Study On Deformation Property And Stability Technique Of Widened Embankment Of High-Grade Highway

As the developing of our country's economy with sustained, healthy and rapid speed, the highway construction of our country has made tremendous achievements. Until the end of 2006, the total length of china's highway had reach 3.48 million kilometers, the expressways is 45,400 km, maintained second place in the world, with 10 years to complete the developing process that the developed country need 30 to 40 years to complete. In recent years, with rapid economic developing, the vehicles retaining is significant increasing, some highways is difficult to adapt to the growing volume of traffic and need alterations, expansions and improving its technical level. It can effectively reduce traffic pressure and traffic accidents, improve road traffic capacity. But in the road expansion process, the problem of the subgrade widened, especially widen embankment deformation properties and stability has become increasingly prominent. Highway widen project will be problem that our highway construction must face and urgently settle at the beginning of this century. This paper, aim at the key technical issues of the highway extension project, combined with the TongJiang to Sanya Highway FangZheng to Harbin widen project, employ the site tests, numerical simulation and theoretical analysis, etc methods, carry out systematic study on the deformation behavior and stabilized technology of the new and old embankment, mainly contents and conclusions are as following:(1) Bonding actual project selected representation section, carry out detailed geological investigation on the representative section. Experimental investigation showed that consolidation of the old road had basically completed through long-term use. The engineering properties of the soil, which is in the superficial layer of the new and old subgrade, had obvious difference. The old subgrade foundation load acted, the physical and mechanical indicators had different levels increase compare to the new widening foundation, particularly compressibility and intensity indicators are higher than the new subgrade foundation, the deep level changed not obviously. (2) Employed the non-linear finite element analysis method, which is based on the elastic-plastic constitutive, studied the deformation characters and influencing factors of the interaction between the new and old embankment, when the new road is under the grading loading process. Calculation showed that the convergence method of the old and new embankment, the physical and mechanical properties of the filling materials, and the application of geodetic grid would affect the deformation and stability of new and old subgrade to different degrees. Widening in the same width, on both sides broaden methods had an obvious advantage than unilateral widen possess. In different embankment height, biggest vertical deformation on the table of the old subgrade, the minimum vertical deformation, the biggest deformation differences are significantly increased when the embankment height increases. In smaller embankment height, vertical deformation and deformation difference increased faster, with the further increase in high embankment, the growth of deformation is slower. When the new embankment height is increased, the largest settlement point on the surface of the widen subgrade gradually move to medial. The new subgrade significantly influences the horizontal displacement of the surface, particularly the horizontal displacement of the old subgrade, and tract to the both sides from the largest settlement point. The biggest vertical deformation on the table of the old subgrade, the minimum vertical deformation, and the biggest deformation differences are not significantly increased when the elastic modulus of new embankment filling soil is increased. When volume of the embankment filling soil is not altered, the modulus of change on the impact of the old embankment settlement could be ignored. But increase the modulus of the new subgrade soil can effectively reduce the compressive deformation of the new widen embankment. When the modulus is low, increased modulus had greater impact on deformation of the new embankment, with the modulus increasing, the impact gradually ice. The maximum vertical displacement of the new embankment continuous increased in direct proportion when the density of the embankment material increased, respect for each additional 1KN/m3, and an average increase of 5.5% settlement. The c,φvalue of the filling have a definitive influence on settlement of the new embankment, when the c,φvalue is lower, the influence is larger, with the c,φvalue increased influence gradually ice. The location and the different layers in the new subgrade of the geodetic grid had smaller impact on the deformation of the new and old embankment, reinforced ineffective.(3) In cutting and excavation process, when the slope excavation and slope cutting of the old road is smaller, have smaller influence on the vertical deformation and horizontal deformation of the old embankment, and is more favorable for the stability of the old subgrade. In the course of filling the new embankment, after several ways of slope cutting and excavating, the new embankment filling had a significant impact on the vertical displacement and lateral displacement of the old embankment, the greater volume of loading, vertical displacement and lateral displacement value are greater. Excavation and filling superimposed at the same time, the influence of the small stage program on the vertical deformation and lateral deformation of the old embankment is basically same. Excavation methods recommended level: slope cutting first, the thickness is 30cm, the stage excavating, and the stage dimensions: height is 80~100cm, width is 100~150 cm. Through the calculation and analysis, we can see that the old road injury and destruction is in step with the new excavation unloading and the widening filling loading, two stress and strain distribution formation the dynamic damage and destruction, therefore should minimize loading and unloading volume.