堤坝等荷载是分级施加的,地基多是成层的,因此实测的表面沉降–时间曲线是由各级荷载、各层土对应的沉降–时间曲线叠加而成的。理论分析、工程实例表明叠加的沉降–时间曲线通常不是双曲线或指数曲线,在此基础上提出了叠加推算沉降和分别推算沉降的概念。叠加推算沉降误差分析表明叠加推算沉降的误差不但与土层之间的β比值、各级荷载之间的时间间隔有关,而且受沉降推算拟合函数与实际是否相符的影响。β相同的地层可以作为同一层地基,沉降推算采用的拟合函数与实际不同时,分别推算也存在误差。叠加推算的沉降小于分别推算的沉降,通常小于实际沉降。为了减少沉降推算误差,建议尽量利用预压后期的监测数据,并尽可能采用分别推算沉降或采用修正的双曲线法或指数法等。 Dams and other loads are graded, the foundation is mostly stratified, so the measured surface subsidence - time curve by the load at all levels, the corresponding layers of soil subsidence - time curve superimposed. Theoretical analysis and engineering examples show that the superimposed settlement-time curve is not usually a hyperbola or exponential curve. Based on this, the concepts of superposition and subsidence settlement are proposed respectively. The superposition estimated settlement error analysis shows that the error of superposition estimated settlement is not only related to the β ratio between soil layers and the time interval between loads at all levels, but also affected by the settlement to calculate whether the fitting function and the actual fit. The same strata of β can be used as the same ground. When the fitting function of settlement estimation is different from the actual one, the errors are also estimated respectively. Overlaid estimates of settlement less than the estimated subsidence, usually less than the actual settlement. In order to reduce the error of settlement estimation, it is suggested to make full use of the monitoring data of the post-compression period as much as possible and use the hyperbolic or exponential method to calculate the settlement or adopt the correction as much as possible.