STRESS-STRAIN STATE OF UNDERGROUND PLASTIC PIPES

Аннотация

This article examines the features ofthe stress-strain state(SSS) ofplastic pipes used in underground utilities. Factors of external load from the soil, as well as the characteristics of the pipe material (PE, PVC, etc.) are taken into account. Methods of numerical and experimental analysis of SSS are given, modeling results are presented, and recommendations for improving thereliability ofsystems are given.. 1. Introduction. In recent decades, plastic pipes have become widely used in the construction of underground utilities, such as water supply, sewerage, drainage and gas distribution systems. The most common materials used to manufacture such pipes are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and cross-linked polyethylene (PEX). These materials have a number of operational advantages over traditional metal and reinforced concrete analogues, including: •high corrosion resistance; •light weight and ease oftransportation; •lowthermal conductivity; •smoothinner surface that reduces hydrauliclosses; •resistance to aggressive chemical environments; •durability (service lifeof 50years ormorewith proper installation and operation). However, despite all the advantages, plastic pipes in underground conditions are exposed to significant external loads, themain sources ofwhich are: •pressure from thesoil's own weight and from overlying layers; •temporary loads from vehicles (in case ofshallowbackfill); •internal pressure of liquidorgas; •soilmovements and settlements (for example,inseismically active zones orduring freezing). Under the influence of these factors, a complex stress-strain state (SSS) occurs in the pipe body, characterized by bends, crushing, stretching or compression of the pipe walls. If permissible stresses are exceeded, cracks, loss of tightness, ovality and other defects may appear, leading to failure ofthepipeline. Considering the behavioral characteristics of plastics as time-dependent and nonlinear materials, it becomes especially important to conduct an accurate analysis of the stress-strain state of pipes under real operating conditions. The purpose of this work is a comprehensive study of the stress- strain state of underground plastic pipes using both analytical and numerical methods, as well as the formulation of recommendations for their reliable design and operation. The purpose of this article is to analyze the stress-strain state of plastic pipes during underground installation and to develop recommendations for theirsafe operation. Theoretical bases of stress-strain state analysis. Stress-strain state (SSS) analysis of underground plastic pipes requires taking into account many factors, including pipe geometry, physical and mechanical properties of the material, soil type, installation conditions and the nature of the 188 INTERNATIONAL MULTIDISCIPLINARY JOURNAL FOR RESEARCH & DEVELOPMENT SJIF2019:5.2222020:5.5522021:5.6372022:5.4792023:6.5632024:7,805 eISSN:2394-6334 https://www.ijmrd.in/index.php/imjrd Volume12,issue06(2025) external load. A special feature of plastic pipes is their ability to undergo significant elastic and creeping deformations, which distinguishes them from metal orreinforced concrete analogues. Factors influencing theSSS ofplasticpipes Themain factors determining the stress-strain state ofplasticpipes include: • Permanent loads from themass of the soil: depend on the depth of backfill, density and moisture ofthesoil. •Temporary loads: impact from vehicles, vibrations, dynamicloads. •Internal pressure: in thecase ofpressure pipes, creates radial andtangential stresses. • Creep of the material: over time, even under constant load, plastic pipes deform, which is important totake intoaccount duringlong-term operation. Mechanical properties and modeling of material behavior Plastics used in pipeline systems are time-dependent (viscoelastic) materials. Their behavior can bedescribed usingmodels: •Linear elasticity (in theearly stages or underlowloads); •Viscoelasticity (Maxwell model, Kelvin-Voigt, etc.); •Nonlinear plasticity(under large deformations orlong-term loading); •Creep and stress relaxation (important during long-term operation under constant load). The use of mathematical models and numerical methods, such as the finite element method (FEM), allows us to obtain an accurate distribution of stresses and strains in the pipe wall, as well as toassess its stabilityandresidual life. Boundary conditions and loading schemes When calculating the strength ofpipes, it isnecessary to takeinto account: •Typeof pipesupport (rigid foundation, sand backfill, soft soil); • Nature of interaction with the surrounding soil (models of "pipe-in-environment", interaction according to Winkler's law, etc.); •Presence ofprotective backfill (improves stress redistribution); •Consideration ofthering stiffness ofthepipe(important for resistance to external pressure). Such a comprehensive assessment allows identifying the most stressed areas and taking engineeri