Dynamic Response of Bridge-Landslide Parallel System under Earthquake

In order to further understand the instability mechanism and geohazard causation when the main sliding path of the slope body is parallel to the path of the bridge, the corresponding bridge-landslide parallel system is constructed for shaking table tests. This paper summarizes the combination forms of bridge-landslide model under different position and focused on the slope body located above the bridge deck. Firstly, based on the shaking table test results of El Centro (1940), the failure behavior of bridge-landslide parallel system was evaluated, and the changes of acceleration and deformation of bridge pile were subsequently analyzed. Then, the interaction bridge structure and sliding body were explained by the spectral features. The main conclusions are as follows. First, in the model test, the landslide belongs to the thrust-type landslide. Due to the barrier function of the bridge, the main failure site of landslide occurs in the middle and trailing edge of slope body. At the same time, the acceleration value of earthquake waves is 0.3 g, which is the key to this variation. Second, the acceleration response of the measuring points on the bridge pile and landslide increases with the increase of ground elevation. If the slope structure is damaged severely, the deformation response of weak interlayer is inconsistent with the surrounding soil structure. Third, with the increase of excitation power, the dominant frequency of bridge-landslide parallel system gradually transitions from low to high frequency rate, and the interaction of the parallel system weakens the influence of river direction on frequency. Finally, under the same working condition, the dynamic response of the measuring points has obvious regularity with the change of situation. But the response of the same points is not regular due to the different earthquake excitation intensity.

Formation Mechanism and Stability Analysis of the Hejia Landslide

The existing research data show that, after reservoir impoundment, due to the repeated rise and fall of water level and water-rock interaction, the mechanical parameters of landslide are reduced, which will have an adverse effect on the stability of landslide. Therefore, sufficient attention must be paid to the stability of slope after reservoir impoundment. Hejia landslide is the largest landslide near the bank of Miaojiaba hydropower station, and its stability plays an important role in the normal operation of the hydropower station. Through field investigation and analysis of regional geological conditions, it is concluded that Hejia landslide is a large-scale landslide, through long-term sliding-bending deformation; it is generated from the external hard rock with thick layers and sliding zone for layered soft rock; the formation mechanism of landslide is as follows: (1) high-steep and hard-soft layered slope is the slope structure condition that caused the large landslide; (2) the existence of thick soft rock belt provides material conditions for the formation of slip surface; (3) certain air conditions provide displacement space for the separation and disintegration of the sliding body, and the landslide is stable at present. Numerical analysis results show that reservoir impoundment will adversely affect the stability of landslide. In order to ensure the normal operation of power station, certain engineering measures must be taken to treat Hejia landslide. After taking measures, years of monitoring data show that the deformation of Hejia landslide tends to be stable, and the current operation is normal, indicating that the engineering treatment measures are reasonable and feasible.

Understanding rockfalls along the national road G318 in China: from source area identification to hazard probability simulation

Rockfall hazard is frequent along the national road (G318) in west Hubei, China. To understand the distribution and potential hazard probability, this study combines the result of a 3-years engineering geological investigation, statistical modeling, and kinemics-based method to identify risky road sections. Rockfall hazard probability is calculated by integrating spatial, temporal, size probability, and reaching probabilities of source areas. Rockfall source areas are preliminarily identified first by slope angle threshold (SAT) analysis. Random Forest model (RFM) and multivariate logistic regression model (MLRM) are then applied and compared to get the final susceptible source areas, considering eight factors, including slope, aspect, elevation, lithology, joint density, slope structure, land-use type, distance to the road. Temporal and size probability of source areas are separately obtained by Poisson distribution and power-law distribution theory. An important parameter (reach angle) for rockfall trajectory simulation was determined by back analysis in Flow-R and validated by field investigation. The results show good fitness with the measurements by field investigation. In the conditions of 5, 20, and 50 years return period, potential risky road sections are found out under two size scenarios (larger than 1 000 m3, 10 000 m3). This research helps the local government to completely understand the rock falls from source area existence and potential risk to roads.

Study on the hydrothermal coupling characteristics of polyurethane insulation boards slope protection structure incorporating phase change effect

The canals are essential for agricultural irrigation, shipping and industry as important hydraulic infrastructure. In the seasonal freeze regions, the water conveyance canals are damaged due to the effects of freeze–thaw cycles. The freeze depth of soil in the water transfer canal varies considerably due to changes in temperature and water content. This paper compared the relationship of freeze depth, temperature and water content by field tests and numerical calculation methods by incorporating phase change. The results from present study showed that the decrease in temperature causes the water in the soil to freeze, the ice front migrated downwards, and the water in soil below ice front gradually migrated towards the ice front resulting in a large difference in water content of the soil before and after freezing. The Polyurethane insulation board + Concrete board slope structure (PC) as an insulation slope structure was proposed in this paper to mitigate the effect of freezing and thawing on the water conveyance canals. The freeze depth decreased significantly under the protective effect. In addition, this paper compared the anti-frost effect of different thicknesses of polyurethane insulation boards, and the results provided a reference for the anti-frost design of water conveyance canals.

