基坑降水中渗流破坏归类及抗突涌验算公式评价

Classification of seepage failures and opinion to formula for check bursting instability in dewatering

基坑降水工程中的渗流引发一种体积力即渗流力,尤其当坑底下覆承压含水层时可能引发以下渗流破坏现象如流砂、管涌、坑底突涌安全等,需要进行安全验算。以力的性质将安全验算分为2种判别标准:一种为面积力安全验算,另一种为体积力安全验算。对于抗突涌安全验算公式,在目前规范公式的基础上考虑了被浮托土块侧面抗剪强度安全储备的发挥,并结合天津市区内典型地铁车站基坑几何性状和取值极为保守的土性参数进行验算,结果表明抗剪强度可发挥至少1/4以上抗突涌贡献,对于基坑下呈透镜体状分布局部承压砂层,发挥作用更大。如考虑抗剪强度发挥减少井孔数量,既可节约工程费用,又可减少钻孔处的安全隐患。

During dewatering in an excavation for a building pit, the seepage force or high pore pressure in confined aquifer lying under the bottom of the excavation may lead to seepage failure such as： boiling, piping and bursting. Dewatering lowing the hydraulic pressure and bring the volume force： seepage force, classification for the seepage failures was made by the essence of the force, boiling and piping because of plane force, bursting because of volume force, At present the formula to check bursting safety only compare the gravity of soil body and hydraulic pressure under the soil body, doesn＇t consider the shearing strength. Taking the shearing strength into consideration, using the typical excavation engineering data in Tianjin＇s metro station pit, after calculating the balance of upward force and downward force, it is found that the sheafing strength surrounding the soil body is about quarter to half by portion of upward hydraulic pressure. Especially for lenticular interbed, the shearing strength is more safe against the upward hydraulic pressure.