Computed tomography (CT) technology is a kind of nondestructive image reconstruction technology. CT visualization technology is introduced into the physical model test of a single pile, which can visualize a rock-socketed pile in soft rock under different pile top loads. In this article, the visualization process of a model test of a rock-socketed pile in soft rock is carried out by medical CT. The implementation procedure, the composition of the device, and the technical requirements of the test equipment, as well as the CT scanning operation of nondestructive visualization technique of the single pile model test, are introduced in detail. The influence of a marked layer setting, side wall effect, size of the model cylinder, and model pile on the visualization effect of a single pile model test is discussed. The feasibility and reliability of the model test visualization technology of a rock-socketed pile in soft rock are demonstrated by examples, and the failure mode of rock-socketed pile in soft rock is intuitively revealed to be the spherical cavity expansion mode of the pile end.

The soft rock was simulated by cement, plaster, sand, water, and concrete hardening accelerator in this paper. Meanwhile, uniaxial compressive strength tests and triaxial compression tests were conducted to study the mechanical properties of simulated soft rock samples. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted by using a device which combined test apparatus with a GCTS dynamic triaxial system. Test results show that the optimal mix ratio is cement : plaster : medium sand : water : concrete hardening accelerator = 4.5% : 5.0% : 84.71% : 4.75% : 1.04%. The static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation and cyclic secant modulus of the pile head. The accumulated deformation increases with increasing numbers of cycles. However, the cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles and finally remains stable after 50 cycles. According to the test results, the development of accumulated settlement was analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio, and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to traffic loading.

Purpose: This paper aims to propose a shape factor for granular materials based on particle shape. The scientific goal is to investigate the influence of particle shape on the mechanical properties of rockfill materials.Design/methodology/approach: The method of generating four regular-shaped particles is based on the observation that most rockfill grains are regarded as like-triangle, like-rhombus, like-square and like-hexagon. A shape factorFthat is developed using the Blaschke coefficient and a concave–convex degree is proposed. A biaxial compression test on rockfill materials under stress path is numerically simulated by discrete element method. The evolution of the shape factorFunder the simulated stress paths is analyzed, and particle breakage rate, peak intensity and peak-related internal friction angle for rockfill materials are derived. A method of determining the shape factorFinvolved in the two functions is proposed.Findings: A new micro-parameter is calibrated using the test data of one rockfill material. Particle shape greatly affects the particle breakage rate, peak intensity and peak-related internal friction angle for rockfill materials. The final experimental grading curves all approach the particle breakage grading curve proposed by Einav (the fractal dimension is 2.7).Originality/value: This study proposes a shape factorF, which describes the geometric features of natural rockfill particles. The proposed shape factorFhas a simple structure, and its parameters are easy to determine. The method provides an opportunity for a quantitative study on the particle shape of granular materials, and this study helps to better understand the influence of particle shape on the mechanical characteristics of rockfill materials.

A landslide susceptibility map plays an essential role in urban and rural planning. The main purpose of this study is to establish a variable-weighted linear combination model (VWLC) and assess its potential for landslide susceptibility mapping. Firstly, different objective methods are employed for data processing rather than the frequently-used subjective judgments: K-means clustering is used for classification; binarization is introduced to determine buffer length thresholds for locational elements (road, river, and fault); landslide area density is adopted as the contribution index; and a correlation analysis is conducted for suitable factor selection. Secondly, considering the dimension changes of the preference matrix varying with the different locations of the mapping cells, the variable weights of each optimal factor are determined based on the improved analytic hierarchy process (AHP). On this basis, the VWLC model is established and applied to regional landslide susceptibility mapping for the Shennongjia Forestry District, China, where shallow landslides frequently occur. The obtained map is then compared with a map using the traditional WLC, and the results of the comparison show that VWLC is more reasonable, with a higher accuracy, and can be used anywhere that has the same or similar geological and topographical conditions.

Using the model test technology of the rock-socketed pile in soft rock in consideration of the influence of the overburden, the physical model test with different overburden pressure and different rock-socketed depth is carried out. The vertical bearing mechanism and law of the rock-socketed pile in soft rock are analysed through the results of axial force distribution, shaft resistance distribution, load sharing ratio of shaft resistance and base resistance, shaft resistance relationship between shaft resistance and displacement, and relationship between base resistance and displacement, etc. Based on the accurate qualitative analysis of indoor model test results, and combined with the measured data and engineering experience at home and abroad, the vertical bearing characteristics of the rock-socketed pile in soft rock are comprehensively interpreted, and the vertical bearing mechanism and its influencing factors of the rock-socketed pile in soft rock are revealed.

The main purpose of this study was to establish a data-driven approach and assess its potential for shallow landslide susceptibility mapping of the Shennongjia Forestry District, China. For the data processing, Fisher segmenting was used for the classification of topographical factors (gradient, relief amplitude, plan curvature, and normalized difference vegetation index) and the improved Otsu method was used to determine the buffer length thresholds of the locational factors (proximity to roads, rivers and faults). The computations show that these two objective methods help to avoid the uncertainty caused by the subjective judgments and the obtained thresholds are more consistent with actual conditions. Considering the different data types, the locational and topographical factors were evaluated by fuzzy comprehensive evaluation while the geological factors were evaluated by frequency index, and then the three separate evaluations were combined using radar chart analysis. The validation result shows that the susceptibility map based on a data-driven approach has a high accuracy of prediction and this approach will be salutary for risk mitigation and land-use management in mountainous regions.