Investigation into a Homogenous Rock Slope Response Under Wide Frequency Seismic Loads Using a Large-Scale Shaking Table

The main objective of this study was to investigate the effect of input earthquake characteristics on the seismic response of a homogenous step-like rock slope. A sequence of shaking table tests was performed in a large-scale physical model with a size of 3.50 m, 0.68 m and 1.20 m in length, width and height, respectively. Results showed that the absolute peak ground acceleration motion amplification factor in horizontal direction (AAF-X) of upper part of the slope was amplified comparison with that at the slope toe while the absolute peak ground acceleration motion amplification factor (AAF-Z) acquired maximum value at the lower position of the slope. With the increasing of the excitation frequencies, the AAF-X around the slope crest increased firstly and then deceased, while the AAF-Z increased continuously. Seismic response of the slope showed strongest amplification when the normalized height of the slope H/λ (ratio of slope height to wavelength) was around 0.2 and AAF-X exhibited a decrease trend when H/λ was larger than 0.2. The AAF showed nonlinear tendency with the increases of the input amplitudes, especially near the shoulder of the slope. This phenomenon can be revealed by the relationship between the calculated resonance frequency or damping ratio of the slope and the amplitude of the input motion. The excitation amplitude has a “double-effect” on the seismic response of a step-like homogeneous rock slope. That is on the one hand, the larger the excitation amplitude, the stronger the acceleration intensity, the greater deterioration of rock slope structure or material and the larger damping ratio of the slope; on the other hand, more energy will be dissipated due to plastic deformation or particle friction of high damping ratio and weaker slope structure. These results could attribute to reveal the dynamic instability mechanism of the homogeneous slope.

Study on formation mechanism of granite eluvium landslide by field rainfall simulation

Granite residual soil is a kind of special soil, which is easy to induce geological disasters under the condition of heavy rainfall. Taking the mass landslides in Beiling area, Longchuan County, Guangdong Province as the background, the formation mechanism of typical landslides was explored by means of physical simulation, and the following conclusions were obtained: ① the influencing factors of landslides were rainfall intensity, physical and mechanical properties of rock and soil mass, slope structure; ② Rainfall does not cause the abnormal increase or decrease of soil pressure and pore water pressure in the slope, indicating that the failure of the slope is limited to the local failure of the slope surface and the slope toe, and there is no overall deformation and failure trend; ③ On the surface of the slope, the slope is eroded by rainfall, and on the foot of the slope, the free surface collapses and undergoes erosion. On the whole, the slope shows the characteristics of "step by step retreat and damage in turn"; ④ The evolutionary process of landslide can be divided into the following four stages: original slope evolution stage, soil particle migration stage, slope surface local failure stage and overall instability stage.

Performance Evaluation of Five GIS-Based Models for Landslide Susceptibility Prediction and Mapping: A Case Study of Kaiyang County, China

This study evaluated causative factors in landslide susceptibility assessments and compared the performance of five landslide susceptibility models based on the certainty factor (CF), logistic regression (LR), analytic hierarchy process (AHP), coupled CF–analytic hierarchy process (CF-AHP), and CF–logistic regression (CF-LR). Kaiyang County, China, has complex geological conditions and frequent landslide disasters. Based on field observations, nine influencing factors, namely, altitude, slope, topographic relief, aspect, engineering geological rock group, slope structure, distance to faults, distance to rivers, and normalized difference vegetation index, were extracted using the raster data model. The precision of the five models was tested using the distribution of disaster points for each grade and receiver operating characteristic curve. The results showed that the landslide frequency ratios accounted for more than 75% within the high and very high susceptibility zones according to the model prediction, and the AUC evaluating precision was 0.853, 0.712, 0.871, 0.873, and 0.895, respectively. The accuracy sequencing of the five models was CF-LR > CF-AHP > LR > CF > AHP, indicating that the CF-AHP and CF-LR models are better than the others. This study provides a reliable method for landslide susceptibility mapping at the county-level resolution.

Study on the Hydrothermal Coupling Characteristics of Polyurethane Insulation Boards Slope Protection Structure Incorporating Phase Change Effect

As an important hydraulic infrastructure, the canals are essential for agricultural irrigation, shipping and industry. In the seasonal freeze regions, the water conveyance canals are damaged due to the effects of freeze-thaw cycles. The freeze depth of soil in the water transfer canal varies considerably due to changes in temperature and water content. The paper compares the relationship of the freeze depth, temperature and water content by field tests and numerical calculation methods Incorporating phase change. The results show that the decrease in temperature causes the water in the soil to freeze, the ice front migrate downwards, and the water in soil below ice front gradually migrate towards the ice front, resulting a large difference in water content of the soil before and after freezing. An insulation slope structure, Polyurethane insulation board + Concrete board slope structure (PC), is proposed in this paper to mitigate the effect of freezing and thawing on the water conveyance canals. Under the protective effect, the freeze depth decreases significantly. In addition, this paper compares the anti-frost effect of different thicknesses polyurethane insulation boards, and the results can provide a reference for the anti-frost design of water conveyance canals.