南水北调中线总干渠磁县段的地基土具有中等震动液化现象，如处理不当可能导致渠道沉陷甚至滑坡，危及渠道安全。设计采用夯扩挤密碎石桩进行地基处理，为此需在现场选取有代表性的场地上进行试桩，通过试验验证不同桩间距对砂土液化的处理效果，以确定合适的桩间距，为大面积施工提供有关参数和依据。夯扩挤密碎石桩利用重锤冲击成孔，分层填入碎石或其他置换料，并夯击至设计标高。试验表明，采用桩间土标准贯入试验可判断经处理后的地基土，桩间距为1.8m时不存在液化，桩间距为1.9m时存在液化。原位跨孔剪切波速试验结果显示，处理后桩间土的剪切波速较地基处理前提高较多，证明挤密效果明显。

Foundation soil of Ci-Xian section of the main canal in the Middle Route of South-to-North Water Transfer Project has medium liquefaction phenomenon. Canal subsidence and landslide can happen if the foundation soil is not treated properly, which can affect canal safety. The ram-compaction gravel piles can decrease sand ground liquefaction. In-situ pile test needs to be conducted. The effects of different pile spacing on treatment of sand liquefaction were tested to determine the appropriate pile spacing, which can support the design parameters and principle for pile construction in a large area. The ram-compaction gravel piles used heavy hammer impact to form the hole, and then filled in gravel or other replacement materials in each layer to reach the design height. The results showed that ground liquefaction is not shown when the pile spacing is 1.8 m but occurs when the pile spacing is 1.9 m. In addition, the shear wave test of original crosshole showed thatthe shear wave velocity of soil among piles increases after the treatment, which indicated the compaction effect is significant.