Mechanisms Of Differential Settlement Of Widened Embankment And Its Treatment By Geogrid

With the rapid development of economy, volume of highway traffic increasesquickly. A considerable number of expressways in service no longer satisfy the needfor both increasing traffic volume and social progress. Widening the existingembankment is the effective way to solve the problem. The consolidation time isdifferent between the widening and existing embankment. On the other hand, thedistances from the gravity of widening embankment and addition lane load aredifferent between the widening and exiting embankment. It makes that the increasesof effective stress and pore pressure are different between the widening and existingembankment. Differential settlement develops between them. It is important toknow the mechanisms of differential settlement for treating it. Two-dimensionalfinite element software ABAQUS is used to investigate stresses and deformations ofthe widened embankment. The Mohr-Coulomb model, the pore/plane strain element,the soil step, the transient analysis are used to analysis the mechanisms. Thesurface-to-surface contact is used to simulate the splice of the widened embankmentand exiting embankment. And then the factors that influence the differentialsettlement of widened embankment are analyzed. Finally, the mechanisms of thetreatment by geogrid are analyzed. The main research content and program are asfollows.First of all, it is verified that using the surface-to-surface contact to simulatethe new and old embankment contact interface is feasible. Compared with usingcontact for the simulation of new and old embankment surface interaction, thedifferential settlement value by means of tie is bigger in the construction phase ofthe new road, and they are matched after the operation of the road. And the relevantvalue by tie connect is smaller after the nine years of operations. The shear stress ofupper embankment by tie connect is greater than by contact.Second, compression deformation of soft ground is the leading cause ofsettlement. During the construction of the new road, when it begin to operate andwhen its operation time is nine years, the differential settlement values produced bythis layer accounting for the deformation of the entire maximum differencedeformation are55.8%,50.8%,62.3%, respectively. When new road is completed constructed, the transverse gradient change on the embankment surface reaches themaximum, which is0.8%, however, that exceeds the tolerated transverse gradientchange in the shoulder. When the new road begins to operate and when theoperation time is about5.5years, the maximum transverse gradient changes of theroad are0.26%and0.24%, respectively. And it is prone to crack near the contactarea between the new and old embankment. Due to the distance away from theloading position, additional effective stress and pore water pressure generated aredifferent, which result in differential settlement mainly.Third, in this paper，with the increase of the filling height, the settlement of oldand new embankment gradually increase, the maximum transverse gradient changeincrease. But the differential settlement reduces slightly. With the increase of thewidth, the differential settlement increase. With the increase of the filling height,the settlement of both old and new embankment and the differential settlementgradually increase. With the increase of contact slope angle, the settlement of oldroads are almost the same, the settlement of new road is gradually increasing. So thedifferential settlement and the maximum transverse gradient change increase. Thelocation of the largest settlement, with the contact slope angle increasing, graduallymoves toward the new embankment toe. When the overlap slope angle is1:1, thelargest settlement is in the new road shoulder. Both unilateral and bilateral broadencases have little impact on the settlement of the old road, however, unilateralbroaden case has greater influence on the settlement of the new road than thebilateral broaden case.Fourth, the laying of geogrid can effectively reduce the settlement of the newroad, so that this method will reduce the differential settlement, however, the effectis small. This measure has a demonstrable effect on controlling the lateraldisplacement of the embankment slope. With the number of the geogrid layersincreasing, the differential settlement decrease, the slope lateral displacementreduce. Laying geogrid decreases the vertical stress passed beneath it. And it alsoreduces the shear delivered to the foundation. The more layers of geogrid, the moreeffective of this change function. A range of geogrid close to the slope has no force.The geogrid laying in the bottom needs larger intensity, while one laying in theupper needs smaller intensity. By this way, the geogrid can give full play to theirstrength. It is economical and practical that the position2.5m close to new road shoulder don’t lay geogrid on the upper layer.