the cohesion of soil decreases by 18.3%compared with that without freeze-thaw action.After five and seven freeze-thaw cycles,the cohesion decreased by 22.1% and 23.5%,respectively,the internal friction angle changed similarly with freeze-thaw action.Under the condition of curing for 28 days,the cohesion of steel slag improved soil(SP-S-20)decreased by 15.6% after one freeze-thaw cycle.After three freeze-thaw cycles,the cohesion of soil decreases by 22.4% compared with that without freeze-thaw action..After five and seven freeze-thaw cycles,the cohesion decreased by 25.7%and 27.7%,respectively,the internal friction angle was the same.On the whole,the shear strength of the improved soil decreased gradually with the increase of freeze-thaw cycles,and the shear strength of the improved soil stabilized after 7 freeze-thaw cycles.(3)Through calculation in COMSOL Multiphysics found when the filling layer is improved soil,the settlement is less than that of SP soil sample filling layer,and the settlement of SP-C-8 filling layer is less than that of SP-S-20 filling layer. |
