Study On Engineering Geological Properties And Settlement Of Turfy Soil In Seasonal Frozen Region

The paper mainly relys on the following four research subjects, such as the national science fund items"Study on the time effect of the properties of turfy soil in seasonal frozen region".Communications department items of Jilin province"Study on infiltrate concretion settlements and processes optimization of turfy soft soil roadbed in the local railway from Jingyu to Huinan "and "Study on the settlements of soft soil roadbed of expressway from Jilin to Yanji in seasonal frozen region".the sub-project of ministry of communications western subjects"Study on the deformation and stability of turfy soil roadbed in the test section of Heda highway".Based on the studyment of the cause and distribution of turfy soil and the quaternary geological in Seasonal Frozen Region, took the typical and widespread turfy soil region for example, systematically discussed the material composition and micro structural features,the statistical characteristics about physical mechanics property index,strength characteristics and compression characteristics, then put further research on the physical chemistry mechanical characteristics about the widespread turfy soil ground along ChangBai region in Jilin province and the come to the conclusion that it can provide sturdy and reliable technology basises parameters for feasible treatment.The engineering geological properties of Turfy soil summarized as follows:1.The turfy soft soil formation in ChangBai mountain in Seasonal Frozen Region maily in Three-Part-Structure, from top to down are turfy soil,mucky soil and gravel layer, which is the typical impact phase formation. Basted on finding out the soil of the roadbed, then do the test and put forward settlement calculation, the conclusions have wide guiding value for the similar roadbed research in the area. 2.The turfy soil in Changbai mountain area is quaternary holocene deposition soil with the features that new deposition, shallow burial depth and poor properties.The fundamental physical mechanical properties manifestations to be:high natural water content,the average water content is 324.5%; large natural density,the average density is 1.10 g/cm3, closed to water density; high compressible ,the average compression coefficient is 6.85 MPa-1,belongs to the high compressible soil. The natural density and specific gravity of the soil has the accrescented tendency with the depth increased, meanwhile water content,organic matter content,loss on ignition,porosity ratio and ph value all decreased.The study on the permeability of turfy soil shows that permeability present anisotropy as to the non-regular distribution of plant fiber in turfy soil, it is usually simplified into the differences in level and vertical.The basic unit of turfy soil is non-completely decomposed plant fiber which composed the framework,with the filling of humic substances and mineral colloids,just being aerial construction.The non-completely decomposed plant fiber compose the framework in the from of edge to edge,edge to face and face to face. Humic substances colloid and mineral colloid are in exiguous sphaerolitic,with aggregates and micro-aggregates filling in the macropore of the soil.The settlement is always the most important soil mechanics subject.In the coastl of china which soft soil is widely distributed,it has made massive research and obtained series of important results.The cause,distribution characteristics and engineering properties of the soft soil in north seasonal frozen region is very different form the coastl soft soil.The highway department in china made a less research of the settlement about the soft soil in northeast seasonal frozen region.This paper is based on the subjects about the soft soil in the seasonal frozen region,it includes the time,space,strata structure,drainage path,stress path and parameters,it makes a research about the settlement of soft soil roadbed in seasonal frozen region, which is expected to guide the local highway construction. It gains the the following results through the analysis of the settlement of soft soil roadbed in Seasonal Frozen Region:1.The initial freeze of the seasonal frozen in study area is generally in the October first ten days,the spring thaw is in April~May,the completely thaw is in middle of May.According to the ground temperature monitor data ,form December current year to the early April next year,the freeze depth is always above 1.5m.In 2004 winter the maximum freeze depth is 1.8m.It establishs the freeze model according to the freeze characteristics.2.In the previous roadbed settlement calculation,it always according to designed filling depth which loaded disposable.While in this paper,the load is gradually applied by grade.Considering this,so this paper uses the differential permeation coefficient and compression coefficient corresponding the load is applied by grade to calculate the consolidation coefficient in the calculation of the consolidation settlement.It makes a power function fitting through the permeation coefficient and the consolidation pressure,it solves the permeation coefficient under different load through the fitting equation;according to the load,it uses the per-grade load permeation coefficient in the e-p curve, which is expected to make the settlement is more close to the practical.3.It considers the well channel drains to square vertical drains,it researchs the settlement of the soft soil with the variation time according to the Terzaghi two-dimensional permeation consolidation theory, it's main reason is that they provide the same permeation path for the soft soil.The consolidation speed speeds up significantly after the traetment, it's main reason is the permeation path which provided by the high permeability soil&stone filled in the well channel drains to the soft soil,it forms the complete drainage system with the soil and stone in the surface and the coarse sand under the blew.4.Form the proportion of each stage settlement schematic diagram at K121+845 section it can be see that,the main consolidation settlement accounts for a large proportion.In the center of the road,the instantaneous settlement of the soft soil 10.707cm accounts for 25%of the total settlement 41.956cm, the secondary consolidation settlement 2.939cm accounts for less than 10%,the rest 70% is the the main consolidation settlement.Comparsion the settlement