Abstract: The shallow surface of southwest mountainous cities is mostly soil-rock backfill strata, and the sensitivity law of soil-rock gradation of soil-rock backfill seepage characteristics is difficult to grasp. Under the condition of rainfall infiltration, shallow tunnel and deep foundation pit excavation often induce surface subsidence and slope collapse. Based on the particle gradation of the site soil-rock backfill, the sensitivity of rock content and the loss of fine particles in the permeability coefficient of backfill were studied by indoor constant head test. It is found that the permeability coefficient of soil-rock backfill increases exponentially with the increase of rock content, and begins to increase sharply when the rock content is 60%. Under poor gradation, poor cohesion and adhesion between coarse and fine particles in soil-rock backfill are the main reasons for the loss of fine particles, and the loss of fine particles presents a change process from small to large and then to stable with the extension of seepage time. In practice, the block stone content of the site soil-rock backfill can be reasonably adjusted according to the permeability requirements of the stratum. At the same time, the loss of fine grained soil of the high stone content soil-rock backfill should be focused to ensure the stability of the construction stratum.

Key words: geotechnical engineering; soil-rock backfill; constant head test; permeability coefficient; soil loss

摘要： 西南山区城市浅表多为土石回填体地层，而土石回填体渗流特征的土石级配敏感性规律难以把握。降雨入渗条件下，浅埋隧道及深大基坑开挖多诱发地表沉降及边坡滑塌等灾害。基于现场土石回填体的颗粒级配，通过室内常水头试验对回填体渗透系数的含石量敏感性与细颗粒流失现象进行了研究。发现，土石回填体渗透系数随含石量的增加呈指数形式增长，并于含石量为60%时开始骤增。不良级配下，土石回填体中粗、细颗粒间黏聚性与附着性差是细颗粒流失的主要原因，而细颗粒的流失量随渗流时间的延长呈现由小变大再到平稳的变化过程。实际中可根据地层透水要求合理调整现场土石回填体的块石含量，同时应重点关注高含石量土石回填体的细颗粒土流失问题，以保证施工地层的稳定性。

关键词: 岩土工程；土石回填体；常水头试验；渗透系数；土体流失