Research On Early Warning Technique For Highway Landslides Or Slopes Reinforced By The Anchor-Cable And Frame Beam

Since the implementation of western development strategy,highways have developed rapidly in Shaanxi province.Because of the complex topographic features and geological conditions of the Loess Plateau in Northern Shaanxi and Qinba mountainous area in Southern Shaanxi,a large number of ancient landslides and new landslides caused by construction are distributed along highways;therefore,the stability of treated landslide(slope)sections has become the key factor affecting the safe operation of expressways.The anchor-cable and frame beam as a new type of supporting system has been widely applied to landslides or slopes along highways,but its theoretical research is far behind the engineering practice.And researches focused mostly on the calculation of internal force,design,the numerical simulation and model test,so the research on early warning criterion was few.In this paper,we take typical treated landslide(slope)sections along highways in Shaanxi province as the research object,and the lithology and actual failure form of the anchor-cable and frame beam as the basis,then we divide the early warning criterion into the criterion of anchoring force and displacement of frame to study.And the criterion of anchoring force can be divided into ultimate pullout force and anchoring force threshold criterion.Based on the design theory,we derive and fit out the formula of anchoring force threshold and displacement threshold of frame,so as to establish the early warning criterion,and verify the rationality of the criterions by examples;refer to the "demonstrated project",we propose monitoring and early warning technique for treated landslides along highways.The following achievements were obtained:(1)Refer to the traditional formula of the ultimate pullout force of anchor-cable,we established the corresponding early warning criterion;based on the Winkler foundation model and Pasternak foundation model respectively,under the condition of same anchoring forces,we determined the relationship between the position of maximum bending moment and the critical length of cantilever end through research,and used the software to fit out the formula of the critical length,then deduced the formula for calculating the anchoring force threshold;in the case of different anchoring forces,according to whether the position of maximum anchorage force could be determined or not,we studied on the calculation method of anchoring force threshold by two cases to obtain the corresponding early warning criterion.(2)Based on the Winkler foundation model and Pasternak foundation model respectively,under the condition of same anchoring forces,we derived the relationship between the displacement of frame and bending moment,and took the minimum displacement of the nodes of the end and middle of the beam as the displacement threshold;in the case of different anchoring forces,we fit out the relationship between the displacement threshold of frame and maximum bending moment,coefficient of subgrade,(shear modulus),the elastic modulus of concrete and other parameters,so as to establish the corresponding early warning criterion;through the comparative analysis of criterions based on the two models,we found that Pasternak foundation model was more appropriate for early warning and forecasting of landslides or slopes.(3)For the landslides reinforced by the anchor-cable and frame beam,we put forward the corresponding monitoring schemes,and the layout of monitoring points of the anchor-cable and frame beam;based on the monitoring schemes of landslides or slopes,we proposed the evaluation indexes of landslides(slopes),and established the early warning levels of treated landslides(slopes)along highways,which were the level of yellow,orange and red,and then we gave the corresponding countermeasures.