离石地区湿陷性黄土地基强夯参数的试验研究

Experimental research on dynamic compaction parameters of collapsible loess foundation in Lishi region

针对离石地区超高填方下深厚湿陷性黄土地基强夯加固参数及效果开展了系列试验研究,分析了强夯前、后各试验区平均夯沉量和土体主要物理力学指标的变化规律,并给出2 000、3 000、6 000 kN.m能级条件下强夯加固的夯点中心距、最佳击数、停夯标准及有效加固深度等主要参数,在此基础上确定了强夯有效加固深度的估算方法。试验结果表明,离石地区深厚湿陷性黄土地基强夯处理后加固效果显著,有效加固深度范围内黄土湿陷性基本消除;离石或类似地区湿陷性黄土地基采用2 000 kN.m及其以上能级进行强夯处理后,地基承载力特征值均可达到300 kPa以上,土体变形模量大于25 MPa,强夯有效加固深度可采用修正Menard公式进行估算,修正系数可取0.35～0.37;2 000、3 000、6 000 kN.m能级强夯最佳击数分别为11、10、10击,有效加固深度分别为5、6、9 m,夯点中心距分别为4、4、5 m,且分别可将点夯最后两击的平均夯沉量不大于5、5、10 cm作为停夯标准。试验研究成果可为同类工程的设计与施工提供参考。

A series of tests are carried out to study the dynamic compaction parameters and their effects on the deep collapsible loess foundation under super-high fill in Lishi region.Analyses are made on the average settlement of each test area before and after dynamic compaction and on the regularity of the main physical and mechanical indexes of soil.The main parameters are gained,such as the centre distance of dynamic compaction points,the best impact number,the standard of cutting out,and the effective reinforcement depth under the energy levels of 2 000 kN.m,3 000 kN.m or 6 000 kN.m;hence,the empirical formula of the effective reinforcement depth of dynamic compaction is given.The results of the tests show that the deep collapsible loess foundation in Lishi region can be effectively reinforced by dynamic compaction and that the loess collapse in the reinforced range is removed.Moreover,the results show that after dynamic compaction above the energy level of 2000 kN.m,the eigenvalue of the bearing capacity of collapsible loess foundations in Lishi or similar regions can reach over 300 kPa,the foundation soil deformation modulus is more than 25 MPa,and the effective reinforcement depth can be computed by the modified formula Menard,in which the modified coefficient is 0.35-0.37.Furthermore,the results indicate that under the energy levels of 2 000 kN.m,3 000 kN.m or 6 000 kN.m,the best impact numbers of dynamic compaction are 11,10 and 10 respectively;the effective reinforcement depths are 5 m,6 m and 9 m respectively;the optimum centre distances of dynamic compaction points are 4m,4m and 5m respectively;and the average settlements of the last two impacts,which are not more than 5 cm,5 cm and 10 cm respectively,can be used as the optimum standards of cutting out.Therefore,the results of the tests can provide a reference for the design and construction of engineering projects of the same kind.