Field Experiment on Soaking Characteristics of Collapsible Loess

Collapsible loess tunnel foundation reinforcement is a new challenge in the construction process of tunnel engineering. According to the field displacement and stress monitoring of the Fujiayao loess tunnel, this paper investigates the reinforcing effect of a high-pressure jet grouting pile on a collapsible loess tunnel foundation in the deep large-span tunnel. The field monitoring method was employed to address the performance of tunnel foundation settlement, additional stress, earth pressure, rock pressure, etc. The results indicate that the stress on the pile tops and the earth pressure between piles increase gradually over time in two stages: stress increases rapidly in the first 45 days and, after this period, stress tends to gradually stabilize. Further, stress increases uniformly with the distance from the centerline of the tunnel, and the rock pressure of the tunnel sidewalls tends to be stable within two months of being constructed. Additional stress on the tunnel foundation increases linearly with time, and it is uniformly distributed in the vertical and horizontal directions of the tunnel section. Settlement of the tunnel foundation also gradually increases with time, and it tends to be stable at 50 days from the time of construction. Additionally, the settlements of different monitoring points are similar at the same depth. The research results will further improve the theoretical knowledge of tunnel bottom reinforcement in the loess tunnel, which not only can effectively guide the design and construction of the loess tunnel and reduce disease treatment cost but also can provide the necessary basic research data and scientific theoretical basis for revision of the corresponding specifications of highway tunnels and railway tunnels.

Section: Introductionmentioning

confidence: 99%

Displacement and Stress Characteristics of Tunnel Foundation in Collapsible Loess Ground Reinforced by Jet Grouting Columns

Liu

et al. 2018

“…erefore, the uniform pressure applied on the surface of the soil, as illustrated in Figure 4(b), is not caused by the superstructure. e application of uniform pressure is equivalent to the effect of water on loess to some extent to force the occurrence of displacement, which can be used to analyze the equivalent amount of collapsible deformation [4,5]. e schematic diagram of the two methods is illustrated in Figure 4, and the input calculation parameters are displayed in Table 3.…”

Section: Comparison Of Modulus Reduction Methods and Force-water Equivalent Methodsmentioning

confidence: 99%

“…For instance, the in situ test and field wetting test can directly measure the deformation amount and estimate the deformation characteristics of collapsible loess, and the obtained test data are accurate and reliable. Scholars [1][2][3][4][5] have implemented a significant number of field wetting tests in different areas to collect valuable measured data. e field wetting test conducted in Pucheng Power Plant in Shaanxi Province, China, is one of the representatives [2].…”

Section: Introductionmentioning

confidence: 99%

A Simplified Approach to Estimating the Collapsible Behavior of Loess

Hua

Deng

Zhang

et al. 2020

Due to the particularity and complexity of loess, it is challenging to estimate its collapsible behavior numerically at present. This paper aims to propose a simplified approach, which is named as the modulus reduction method, to estimate the collapsible behavior of loess. For loess upon wetting, the modulus reduction method assumes that loess collapses as a result of strength reduction due to the additional stress induced by increasing bulk density. Thus, special attention is given to the confirmation and determination approaches of bulk density and deformation modulus of loess upon wetting. Subsequently, a comparative numerical analysis based on the modulus reduction method and the force-water equivalent method, which is commonly used for the analysis of negative skin friction on piles in collapsible soil, is investigated. It turns out that the result obtained by the modulus reduction method is more consistent with the collapse mechanism of loess compared with that derived by the force-water equivalent method. Finally, a case history concerning a published field test of loess upon wetting is studied, and the result shows that the simulated deformation characteristics by adopting the modulus reduction method agree excellently well with the measured data. The case study validates that the modulus reduction method is feasible to analyze the collapse of loess and suitable for the numerical simulation involving collapsible loess.

“…e results of model tests showed that the volumetric moisture content of the slope region where the localized failure initiated was noted reaches a nearly saturated value. Wang et al [21] investigated the soil-atmosphere interaction for foundation by numerical analysis using data from Nairobi. It was further noted that the migration of moisture and the vertical movement within the foundation are obviously affected by rainfall and evapotranspiration.…”

Section: Introductionmentioning

confidence: 99%

Moisture Migration and Control of New Embankment for Reconstruction and Expansion Project in Southern China

Zhang

Zeng

et al. 2020

In hot and humid regions of southern China, the volumetric moisture content of the embankment after opening to traffic for a period of time reaches a stable state, and it is higher than the design value. When it was widened, the humidity gradient and exchange were formed due to the difference in moisture content between the existing and new embankment. To reveal the moisture migration of the existing and new embankment and control the rise of volumetric moisture content in new embankment, six frequency domain reflectometry sensors were installed in existing and new embankment to monitor the volumetric moisture content. A finite element model for the embankment was established and verified with the measured data. And seven numerical analyses of transient seepage in the new embankment of the cushion, cover, and partition using capillary barrier by sand were simulated. The results show that the volumetric moisture contents of the new embankment in southern China gradually increase and eventually reach an equilibrium state. The increase in water comes from the slope, the foundation, and the existing embankment. Early in the first 1∼2 years, the water mainly comes from the foundation and the existing embankment. After that, as time goes by, the water comes mostly from the slope infiltration and gradually migrates to the foundation and the existing embankment. Finally, the volumetric moisture content and the water storage gradually reach equilibrium. The volumetric moisture content of the new embankment using capillary barrier by sand at the cushion, the cover, and the partition is maintained as the construction volumetric moisture content. This combination is a very effective method to control the humidity stability of the new embankment in southern China.