The comprehensive evaluation of pipeline loess collapsibility risk is a necessary means to control the safety risks of pipelines in the collapsible loess section. It is also one of the critical scientific bases for risk prevention, control, and management. The comprehensive evaluation system of cloud theory consists of quantitative and qualitative indexes, and the evaluation system has the characteristics of randomness and fuzziness. In view of this problem, the standard qualitative and semi-quantitative evaluation methods have intense subjectivity in dealing with the uncertainty problems such as randomness and fuzziness of the system, the cloud theory, which can effectively reflect the randomness and fuzziness of things at the same time, is introduced. The state scale cloud and index importance weight cloud of pipeline loess collapse risk are constructed by the golden section method. The uncertainty cloud reasoning process of the quantitative indexes and the expert scoring method of the qualitative indexes are proposed. The comprehensive evaluation model of loess collapsibility risk of oil and gas pipeline is established, and the engineering example is analyzed. The complete evaluation results of 10 samples to be evaluated are consistent with the results of the semi-quantitative method and are compatible with the actual situation. The evaluation process softens the subjective division of index boundary, simplifies the preprocessing of index data, realizes the organic integration of quantitative and qualitative decisions, and improves the accuracy, rationality, and visualization of the results.
Ground collapse is one of the main geological disasters affecting the safe operation of oil and gas pipelines. Studying the stress-strain characteristics of pipe-soil interaction under ground collapse has an important guiding role for the prevention of ground collapse and the safety protection of pipelines. The current results are mostly concentrated in a single theory or the stress of the pipeline itself, which cannot fully consider the pipe-soil interaction. In this paper, ABAQUS is used to establish the finite element geometric model. Considering the pipeline and the surrounding geological environment conditions, the study is carried out from five aspects: the length of the collapse area, the thickness of the cover layer, the buried depth of the pipeline, the diameter of the pipeline, and the thickness of the pipeline. The displacement of the pipeline soil, the deformation of the pipeline, and the characteristics of the pipeline stress are analyzed, and the variation law is determined through the development trend of the pipeline stress and strain. At the same time, by fitting and analyzing the relationship between the span of different subsidence areas, the thickness of the cover layer, the buried depth of the pipeline, the diameter of the pipeline, the thickness of the pipeline, and the maximum deformation of the pipeline, the reference value of the maximum subsidence displacement of the pipeline under the action of ground collapse is proposed. The work has practical application value for pipeline monitoring, early warning, and disaster management.
The distribution of pipeline water damage hazards and the control effect of the disaster-inducing environment are the theoretical basis of risk assessment and prevention decision-making. Based on the observation data of pipeline water damage hazard at the northern foot of Yumu mountain from 2015 to 2021, indexes of the point density and linear density were introduced to analyze the spatial and temporal distribution law of water damage hazard, and the control effect of disaster inducing environment factors was discussed, such as rainfall, slope, pluvial fan superimposition, and scarp. The results show that: in terms of time, the point density and linear density of water damage hazard show a downward trend along with the pipeline operation, and the decrease of density of river channel is higher than that of slope water damage hazard, but the local steep rise phenomenon is significant. In terms of space, the point density of water damage hazard is affected by both the slope water damage hazard and the river channel water damage hazard, the influence width of the former is greater than that of the latter, so the linear density of water damage hazard is controlled by the slope water damage hazard. The frequency and intensity of heavy rain have a significant impact on the density of water damage hazards, especially on the slope water damage hazard. The longitudinal slope of Piedmont is positively correlated with the linear density of water damage hazard. Water damage hazard is developed in the superimposition range of pluvial fan, and its impact on linear density is more significant than that on point density. Its impact on slope water damage hazard is more significant than that on river channel water damage hazard. The point density of the water damage hazard is negatively correlated with the distance between the pipeline and the scarp, and the linear density of the water damage hazard is positively correlated with the distance between the pipeline and the scarp. The crossing and accompanying of the pipeline and the scarp is the main control factor for the alternate development of the slope water damage hazard and the river channel water damage hazard.
The washout by slope flow along long-distance oil & gas pipelines is a common geological hazard that occurs when pipelines pass through the alluvial-proluvial fan section of mountain piedmont. Accurate and effective evaluation of the risk of single washout by slope flow is an important basis for disaster prevention and control decisions. According to the characteristics of the lack of basic research data in the development area of washout by slope flow, the complexity of the risk assessment structure and the strong randomness and ambiguity of the multi-index system, on the basis of rapid acquisition of initial data of indicators through field survey, simple experiment and sampling analysis, a quantitative index cloud reasoning risk evaluation model for slope flow washout of pipeline was established by introducing single-condition and single-rule cloud reasoning with summation integration weighting algorithm, and carry out instance verification. The evaluation results of 11 samples showed medium and relatively high risks, and the overall distribution trend is relatively concentrated. Compared with the results obtained by the entropy weight-extension method and the standard recommendation method, the proposed method is more in line with the small-scale disaster background analysis and the reality of the study area, and it’s also more beneficial to ensure the safe operation of pipelines. In this method, the obtainment of the source data is reliable, objective, and the preprocessing is simplified, the index weighting and classification are more reasonable, and the evaluation process takes into consideration of both the randomness and ambiguity of the system, which improves the accuracy and effectiveness of the evaluation results. It also provides a new way of thinking to other related research.
The comprehensive evaluation of pipeline loess collapsibility risk is a necessary means to grasp the safety risks of pipelines in the collapsible loess section, and it is also one of the key scientific basis for risk prevention, control and management. The comprehensive evaluation system of cloud theory consists of quantitative and qualitative indexes, and the evaluation system has the characteristics of randomness and fuzziness. Aiming at the problem that the common qualitative and semi-quantitative evaluation methods have strong subjectivity in dealing with the uncertainty problems such as randomness and fuzziness of the system, the cloud theory, which can effectively reflect the randomness and fuzziness of things at the same time, is introduced, and the state scale cloud and index importance weight cloud of pipeline loess collapse risk are constructed by golden section method. The uncertainty cloud reasoning process of the quantitative indexes and the expert scoring method of the qualitative indexes are proposed. The comprehensive evaluation model of loess collapsibility risk of oil and gas pipeline is established and the engineering example is analysed. The comprehensive evaluation results of 10 samples to be evaluated are basically consistent with the results of semi-quantitative method, and are consistent with the actual situation. The evaluation process softens the hard division of index boundary, simplifies the index data pre-processing, realizes the organic integration of quantitative and qualitative, integrated decision-making, and improves the accuracy, rationality and visualization of the results.
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