Research On Settlement And Deformation Characteristics Of Peat Soil Roadbed

With the high speed development of our country economic, it may be said to bechanged with each new day for highway construction development. Much manynew-constructed highway inevitably pass through peat land sections, at present theconstructing freeway only in Jilin Province from Jiang Mifeng to Hunchun just hasmany. Through investigation on behavior to the completed and used highway in peatland district, we discover that roadbed has been great settlement and engendered a greatdeal of disease caused by the extruded the basis of roadbed such as lateral sticking outor cuting crack to squeeze out, roadbed sliding caves in, heave frost, road surface netcrack and so on. These facts indicate we could not master deeply the naturalcharacteristics of peat soil yet and lack effectual measures to diseases. So it is muchtheoretic significance and practical value to research on the characteristics of peat soil.Through of all-around field survey to peat land, original location testing and muchmany core sample examinations, we draw the important conclusions that peat soil hashigh water content, high organic content, high hole ratio, high compressibility, highheave and low shearing strength. For this, we do many experiments, including (1)bulkspecific gravity experiment;(2)moisture content experiment;(3)sizing test experiment;(4)plastic and liquid limit experiment;(5)density of soil particles;(6)loss on ignitionexperiment;(7)direct shear test;(8)permeability test;(9)convention compressive test;(10)high pressure solidifies experiment;(11)microscopic structure analytical test;(12)mineral ingredient analytical test;(13)organic content analysis and PH valueexperiment;(14) 14C determination peat soil age experiment;(15)peat soil not rottenroot system experiment. At the same time, we carry on analysis to the microscopicstructure and mineral ingredient and stratum age determination of peat soil under thedifferent pressure function by using the advanced transmitted light entity microscope, Xbeam diffraction technology as well as 14C method. These provide technic theory byscientific and credible indexes or parameters for getting feasible measures.In view of the seasonal freezing climate in the northeast area, we get researcheddeeply to the freeze heave feature of peat soil for the first time, which belongs to bestrong freeze heave earth, and grasp the freeze heave and friendly sank rule of peat soilunder different water content and load function (simulation roadbed reclamationaltitude). It provides foundation for the analysis of freeze heave and friendly sank aswell as peat soil roadbed construction further optimal measures.Be based on ground distortion principle and subsidence and solidifing computationanalysis, the paper carries on theoretical analysis and forecast to the rule of peat soilground lamination subsidence and final settlement time-space variation by depending onthe experimental project representative sections exploration sample and core typephysics-mechanical testing achievement, and assured peat soil settlement deformationparameters. Through of theoretical analyses and comparison, we know that the totalvalue of peat soil settlement increases along with peat ground thickness increasing inthe space, in which host-consolidation settlement and instantaneous subsidence aremainly included. Although the value of sub-consolidation settlement is small, itsproportion can increase along with argillaceous clay thickness to constitute soil layer siltincreasing, therefore, the time needed is longer for displaying in the subsidence. Thetheoretical result and actual monitor data fit well, and it proves that adoptive theoriesand parameters are appropriate. These instruct practical significance to design andconstruction.By the contrast theoretical analysis of peat ground to subside, the settlement andconsolidation of peat soil is very different when being dealed with in bigger thicknesssection with centain vertical draining water measures, such as adopting plastic drainingwater board or sand pile and so on. Especially, when used sand pile, the consolidation ofpeat soil obviously speeds up, and 20 day-long consolidation is equal to 120 day-longconsolidation of not being dealed with. It shows that there is important reference valueto actual project application.In order to comprehensivly grasp behavior in service of peat soil roadbed, wechose five routes 12 road sections in Spring and Autumn Period disadvantageous seasonto carry on disease diagnosis, and take this as the basis, in view of the road section notgood geology situation, in line with not destroying original condition of peat soilstratum to be advantageous for wetland protection, as well as enhancing roadbed theoverall stability and the anti-distortion ability, facilitating principle for construction, wecarry on the change to original design by computation, research and analysis, askingexpert to consult, to prove and to compare repeatedly. Then, we determine theeconomical and technical feasible measures, namely, to use certain measures such asusing light quality embankment, counter-pressure berm separately, reinforcedembankment, a grain of spur pile, gravel soft rock admixture strip and compound earthlabor cloth, partial elimination to fill in and so on. By this, we construct eight sectionsof experimental projects and install underground massive meters sign and carry on themonitors of the subsidence, the surface distorted, in-depth lateral displacement, waterlevel, earth pressure, pore-water pressure. At the same time, under the conditions offreezing season climate and driving moving-load function, we get to long-termobservation, key monitor as well as the sample investigation. After reorganization andanalysis to almost three-year observation data from the experimental project, we findwhat are as follows:(1) Completed value of settlement occupies that of total consolidation settlementfrom 85% to 97%, the proportion is quite high. It has positive significance to enhancethe stability of work done.