breaking hardpan敲碎硬盘
humus hardpan腐殖
hardpan roughness沟底不平度
lime hardpan石灰硬盘
hardpan dynamiting底土爆破
gravel hardpan砾石硬层
calcareous hardpan石灰硬盘
get down to hardpan讨论基本问题
N（名词） a hard impervious layer of clay below the soil, resistant to drainage and root growth 硬质地层