Research on the Combined Load-Bearing Mechanism of Deeply Buried Pressure Pipelines Under High Internal Water Pressure
ObjectiveAccurately calculated the stress and deformation fields of deep-buried pressure pipelines subjected to high internal water pressure, with a specific focus on the influence of fractures in the concrete layer. The mechanisms of load transfer and distribution within the pipeline's bearing...
Saved in:
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2025-01-01
|
| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202500321 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | ObjectiveAccurately calculated the stress and deformation fields of deep-buried pressure pipelines subjected to high internal water pressure, with a specific focus on the influence of fractures in the concrete layer. The mechanisms of load transfer and distribution within the pipeline's bearing system were elucidated, considering various influencing factors such as internal water pressure levels, interlayer gap between structural components, and the geological categories of the surrounding rock.MethodsThe bearing behavior of pressure pipes was simplified as a plane strain problem, and the stress and deformation fields were solved using the power series method of complex function theory. The core of this approach lied in determining the potential functions for the steel lining and surrounding rock layers, as well as the contact stresses between each structural layer. 1) Considering the presence of interlayer gap, the bearing process is divided into two stages: the free bearing stage and the joint bearing stage. During the free bearing stage, only the steel lining underwent radial expansion under internal water pressure until its outer boundary comes into contact with the inner boundary of the concrete layer. In this stage, the corresponding internal water pressure and form of the steel lining’s potential function can be determined based on the prescribed deformation value at the outer boundary of the steel lining. 2) In the joint bearing stage, when the internal water pressure exceeded a critical threshold, the steel lining and concrete layer achieved full contact and continued to expand together. At this point, the concrete layer and surrounding rock acted as an external constraint system, jointly supporting a portion of the internal water pressure. 3) Under high internal water pressure, the concrete layer experienced significant circumferential tensile stress, leading inevitably to the formation of radial cracks and the loss of its circumferential load-bearing capacity. In this case, the concrete layer can only transmit radial loads and was therefore modeled as an equivalent spring layer with a defined stiffness coefficient. 4) Based on the deformation compatibility conditions among the steel lining, concrete layer, and surrounding rock during the joint bearing stage, the contact stresses and forms of the potential functions between the structural layers can be determined. 5) Utilizing the superposition principle of elasticity theory, the final stress distribution and deformation characteristics of the pressure pipe structure can be obtained, enabling the calculation of the surrounding rock’s load-sharing ratio.Results and DiscussionsThis study investigated the influence of internal water pressure, gap size between structural layers, and surrounding rock classification on the joint load-bearing behavior of pressure pipelines. Comparative analyses were conducted with and without consideration of concrete cracking effects. The key findings are summarized as follows:1) Internal water pressure induced radial expansion of the pressure pipeline, with its effects-manifested as stress increments and deformations-diminishing progressively outward from the inner boundary. When the interlayer gap was small, the external concrete layer and surrounding rock can bear a significant portion of the internal water pressure. Therefore, in engineering design, if the surrounding rock was structurally sound, stable, and the quality of concrete filling can be assured, the thickness of the steel lining may be appropriately reduced to optimize construction costs. 2) When cracks developed in the concrete layer, leading to the loss of its circumferential load-bearing capacity, the corresponding internal water pressure was redistributed between the steel lining and surrounding rock according to their respective stiffness characteristics. This resulted in increased radial stress, deformation, and circumferential stress in both components. Due to its high stiffness and direct exposure to internal water pressure, the steel lining assumed a larger share of the load, while the contribution of the surrounding rock decreases. The extent of this shift depended on the overall structural parameters and the magnitude of the applied internal water pressure. (3) Given that the deformation of the steel lining under internal water pressure typically occurred at the millimeter scale, even minor interlayer gaps significantly affected the load transfer and distribution within the composite system formed by the steel lining, concrete layer, and surrounding rock. For instance, based on the parameters used in this study, the surrounding rock’s load-sharing ratio decreased from 71.31% under zero-gap conditions (<italic>t</italic>=0 mm) to 44.35% when the gap reached 1 mm. (4) The classification of surrounding rock had a substantial impact on the load-sharing ratio of the surrounding rock. Without considering concrete cracking, the difference in circumferential tensile stress in the steel lining between Class II and Class V surrounding rock conditions reached 40.93MPa, with a corresponding difference of 20.56% in the surrounding rock’s load-sharing ratio. When concrete cracking was considered, these differences became more pronounced: the maximum difference in circumferential stress increased to 118.03MPa, radial deformation differed by up to 1.6mm, and the surrounding rock load-sharing ratio varied by as much as 59.31%. These findings indicated that the Class V surrounding rock contributed very little to internal water pressure resistance under such conditions, implying that the steel lining became the primary load-bearing component. To enhance the surrounding rock’s contribution, reinforcement measures such as grouting may be necessary.ConclusionsAiming at the calculation problem of load transfer and distribution in deep-buried pressure pipelines under high internal water pressure conditions, a power series solution method based on complex variable functions was proposed. By solving the potential functions for the steel liner and surrounding rock as well as the contact stress between the bearing bodies, the stress, deformation at any position of the bearing structure and surrounding rock sharing rate can be accurately determined. This method accounted for the loss of circumferential bearing capacity due to concrete layer cracking by modeling it as a spring layer with a specific stiffness coefficient. Based on this model, the variation laws of the joint bearing sharing ratio under different internal water pressures, gap sizes, and surrounding rock types were systematically analyzed. The proposed analytical calculation method adopted a framework-based approach. Additionally, supplementary conditions can be incorporated in accordance with the specific engineering characteristics to facilitate targeted analysis. |
|---|---|
| ISSN: | 2096-3246 |