Buried steel gas pipelines are increasingly facing safety challenges due to the escalating traffic loads and varying burial depths, which could potentially lead to hazards such as leakage, fire, and explosion. This paper investigates stress mechanisms in buried steel gas pipelines subjected to vehicular loading through integrated analytical approaches. Theoretical modeling incorporates three key components: dynamic vehicle load characteristics, soil-pipeline interaction pressures, and stress distribution angles across pipeline cross-sections. Stress variations are systematically quantified under varying soil conditions and load configurations. A finite-element model was developed to simulate pipeline responses, with computational results cross-validated against theoretical predictions to establish stress profiles under multiple operational scenarios. Additionally, this paper employ fatigue accumulation damage and reliability theories, utilizing Fe-Safe software to evaluate pipeline reliability, determining fatigue life and strength coefficients for various loads and burial depths. Based on these analyses, this paper develop risk control measures and protective methods for buried steel gas pipelines, validated through finite-element and fatigue analyses. Overall, this paper offers insights for preventing and controlling risks to buried steel gas pipelines under vehicle loads.

Due to the unobservable nature of underground construction and the destructive nature of horizontal directional drilling rigs with high power, this type of construction has become one of the most important causes of failure of long-distance natural gas pipelines. In recent years, horizontal directional drilling construction has caused pipeline accidents frequently. Once the accident occurs, the normal operation of natural gas pipelines cannot be ensured. Therefore, studying the damage mechanism of buried natural gas pipelines under horizontal directional drilling loads is important for the safe operation of pipelines. This paper combines the construction characteristics of horizontal directional drilling and the actual situation of natural gas pipelines to explore the relationship between horizontal directional drilling and pipelines. The force situation of pipelines after contacting directional drilling bits is analyzed by the drill bit-soil-pipe finite element model created in the ABAQUS software. The Johnson-Cook ductile damage model was utilized to determine the pipe's damage condition. The sensitivity analysis results show that he order of the impact of key parameters on the dynamic response of the pipe is bit thrust > wall thickness > bit diameter > pipe diameter > bit speed > number of bit teeth > pipe operating pressure. Therefore, priority should be given to controlling the size of the drilling thrust and the speed of the drill bit to reduce the damage to pipelines by horizontal directional drilling construction. In addition, appropriately reducing the pipeline operating pressure can also reduce the risk of the pipeline being damaged by horizontal directional drilling construction.

Dealing with collapsible soils consistently presents a crucial challenge for geological and geotechnical engineers. Loess soil is among the most widely recognized types of collapsible soils, covering approximately 10 % of the Earth's land surface. Loessic soil is a sedimentary deposit primarily composed of silt-size grains, loosely bound together by calcium carbonate. In Iran, approximately 17 % of Golestan province is covered by silty, clayey, and sandy loesses, primarily composed of loessic soil. Additionally, several energy transmission lines in this province traverse these loess-covered areas. Based on the reports from Golestan Gas Company experts, the scouring of gas pipeline channels in various regions, such as Dashli-Alum in Maraveh-Tappeh city, causes significant risks in the traffic roads and is one of the most critical issues facing this company. This research assessed the dispersion and collapse potentials of loess soil using a range of field exploration and laboratory testing methods. These methods included atomic absorption spectroscopy, the double hydrometer, scanning electron microscope photography, wavelength-dispersive X-ray fluorescence spectrometry, and consolidation tests. The results indicate that soil collapsibility was acquired as one of the components of the scouring phenomenon occurrences. To achieve an optimal solution, the effectiveness of the chemical stabilization method involving cement, bentonite, micro- silica, and synthesized nano-titanium additives was evaluated through an oedometer, Atterberg limits, uniaxial compression, and direct shear tests. Additives dry mixing of cement and nano-titanium were obtained as the optimal stabilization solutions against scouring compared to other additives. However, considering the environmental impacts of cement production and use, nano-titanium presents a more environmentally sustainable option due to CO2 absorption and reduced damage potential to vegetation.