Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test

Due to the lack of surface space, most structures are heading underground. The box culvert is underground infrastructure and serves to protect the buried structure from the underground environments, but it has a different characteristic from other structures in that the inner space is empty. Therefore, in this study, the vertical earth pressure which is the most significant effective stress acting on a box culvert was measured by conducting a geotechnical centrifuge model test. A box culvert was installed following the embankment installation method, and the vertical earth pressure acting on it was measured considering the cover depth, gravitational acceleration, and loading and unloading conditions. The soil pressure measured was greater than the existing theoretical value under high cover depth and the unloading condition, which is considered as the variability of many soils or the residual stress acting under the loading condition. Finally, a goodness-of-fit test was conducted as a part of variability analysis. The measured earth pressure was found to be considerably larger than the existing theoretical value, and the variability was large as well. This means the existing theoretical equation is under-designed, which should be reflected in future designs.

Prefailure Deformation of Nailed Deep Excavations under Surcharge by Centrifuge Model Test

To study prefailure deformations in nailed deep vertical excavations under various surcharges, four centrifuge tests were used to explain the lateral deformation of facing, the fracture mechanism of cement facing, and the settlement profile of the ground surface. The soil used in this research was Firoozkooh sand No. 161. Both surcharge applying and excavation were performed at 40 g acceleration. The depth of the excavation was 30 cm, the length of the nail varied from H/3 to 2H/3 (H: excavation depth), and the nails were installed horizontally. The nails were made of brass pipes and then sand coated. The results showed that the effect of surcharge on the lateral deformation of the facing as well as the fracture mechanism of facing is obvious. Also, it was seen that the ground settlement profile is two-line or three-line at the moment of facing fracture and is affected by surcharge.

Investigation on the Settlement of High Rockfill Embankment Using Centrifuge Tests

To study the deformation behavior of the high rockfill (HRF) embankment during construction and operation, based on more than a 50-m high rockfill embankment of the second-class road reconstruction project from Xunyang to Ankang of the national road 316 in Shaanxi, China, the centrifuge model test was performed to study the deformation laws of HRF embankment. The test results showed the following: (i) the HRF embankment was stable during construction and operation; (ii) during construction, the settlement occurred at the embankment top, and uplift occurred at the slope foot. Moreover, the deformation at the top was greater than that at the slope foot, and the deformations at both the top and the slope toe reached the maximum value at the end of construction; (iii) during operation, the settlement at the embankment top continued, and it changed rapidly at the start of operation. And then, the rate of the settlement slowed down and reached a steady state finally. The deformation of the slope foot was very small. This study can provide basis and reference for the design and construction of a similar project in mountain areas.

Centrifuge Model Test and Numerical Analysis on Failure Behavior of a Loess – Paleosol Landslide Caused by Excavation

Many landslides are induced by excavation activities in the loess region. In this article, a loess – paleosol slope model was built and tested under 80 g centrifugal environment. Three certain angle excavations were simulated by manipulator movement. The mini pressure sensor and PIV system were utilized to monitor experimental process respectively. It can be found that the slope from excavation to failure, is liable to form the deep and shallow two sliding surfaces. The distance perpendicular to slope surface was measured as 9.6 cm for the deeper sliding surface, and 4.2 cm for the shallower one. Both of sliding surfaces are caused by the interaction of tensile failure and shear failure, specifically presented as the tensile failure concentrating on the upper part and the shear failure on the lower part. The loess slope can be split into three zones by response of excavation unloading (i.e., the sliding zone, the influenced zone and the uninfluenced zone). The failure pattern belongs to a retrogressive type with the bulging front edge and tension cracking trailing edge. The causes of the fractures on the slope top can be divided into different sections. The fracture near the slope top is induced by tension and shear force. But the fracture away from slope top is only induced by tension. In addition, the plastic zone development distribution of simulation has a good consistency with the centrifugal model deformation zoning diagram. These results can provide guidance for excavation activities in loess – paleosol slopes.

An Investigation of Effects and Safety of Pipelines due to Twin Tunneling

To efficiently and accurately predict the effects of twin tunneling on adjacent buried pipelines, the effects of upward and downward relative pipeline-soil interactions were considered. A series of numerical parametric studies encompassing 8640 conditions were performed to investigate the responses of a pipeline to twin tunneling. Based on the dimensionless analysis and normalized calculation results, the concept of equivalent relative pipeline-soil stiffness was proposed. Additionally, expressions for the relative pipeline-soil stiffness and relative pipeline curvature and for the relative pipeline-soil stiffness and relative pipeline settlement were established, along with the related calculation plots. Relying on a comparison of prediction results, centrifuge model test results, and field measured results, the accuracy and reliability of the obtained expressions for predicting the bending strain and settlement of adjacent buried pipelines caused by twin tunneling were validated. Based on the calculation method, the maximum bending strain and maximum settlement of pipelines can be calculated precisely when the pipeline parameters, burial depth, soil parameters, and curve parameters of ground settlement due to tunneling are provided. The proposed expressions can be used not only to predict the maximum bending strain and maximum settlement of pipelines caused by single and twin tunneling but also to evaluate the effects of single and twin tunneling on the safety of existing buried pipelines. The relevant conclusions of this article can also provide a theoretical basis for the normal service of buried pipelines adjacent to subway tunnels.

Centrifuge Model Test on the Settlement of Valley-Type Loess Filled after Construction and Subjected to Rainfall Infiltration

With the rapid development of infrastructure construction in western China where hilly and gully areas are distributed, there are lots of large-scale filling engineering in recent years. In the area where collapsible loess is widely distributed, it is inevitable to use loess as filling material. Considering the collapsibility of loess, centrifuge model tests were conducted to study the settlement of loess fill in a valley after construction and subjected to rainfall infiltration. To provide a comparison, a centrifuge model test of loess filling body on a flat ground was conducted, and results showed that the settlement of loess fill during the construction stage is larger than the one at the postconstruction stage, and the unloading rebound deformation caused by decreasing gravity is about 15% of the deformation induced by increasing gravity. Two centrifuge model tests were conducted to study the settlement of the loess filling body in a valley; the varying characteristics of settlement and earth pressure with time at the postconstruction stage and subjected to rainfall infiltration were investigated. Differential settlement in the ground surface was observed at the postconstruction stage, and it was found to become very small under the rainfall infiltration condition. Comparison of the test results showed that insufficient compaction in the lower part of the filling body significantly increases the ground settlement at the postconstruction stage.