(2) Through monitoring analysis to peat soil ground section (roadbed cross section)deformation under embankment reclamation load function, the paper establishs highfiduciary level conic envelope curve model of roadbed cross section subsidencedeformation and discovers that conic envelope curve is steeper when using directreclamation and eliminating trading to fill in gravel plan. Namely, the uniformity levelof deformation in roadbed cross direction is lower.(3) In construction, peat soil ground subsides and sticks out along with the timeoccuring in turn at the flank foot of embankment, appearing undulation situation. Thepeak value of settlement and sticking out has the direct ratio to peat soil thickness.General deformation is in the elasticity in the scope, and the biggest subsidence orsticking out of individual cross sections is from 10cm to 20cm. This should be arousedattention.(4) The project implementation effects the underground water level of peat soil tosome extent. But after the climate control function of the second freezing and springmelting, the underground water level has the rise trend.(5) Under the function of embankment load, peat soil roadbed brings obviousvertical additional stress, whose value is in 1.0~1.35 time of scopes, also increasingalong with the load increasing;The additional stress produced by temperature changingis higher than the load additional stress, namely, the additional stress near road shouldertwo sides is obviously bigger than that near road center, in view of this, the additionalstress produced by peat soil under roadbed could be speculated to be in their period.(6) Along with roadbed reclamation increasing load function by the level, peat soilground pore-water pressure will increase, which can unceasingly dissipate along withthe time;The pore-water pressure agglomeration and dissipa ting will bring obviouschange because of temperature change and moisture migration which can pass throughthe whole peat soil in the depth scope.(7) Peat soil internal pore-water pressure will appear obviously steep rise or rapidfall for load and environmental effect when used the counter-pressure berm, the earthlabor grill and the direct reclamation;If used gravel soft rock mix-filled strip andcompound earth labor cloth and sand pile, peat soil ground pore-water pressure willpresent relatively calm undulation;If used plastic froth block (board), peat soil groundpore-water pressure on 1.0~1.3m shallow layer will get less effect from load andenvironmental, and it will dissipate ruledly on 2.5~4m deep layer.(8) Peat soil ground vertical additional stress is affected less by vehiclesmoving-load, whose increasing value is only 0.10~0.92%, namely not to 1%. Thechange of pore-water pressure in freezing period may be neglected when compared tothe effect of vehicles moving-load. Thus, it proves that this season climateenvironmental effect is important factor to cause the change of peat soil ground stresswith these measures.In brief, in view of peat land district highway roadbed diseases, combiningdepending on the project, through diagnosis, room inside and outside experiments,theoretical calculation analysis, especially through different load function of measuresand seasonal freezing climate effect, the paper carries on monitors including peat soilground settlement, surface deformation, in-depth lateral displacement, water level, earthpressure and pore-water pressure and so on. The paper innovation spots are as follows.(1)For the first time, the paper opens out the project and freezing heave characteristicsof peat soil;(2)Depending on the experimental study of eight kinds of differentmeasures road sections, the paper brings forward peat soil ground stress anddeformation stable rule under the condition of load function and seasonal freezing effect,which establishs theoretical basis for enhancing the overall stability of roadbed in peatsoil area. (3)The new light quality separating warm material is used in peat soil roadbed,that obtains good effect;(4)Highway roadbed corresponding punishment measures inpeat soil area are put forward as important breakthrough and one of innovation spotswhich the paper obtains. Moreover, the research accumulates massive materials andsurvey data, which will provide certainly reliable theoretical basis for highway designand construction in peat soil area. It has important guiding sense for avoiding highwaydisease in peat soil area. The research results have important guiding sense to raisehighway construction level of peat soil area, of which social economy benefit will beremarkable.