4.11　Soil-lime Compacted Columns

4.11.1　The tube sinking method，impact method or drilling method shall be selected for soil-lime compacted columns according to design requirements，soil conditions and surrounding environment.

4.11.2　Construction of soil-lime compacted columns shall be in accordance with the following sequence：

1　The site shall be levelled and the column holes shall be positioned and numbered before the construction；

2　The whole site treatment should proceed from the inside out and local treatment should proceed from the outside in；the treatment shall be conducted every other 1 holes-2 holes successively during construction；

3　The holes shall be backfilled and compacted timely upon reaching the required depth.

4.11.3　The soil material of soil-lime compacted columns should be silty clay excavated from the foudation trench on site or nearby.The lime shall be fresh lump lime of GradeⅢand above；prior to use，the lime shall be slaked and sieved and its particle size shall not be greater than 5mm.The mix proportion of soil and lime by mass and volume shall meet those specified in 4.2.1.

4.11.4　During tamping and backfilling of column holes，the water content of backfill materials should be controlled within±3% of the optimum water content，and the dry density after tamping shall not be less than the arithmetic product of its maximum dry density and compaction coefficient required in the design.The optimum water content and maximum dry density of the backfill materials may be determined through compaction test.

4.11.5　Prior to backfill，the hole bottom shall be compacted，and random inspections of hole diameter，depth，verticality and position toleranceshall be performedin accordance with the following requirements：

1　The tolerance of column hole diameter shall not be greater than 5% of column diameter；

2　The tolerance of column hole depth shall be±500mm；

3　The verticality tolerance of column hole should not be greater than 1.5%；

4　The column position tolerance should not be greater than 5%of column diameter.

4.11.6　The column holes，after passing the inspection，shall be backfilled with sieved soil，lime soil or other backfill materials in lifts according to the design requirements，and shall be compacted in lifts to the design elevation.

4.11.7　The construction quality inspection of soil-lime compacted columns shall meet the following requirements：

1　The construction quality shall be subjected to random inspection upon completion of columns and the random inspection quantity shall not be less than 1%of the total number of columns；

2　Upon completion of columns，the construction records as well as the dry densities of columns and inter-column soil within the full treatment depth shall be inspected and then shall be converted to average consolidation coefficient and average compaction coefficient.