The practice and theory of grouting engineering show that both injected medium porosity and grouting fluid weight play an important influence on the diffusion law and morphology of penetration grouting. However, the effects have not been well studied in the context of existing penetration grouting mechanisms. In this paper, the actual diffusion law and morphology of cement grout into the gravel soil are studied on the basis of indoor experiments, mathematical statistics, and theoretical analyses. Then, the three-dimensional space diffusion trajectory equation was quantitatively characterized. The influence of the coupling effect between gravel soil porosity and cement grout weight on diffusion morphologies of penetration grouting was discussed by the definition of the morphological deviation rate. Results show that actual penetration diffusion dimensions of cement grout into the gravel soil differ from that of theoretical values calculated by the penetration grouting mechanism, and its spatial diffusion morphology is approximated as ellipsoid. The coupling effect between gravel soil porosity and cement grout weight have a relatively significant effect on the diffusion morphologies of penetration grouting except for gravel soil with porosity <0.5 infiltrated by Newton-type and 0.5. The research results can provide theoretical support and technical references for the practical grouting engineering of gravel soil.

Niumiangou valley, the epicenter of the 12 May 2008 Wenchuan earthquake (MS 8.0), became an area with frequent and dense debris flow disasters post-earthquake. Based on the in situ investigations after the earthquake on 14 August 2010 and a series of gathered data, characteristics and dynamic analyses of post-earthquake debris flows in Niumiangou valley were conducted, and then their hazard degree was assessed. Some research conclusions are obtained: (1) these post-earthquake debris flows have some typical characteristics, such as rainstorm viscous-type debris flow, happening usually between 11 p.m. and 5 a.m., broken out in the main channel as well as six branch gullies at the same time and also induced in the branches with good vegetation; (2) the dynamic parameters of Niumiangou debris flow (including volumetric weight, velocity, peak discharge, impact force, total amount of debris flow, total amount of solid materials washed out by single debris flow, maximum height of the debris flow rises and super elevation in bend) are relatively significant, and due to which it can be indicated that these debris flow disasters have great destructive power and harmfulness; (3) the hazard degree of debris flow in Niumiangou valley is very high, compared with the debris flows that occurred in the years of 2008 and 2013 in Niumiangou valley post-Wenchuan earthquake, and the comparison result shows that the hazard degree of debris flow in Niumiangou valley is relatively higher, which is consistent with the current situation. Therefore, according to these results, debris flows in Niumiangou valley are in the development phase and large-scale rainfall-induced debris flow disasters, with greater damage and stronger wallop, will easily occur in the rainy seasons of the 20 years after the earthquake.

Major accidents occurred frequently in the road transportation industry, and the resulting harm to drivers, property loss, and traffic interruption are very serious. This study investigated 11 particularly major accidents involving commercial vehicles in China, and performed analysis on accident characteristics regarding the time, location, types of vehicles, and accident causation at different levels based on the 24Model. Large buses and dangerous goods vehicles were involved in 10 accidents and they all occurred on a freeway. The months from May to August, especially during the time periods of 2:00–4:00 and 14:00–16:00 every day, were the most prone to accidents. The driver’s speeding and fatigued driving, and vehicle failure were the direct causes of most of the accidents. The defects in organizational safety management involved 12 system elements, such as safety accountability, education and training, etc. Procedures are of no use if they were not followed, and there was often no effective process to assess the implementation of procedures in many organizations. The weaknesses in organizational safety culture were the source of accidents, which was mainly manifested in members’ inadequate cognition of key elements in the aspects of safety importance, safety commitment, safety management system, etc. Understanding the characteristics and root causes of accidents can help to prevent the recurrence of similar mistakes and strengthen preventative measures in road transportation enterprises.