大厚度自重湿陷性黄土场地湿陷变形特征的大型现场浸水试验研究

结合国家重点工程建设项目--宁夏扶贫扬黄灌溉工程11号泵站地基的预浸水处理,在自重湿陷性黄土厚度大于35m的场地上做了面积为110×70m2的浸水试验,试验历时251d,揭示出大厚度自重湿陷性黄土的湿陷变形具有与中小厚度(小于15m)自重湿陷性黄土的湿陷变形不同的3个显著特征:①湿陷量随浸水历时的发展过程包含5个阶段,即初期平缓段、浸水陡降段、中期平缓段、停水后的陡降段和后期平缓段;②湿陷速率在浸水期间呈显“小→大→小→稳定”的变化规律,在停水后则呈显“大→小→稳定”的变化规律;③湿陷量、试坑周边裂缝的宽度和裂缝两侧地面的高差远远大于既往同类研究记录。通过分析,建议把连续5d的平均湿陷量不大于2mm作为大厚度自重湿陷性黄土场地浸水试验的停止注水标准;采用建议的停水标准,缩短了该建设项目的工期、节省了费用。本文的研究成果可供今后类似的地基处理工程及修订黄土规范参考。

Large area field immersion tests on characteristics of deformation of self weight collapse loess under overburden pressure

A large area field immersion test with water pool of 110×70 m2 was conducted combining with ground treatment of the eleventh pump station using prewetting method.Building the pump station was a national key construction project of the Yellow River for irrigation in Ningxia province,China.The soil stratum of test site was self weight collapse loess with a thickness of 35 m,and the test was sustained for 251 days.It was shown that there were three distinct characteristics of the collapse deformation of the self weight collapse loess with big thickness(i.e.,more than 15 m)different from that with middle-small thickness(i.e.,less than 15 m):① The process of collapse settlement developing with immersion time consisted of 5 stages,i.e.,initial gentle change,abrupt increasing,smooth progress,fast enhancement after cutting off water,and slow variation.② The rate of collapse settlement varied with immersion time in such patterns:low,high,low and gentle;After cutting off the water supply,the rate of collapse settlement appeared with time in such fashions:large,small and gentle.③ The collapse settlement,the width of the crack and the level difference of two sides of the crack around the test site were much larger than the corresponding record of the similar tests in the past and in other regions of China.A criterion for stabilized collapse settlement and cutting off the water supply was proposed via analysis of the results of the field immersiontests in the past years and in other regions of China.The proposed criterion was that the rate of collapse settlement was not larger than 2 mm/d for 5 days in succession.The time limit and investment for the project was reduced because of adopting the criterion.The research results might be useful to similar projects and to revise “Code for building construction in collapsible loess regions”.