Abstract
In the Northwestern part of Loess Plateau of China, the ravine and valley are numerous; therefore, high-filled cut-and-cover tunnels (HFCCTs) play a major role in meeting traffic needs and creating a great deal of usable land. However, due to higher backfill soil, a high earth pressure is generated, which affects the safety of HFCCTs. To this end, using the discrete element method (DEM), three load reduction measures were introduced to evaluate HFCCT: the cross section types of HFCCT; the combination of optimized cross section type with load reduction using expanded polystyrene (EPS); and the combination of optimized cross section type with load reduction using the EPS and concrete wedge (CW). We evaluated changes in earth pressure of HFCCTs with reference to the density and laying position of EPS and the height as well as width of CW. Parametric DEM studies were performed to characterize these influential factors. It was found that different cross section types of HFCCT have a certain influence on earth pressure distribution, and load reduction effects of EPS were extremely obvious, resulting in a sharp drop in vertical earth pressure on top of HFCCT and a slight growth in lateral earth pressure on the sides of HFCCT. Moreover, installation of CWs reduced the VEP and LEP of HFCCT. These factors were also shown to exert important effects on load reduction mechanisms of HFCCT. Based on their influence on earth pressure of HFCCT from a macroscopic and microscopic view, optimal values for influential factors were derived.
Highlights
To overcome the challenges associated with mountains and less land in transportation network construction in the Loess Plateau of northwest China, a large number of high-filled cut-and-cover tunnels (HFCCTs) are applied
Conclusions e PFC2D software was used to assess the influence of different cross section types and load reduction material characteristics on earth pressure distribution around HFCCT. e optimal values of effects under three load reduction measures were obtained
Several conclusions can be drawn from this study: (1) Earth pressure distribution was optimized by changing the cross section optimization coefficient of HFCCT
Summary
To overcome the challenges associated with mountains and less land in transportation network construction in the Loess Plateau of northwest China, a large number of high-filled cut-and-cover tunnels (HFCCTs) are applied. It is important to evaluate the impact of different cross section types and characteristics of load reduction materials on earth pressure distribution around HFCCT. E above studies found that the cross section type of high-filled structure has a certain influence on earth pressure distribution around it. Combined effects of optimal cross section type and load reduction material characteristics (density and laying position of EPS; width and height of concrete wedges (CW)) were studied. E effects of different cross section types and characteristics of load reduction materials on earth pressure distribution above HFCCT were analyzed using the PFC2D software. Vertical displacement (VD), and microcontact of soil particles were evaluated by changing different influencing factors (cross section types, density and laying positions of EPS, as well as CW height and width). Numbers 10 to 18 measurement circles were used to measure VD of soil particles above the HFCCT and the VEP of backfill soil between the two concrete wedges; measurement circles numbered 14 and 12 (or 14 and 16) were used to calculate relative vertical displacements (RVD) of soil particles above the HFCCT; measurement circles numbered 5, 14, and 23 to 28 were used to measure VEP at different backfill depths above HFCCT; and measurement circles numbered 19 to 22 were used to measure VEP above the CWs, while those numbered a to j (or a’ to j ’) were used to measure LEP on both sides of HFCCT
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