n. hardpan
misc. gravel bed
小石头、砂砾层也可用来做隔绝层，以保持水分，降低土壤的温度。
Pebbles and gravel also insulate the soil to keep surface temperatures low and preserve water.
对冻结风化基岩、砂砾层或卵石层，冻土挖掘机效率低，宜采用钻眼爆破法，采用抓岩机装载冻土。
For the frozen weathered bedrock, sandy gravel and pebble bed, it is more suitable to use drilling and blasting method than to use the frozen soil excavator.
砂砾层，水泥稳定石层，和混凝土层的厚度仅供参考，最终将根据中国规范精确的测算出其各自厚度。
The gravel, grave cement and concrete thickness are given for reference only; the final thickness will be accurately calculated according to Chinese regulation.
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