of differential strata, the turfy soil is 0.8m depth,the total settlement in the center of the road is 23.354cm, the silt soil is 1.6m depth,the total settlement in the center of the road is 16.135cm.For the foundation treatment which is main to decrease the settlement,it should be treat the two layers together.5.Form the K25+635 section , comparsion the settlement of differential strata, the turfy soil is 1.5m depth,the total settlement in the center of the road is 25.932cm, the clay soil is 7m depth,the total settlement in the center of the road is 30.036cm.For this situation the key is the treatmeat of the turfy soil.6.It researchs the settlement characteristics of soft soil with the variation time according to the Terzaghi permeation consolidation theory,the main basis is the different soft soil permeation path during the pre and post of the top soil frozen. The consolidation speed of the soft soil after the top soil's frozen is obvious solwly,the main reason is the soft soil loss the well permeation channel after the top soil frozen.In terms of engineering treatment measures, whether or not to apply directly in coastal region as in Seasonal Frozen Region and how to make an economical and feasible technical scheme need for further study and argumentation. Relying on construction projects and consulting the experts, this paper puts forward the treatment principle on turfy soil roadbed that based on poor geological conditions, under precondition of undisturbing turfy soil layers and protecting the wetlands and through the necessary settlement and stability calculation, the scheme follows concepts which are economical and reasonable in treatment measures, feasible in technology, and agreeable to specification indexes on settlement, stability design indexes, and environmental protection. This paper concludes the monitoring and evaluating results based on eight road sections treated by different measures in Heda Highway project and the well channel drains measure in Jilin-yanji Highway project. In addition, it analyze synthetically construction conditions, economy, technology, environmental protection and the likes, and puts forward roadbed suggesting treatment measures in seasonal frozen turfy soil regions for future similar highway projects as reference. Furthermore, it will raise the level on highway construction in seasonal frozen region, implement the harmony between human construction engineering and natural eco-environment, and promote the economic development in northeast old industrial base.As far as treatment measures in turfy soil region are concerned, there are some disadvantages that are high cost and environmental destruction, on the replacement sand-gravel measure commonly adopted in design, specially partly replacement.Direct filling measure adopted by low-class highway owner is not recommended, because it leaves behind hidden danger for highway settlement and stability, what is more worse, it will cause damage to environmental protecting in wetlands. The well channel drains measure is recommended by this paper in turfy soil region as well as sand-pile method which is adapt to thicker turfy soil region. And then some economical and feasible measures, such as the strengthening geotechnical grille, geotextile isolated drainage, and sand-pile methods enjoy advantages in terms of roadbed buried depth, roadbed filling height and construction period requirement, moreover, bring down the cost by 15%-25% by comparison with replacement sand-gravel method. In addition, plastic foam materials can decrease the cost, and remarkably when produced in local area.The main innovative points of paper:1.Through the collection of climate data and regularly observation of earth temperature, understand and master time characteristics and freeze deep of turfy soil roadbed in the seasonal frozen region, and establish frozen roadbed model. Based on the frozen roadbed features, from the stratum structure, drainage path, and other aspects ,researched the infiltration of consolidation mode of peat soil roadbed in different seasons, study on impact of seasonally frozen on consolidation and settlement of turfy soil roadbed. Predecessors in this area have not been involved, the rearch of this paper is now at the preliminary stage of exploration.2.The calculations of turfy roadbed settlement in seasonal frozen region were assumed an instantaneous loading to calculate consolidation settlement. Actually,it is different from the roadbed filling process. Based on the roadbed actual filling process, adopt consolidation degree theory of staged loading, with parameters of consolidation changed according to the loading gradually the, taking into account infiltration consolidation mode of the different seasons, to calculate consolidation degree of turfy soil roadedbed of typical tratum of different roadbed treatment in seasonal frozen region. Adopt the permeability coefficient and compression coefficient according to staged loading to calculat consolidation coefficient. It is certified that and the actual terms of the settlement of close monitoring of the settlement, the method used in the paper meets engineering requirements and is feasible.3.Through field inspections and investigations, based on cause and distribution of turfy soil and Quaternary Geology of turfy soil in the seasonal frozen region, relying on four research topics, taking larger scope of the peat swamp land area for delegates to a typical, systemly study the material composition and soil micro-structure characteristics, physical and mechanical properties of the target demographic characteristics, the strength of character and compression characteristics Study and summarize physical and mechanical characteristics of turfy soil of the Changbai Mountain area in seasonal frozen region, to enable it to provide reliable parameters and help to identifing practical treatment. In engineering geological characteristics of turfy soil, although some people regard some projects had concluded, this paper features involved in more project, on a wider scope.4.the study on forecasting settlement of turfy soil roadbed according to the field monitoring data are less.no previous comparative study on fitting methods of turfy soil roadbed settlement. In this paper, fitting methods of index curve, hyperbolic and Logistic growth curve are used to roadbed settlement fitting. And by comparation ,the use of hyperbolic fitting is the best method.