冻土区输气管道周围土体冻胀融沉研究

FIELD MONITORING FOR FROST-HEAVING AND THAWING-SETTLEMENT OF SOIL AROUND GAS PIPELINES IN PERMAFROST REGION

管道作为油气资源的最为常用的运输方式之一,穿越不同地质情况的区域,所面临的工程问题各有不同。本文对青海省某冻土区输气管道进行调研,针对出现的管沟融陷、工程构筑物冻胀变形等病害问题,选取典型断面,钻孔埋设温度传感器和沉降磁环测试元器件,对暖季和寒季管道周围土体温度和位移进行监测,研究输气管道周围地温变化及冻胀融沉规律,为冻土区输油气管道的设计、施工、运营、病害治理提供借鉴。研究表明:该冻土区寒暖季地表地温随气温波动较大,越靠近管道,地温年振幅越大;该区域冻土地温范围为-2^-1℃,地温带类型属基本稳定带,正温输气的热扰动,导致周围土体融沉;管道正上方受管道放热影响,地温均为正温,影响范围约1.5 m;在近管道处,深度1~4 m,地温受多重因素影响,深度4 m以下,地温年较差较小,均为负温;冻胀由深处向上发生,时间上有滞后性;10月和11月为冻融剧烈时间段,应及时监测预警。

Pipeline is one of the most commonly used methods in petroleum transportation. There are different engineering problems when pipelines go across different geological conditions. In order to solve the diseases like thawing collapse of pipelines and frost heaving of engineering structures,an investigation of gas pipeline was undertaken in a certain permafrost region in Qinghai Province. We selected typical sections and buried temperature sensors and magnetic settlement rings to monitor the temperature and displacement of the soil around pipelines during cold and warm seasons. We studied the law of ground temperature variation around the pipelines and the law of frost-heaving and thawing-settlement,which provides reference for the design,construction,operation and disease treatment of gas pipelines in permafrost region. The studies show that ground temperature changes greatly with the temperature during cold and warm seasons in this area,and the closer to the pipelines,the greater theannual amplitude of ground temperature. The ground temperature of frozen soil in this area is-2 ℃ ~ 1 ℃,which means that the temperate zone belongs to basically stable zone. Heat disturbance of the gas transmission in positive temperature causes the thawing settlement of soil. Due to the heat release of pipelines,ground temperature of the soil above the pipeline turns positive,and the impact range is about 1. 5 m. Ground temperature from 1 m to 4 m under the ground surface is influenced by multiple factors. The annual ground temperature range is relatively small under the depth of 4 m,all of which are negative temperature. Frost-heaving occurs from the depths upwards. There is a hysteresis in time. The freezing-thawing cycle is very severe in October and November and should be monitored in time.