(4) Used the strength reduction finite element analysis method to carry on systematic study on the stability of the widen embankment, used limiting equilibrium method to calculate the slope stability coefficients, and compared the result of the two method. Research shows that, using the strength reduction finite element method to calculate slope stability coefficient had obvious advantages, and is reliable. Results show that: the most dangerous slip surface of slope actually is not a function can be described by a simple curve, but slip bands with a certain width. Proposed the criterion for slope instability: have a sharp increase of deformation on the curve that maximum displacement of the slope crest with strength reduction coefficient changes, and have a plastic piercing district. At this point, take the strength reduction coefficient as safety factor to the overall stability of the widen embankment slope has a clear physical meaning. With the height of subgrade increasing, the stability safety factor of widening embankment slope decreased gradually, in small subgrade height, the safety factor decreased rapidly, with the height of the subgrade ever-increasing, the safety factor decreased gradually ice. With the density of embankment filling ever increasing, slope stability safety factor take the declining trend with a straight line, respect for each additional 1KN/m3, safety factor dropped3.03%. The shear strength c value of the embankment filling soil has little effect on the stability,φvalue of the embankment filling soil have no impact on slope stability. The reason is that the new widening embankment is basically in the forecasted slip surface, its strength not been fully exploited. Set up the gentler slope or employ the slope form, which has verge, can significantly improve the overall stability of the embankment. With the density of soil increasing, the slope stability and safety factor of the embankment is also increasing, but the rate of increase is slow. With the soil shear strength c,φvalue of the embankment constantly increasing, the slope stability and safety factor of the embankment is also increasing, and the rate of increase is rapid,φvalue is more prominent.(5) Monitoring test and analysis results of the representative cross-section showed that with the height of the new widening embankment growing, embankment load is increasing; the magnetic ring segregated settlement also will be continually growing, under the same load, the more close to the top, its corresponding increases value in the settlement is greater, the settlement value is also the largest, the vertical deformation of subgrade and foundation is mutually integrated with the corresponding layered filling loading. After filling embankment, settlements of each floor move slowly and toward stability, the settlement of new embankment verge was higher than that of the old embankment verge (central reserve after widening), and deformation of the magnetic ring in the old embankment is rather close, the deformation of the magnetic ring was significant smaller than the magnetic ring that in the new embankment verge, after the embankment filling, further deformation was small, foundation was in a relatively stable state. Lateral displacement is growing with loading of soil filling, the more rapid the soil filling, the more rapid lateral deformation growing. To the toe of the new road, the biggest shift occurred in certain depth, the largest displacement was related to the soil thickness and strength of the foundation. To the section that is under the old road verge, influenced by interaction between the new embankment and old one, and new and old subgrade were in a very stable condition, the maximum displacement occurred in the 0 ~ 0.5 m range upper part of the old road. In embankment filling, the pore water pressure was significant increased when the load was increased, the faster loading rate, the greater the load, the faster the pore water pressure increased. After loading, the pore water pressure had a significantly dissipation process. Some time after loading, the pore water pressure dissipation ease gradually, then to be stabilized. In the layered filling construction process of widen embankment, basically, the earth pressure increased with the construction load increased, in the same stage of construction fill loading, the earth pressure near the center of the widen road the new embankment increased more the earth pressure near the slope.(6) Use the monitoring data, employ standard method to analyze stability control of the typical section in the engineering example, the results show that the largest land settlement rate and the largest lateral displacement rate of the three section did not exceed the norms that standards set, show that the subgrade is stable in the widen embankment construction process. The time that the largest land settlement rate and the largest lateral displacement rate occur is the same that loading rate is the most high in the filling construction, the two are identical.The innovations in this paper are the following:①In the process that employ the non-linear finite element analysis method, which is based on the elastic-plastic constitutive, apply the stress balance means to achieve the initial state that the displacement of the foundation and the old Road is zero, on the base of that, adopt classification loading to simulate construction process loading, take the finite element calculating results closer to the actual project;②Through compare and analyze the methods of slope excavation slope and cutting in the old embankment, promote reasonable program, and promote the viewpoint that the old road injury and destruction is in step with the new excavation unloading and the widening filling loading, two stress and strain distribution formation the dynamic damage and destruction;③Establish the relation which is between the widen embankment deformation , widen embankment stability and the embankment height, embankment filling parameters, foundation parameters, then promote corresponding suggestion which can decrease the deformation and improve slope stability;④Promote the viewpoint that the most dangerous slip surface of slope actually is not a function can be described by a simple curve, but slip bands with a certain width, the shape and location of the slip bands are same with the largest displacement contour and plastic strain concentration area;⑤Proposed the criterion for slope instability: Have a sharp increase of deformation on the curve that maximum displacements of the slope crest changing with strength reduction coefficient changing, and have a plastic piercing district, this slope instability criterion have a clear physical meaning.In short, this project through accumulate large amounts of data, information and calculation results, would surely provide a reliable theoretical basis to the design and construction of highway widen project, have an important guiding significance for enhancing the quality of old road widen project, reducing highway disease. Research results have an important guiding significance for improving the construction standard of expressway widen project, the benefits of social and economic are significant.