In-Site Monitor During Road Reconstruction In Mountain Areas

Two typical problems encountered in highway reconstruction in mountain areas are stability of reinforced steep slope and non-uniform settlements between old subgrade and new subgrade. These are the cases during the reconstruction of Er-kang section of state highway G318.By means of field monitor, these two problems are investigated and analyzed, Attentions are paid to following aspects in the research.1. In slope stability monitor, deformation is the main factor to be monitored while the stress measurement is the supplement. Based on geotechnical data and slope reinforcement design, numerical analyses are performed. Farther on, a monitoring system is worked out. Similarly, a system is designed for monitoring subgrade settlement on the basis of numerical simulation. Influence of the retaining wall on the settlement is emphasized during the system design. Moreover, problems such as data collection and the use of measuring instruments, data process, etc, are presented. This helps to accumulate experience on field monitor of the similar engineering project.2. Slope deformation monitor consists of surface displacement measurement and inner deformation measurement using inclinometers. Collected data of surface displacement fluctuates from time to time, indicating that the slope is generally in a stable condition. Due to the influence of many factors, such as the limitation of measuring instrument, unpredictable environment conditions, however, the degree of accuracy of the surface displacement measurement is not very high. On the contrary, data collected from inclinometers are generally reliable with the accuracy being as high as 0.01mm. Besides, inner deformation measurement is relatively undisturbed during the course of construction. Therefore, it is proper for this project to monitor slope deformation byinclinometers, while the surface displacement survey can be used as a supplement.3. According to the data obtained in the field, reinforcement particularly the application of the prestressed cables, prevented farther denfavorable deformation of the slope. Meanwhile, data about the variation of the prestress within the cables confirm that function of the reinforcement can be very complex. It involves a slow process of adjustment between rock mass and prestressed cables until a state of compatibility between them is reached.4. Data obtained from in situ survey laid the foundation for optimization of the engineering design. Obtained data showed that the slope is generally in a stable state during the slope cut and slide on a large scale is unlikely. For this reason, reinforcement on the lower part of the slope can be reduced by replacing long anchor rods with the short ones.5. Obtained data showed that subgrade settlement near the retaining wall is larger than that far away from the wall. Difference of subgrade settlement was believed to be the results of displacement of the retaining wall as well as that of soil consolidation. It was hence suggested that pavement construction should be postponed until both the retaining wall and the settlement were stabilized.6. Data showed that both displacement of the retaining wall and the subgrade settlement experienced a slow process from accelerated change to the states of stabilization. It was' deduced that relaxation of retaining wall's constraint due to the displacement resulted in the increase of soil settlement near the wall. In this sense, stability of the retaining wall is one of the Key factors affecting non-uniform settlement of the subgrade.