| The uneven settlement between widened and old subgrades is an unavoidable problem in the reconstruction and widening projects of expressways,especially for expressways in the Yellow River flood plain area in Shandong.On the one hand,the design height of expressway subgrades in our country is relatively high,generally exceeding 4 m.For such high subgrades,settlement is very easy to occur.on the other hand,the Yellow River flood plain area in Shandong stores a large amount of Yellow River alluvial silt.The formation of this kind of silt is closely related to the historic flooding and long-distance transportation of the Yellow River.Therefore,it has characteristics of high particle roundness,surface defects,difficulty to compact,and porous.When used as a subgrade filling material,it is difficult to guarantee the quality of the filled subgrade.Because it was the old course of the Yellow River and the modern Yellow River also passed through it,the groundwater level is generally high in the Yellow River flood plain area in Shandong.The porosity of the alluvial silt soil of the Yellow River makes it prone to capillary phenomena under this condition and affects the stability of the subgrade.In addition,affected by the minerals in the groundwater,the alluvial silt of the Yellow River also exhibits salt-alkaline characteristics,which can lead to the deterioration of the strength of the subgrade.To change this situation and alleviate the uneven settlement of the subgrade widening construction in the Yellow River flood plain in Shandong,the study carried out the physical,chemical,and engineering properties of the Yellow River alluvial silt.Based on a comprehensive analysis and fully understanding its characteristics,a widening construction method called the partial-priority subgrade widening method is proposed.This method includes the partial-priority subgrade filling method,the subgrade internal and external union monitoring method based on IG intelligent geosynthetics and Beidou system,and the subgrade deformation prediction method based on lightweight neural network.For the partial-priority subgrade filling method,its essence is to divide the filled subgrade into the outer priority filling part and the later filling part.The principle of the partial-priority subgrade filling method to reduce the differential settlement between the widened and old subgrade lies in the optimization of the effective stress path in the ground by the outer priority filling part and its back pressure effect.In the study,the optimization of the effective stress path was studied through numerical calculation,and it was proved that the partial-priority subgrade filling method can increase the stability of the subgrade.In the study,an analytical model of the asymmetric ground bearing capacity at the gap between the widened and old subgrades in the partial-priority subgrade filling method was established by the limit analysis method.On this basis,the improved radial algorithm is used to compare the ground bearing capacity under the condition of partial filling and horizontal layer filling.It is theoretically proved that the back pressure effect of the partial-priority subgrade filling method can improve the ground bearing capacity.In addition,the influence of different factors on the ground bearing capacity is studied by improving the radial algorithm.It provides theoretical guidance for the construction parameter design of the partial-priority subgrade filling method.In research,the G1511 expressway was selected as the field test subgrade filling section.Comparing the deformation of the subgrade in different test sections,proved the control effect of the partial-priority subgrade filling method on the uneven settlement of the widened and old subgrades.The partial-priority subgrade filling method attaches importance to long-term monitoring of subgrade deformation,so a union monitoring method of subgrade deformation based on IG intelligent geosynthetics and the Beidou system is proposed.Among them,IG is a strip-shaped intelligent geosynthetic material made of superconducting carbon black and high-density polyethylene-based on the principle of percolation,which is essentially a conductive polymer.When it is stretched,the electrical resistance of the IG can change regularly with its tensile deformation.This feature is called the tensoresistivity of IG.Using this feature,IG can be used as a sensing device inside the subgrade to realize distributed monitoring of the widened subgrade deformation while exerting its reinforcement function.To investigate the possibility of its large-scale application in the engineering environment,the study conducted a temperature influence test within the range of-20??40?,and explored the influence of the service temperature on the basic mechanical properties,tensoresistivity,and longterm mechanical properties of IG,and constructed the normalized resistance-strain calibration model of IG under the service temperature field,which laid the foundation for the improvement of IG deformation calculation and monitoring accuracy.In addition,the study also carried out accelerated degradation tests on IG under various adverse conditions such as high temperature,ultraviolet radiation,corrosive environment,etc.,and analyzed its anti-deterioration ability.It proves the environmental adaptability of IG in engineering applications.When the IG is placed inside the widened subgrade,there is a high-dimensional nonlinear relationship between its strain and the deformation of the subgrade.Therefore,the analysis of the IG deformation can indirectly reflect the health status of the subgrade and make a diagnosis of the potential diseases of the subgrade.To obtain the information on the deformation of the subgrade more directly,the Beidou base station was arranged as a settlement monitoring device in the key parts of the widened and old subgrade,and a union monitoring method for the deformation of the subgrade was constructed together with the IG.Compared with traditional instruments such as settlement plates and singlepoint settlement meters,Beidou equipment has greater advantages in monitoring accuracy and service time extension,which is beneficial to long-term high-precision monitoring tasks.In the study,the union arrangement method of the Beidou base station and the IG material is introduced.In the field test,the actual application of the union monitoring method was investigated.In the partial-priority subgrade widening method,the prediction of subgrade deformation is also an important part.The research proposes a kind of sparse construction based on a multilayer feedforward neural network through L1 regular penalty and active set quadratic programming,called a lightweight neural network.The lightweight neural network driven by the sub-gradient quasi-Newton method is used to predict roadbed deformation.In the research,the calculation efficiency of the lightweight neural network and the optimal topology model under a simple structure are analyzed.Based on the analysis of the field test monitoring data,its predictive ability is analyzed.The result shows the practical value and popularization potential of the lightweight neural network in the prediction of the settlement of the widened subgrade in the Yellow River flood area in Shandong. |
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