安哥拉红砂现场试坑浸水试验研究

为准确评价安哥拉红砂场地的自重湿陷特征，开展现场试坑浸水试验，对地表及不同深度地层变形、水分入渗规律和浸水前后标贯击数进行监测与研究，并对现场试验与室内试验结果差异性进行探讨。结果表明：浸水后红砂地基表现为持续抬升，变形曲线可分为陡升、缓升、不稳定和趋于稳定4个阶段；深度8 m以上红砂地层为湿陷沉降变形，累计沉降量为5.6 mm,远小于室内试验计算的自重湿陷沉降量137 mm;红砂竖向渗透速率和水平渗透速率均较大，浸水和停水后红砂含水率变化较快，红砂持水性较差，浸水过程中红砂地层的饱和度小于80%,为非饱和渗透；浸水后红砂地层标贯击数显著降低，具有显著的软化特性。红砂较大的渗透系数和较差的持水性导致红砂很难达到饱和状态，是自重湿陷沉降量实测值远小于计算值的因素之一，一般工程建设中建议可不考虑红砂地基的湿陷特性，而将其按软化特性进行设计。研究结果不仅可指导红砂场地未来工程建设，还可为其他砂土湿陷性评价提供借鉴。

Field immersion test on the Angora red sand

To accurately evaluate the self-weight collapsibility characteristics of the Angola red sand site, a field immersion test for monitoring and studying the deformation of ground surface and strata at different depths and water migration regularity was conducted. The standard penetration test (SPT) blow counts before and after immersion were determined, and the difference between the results field and indoor tests was discussed. Results indicate that after immersion, the ground surface of red sand shows continuous uplift deformation. The deformation curve can be divided into four stages: steep rise, slow rise, unstable, and stable. The red sand stratum with a depth of more than 8 m shows collapsible settlement deformation, with a cumulative collapsible settlement of 5.6 mm, which is far lower than the self-weight collapsible settlement calculated by the indoor test (137 mm). The vertical and horizontal permeability rates of red sand are large, and the water content of red sand changes rapidly after water immersion and water cutoff. The water holding capacity of red sand is poor. During water immersion, the saturation of red sand formation is less than 80%, which is unsaturated permeability. The SPT blow counts of red sand formation decrease considerably after water immersion, and softening characteristics are evident. The large permeability coefficient and poor water holding capacity of red sand impede the development of a saturation state, and thus, the measured value of the self-weight collapsible settlement is far lower than the calculated value. In general engineering construction, a design based on the softening characteristics of red sand foundation instead of collapsible characteristics is recommended. The results can not only guide engineering construction in red sand sites but also provide a reference for the collapsibility evaluation of other types of sand.