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钱塘江冲海积粉土以砂质粉土为主,呈“高粉性、低黏性”的地区特点,在地下水动水压力作用下极易产生渗透破坏。粉土是介于砂性土和黏性土之间的一种过渡类型土,工程性质既与砂性土不同又与黏性土有较大区别。采用自行研制的粉土抗渗强度测定设备,对钱塘江冲海积粉土5种典型样本和微层理原状样本进行了渗透稳定试验。结果表明,钱塘江冲海积粉土渗透稳定性差,抗渗强度低;砂质粉土临界水力比降i_(cr)为1.01~1.25,破坏形式为局部流土,从临界水力比降i_(cr)发展到破坏比降i_F的过程是瞬间的,基坑开挖遇到该类土层极易产生渗透破坏;黏质粉土临界水力比降i_(cr)随黏粒含量增加而增加,从临界水力比降i_(cr)发展到破坏比降i_F有个短暂的过程,是整体流土破坏;钱塘江冲海积粉土渗透稳定各向异性;渗流垂直微层理方向的临界水力比降i_(cr)最大,是渗流沿微层理方向i_(cr)的2.5倍左右。研究结果为粉土地基渗透破坏防治提供参考。
The sedimentary silt in the Qiantang River is dominated by sandy silt, presenting the characteristics of “high-powdery and low-viscosity ”, which is prone to infiltration and destruction under the hydrodynamic pressure of groundwater. Silt is a kind of transitional soil between sand soil and cohesive soil. The engineering property is different from sandy soil and cohesive soil. Using self-developed soil anti-seepage strength measuring equipment, five kinds of typical samples of micro-stratification of Qiantangjiang stratum silt and the original sample of micro-stratification were tested. The results show that the infiltration stability of Qiantang silty sea silt is poor and the anti-seepage strength is low. The critical hydraulic ratio drop of sandy silt is 1.01-1.25, and the failure mode is local flowing earth. From the critical hydraulic ratio i_ ( cr) to the destructive ratio i_F process is instantaneous, the foundation pit excavation encountered such a soil prone to infiltration and destruction; clayey silt critical hydraulic ratio drop i_ (cr) with the clay content increases, From the critical hydraulic ratio i_ (cr) to the destructive ratio i_F, there is a transient process, which is the whole soil failure; the anisotropy of Qiantang sea-flowing silt is permeable; the critical hydraulic ratio The maximum i_ (cr) is about 2.5 times of the i_ (cr) along the micro-lithology direction. The results provide a reference for prevention and control of seepage failure of silt foundation.