从实测沉降过程推算固结系数

按照Terzaghi固结理论,直接从土体压缩时间过程定出控制孔压消散速率的固结系数,暗含固结度U_σ和压缩度U_ε等同的假设。由于土的应力应变关系是非线性的,所以U_σ和U_ε并不等同。在应力增量（△p/p）较大时,特别是对于高压缩性的软粘土来说,上述假设可能引起相当大的误差。本文采用双曲线型和半对数型的压缩曲线,推导出固结度U_σ和压缩度U_ε之间的两种解析关系,并提出从实测沉降过程推算现场土层平均固结系数的方法。经工程检验,证明从双曲线型压缩曲线求出的U_σ和U_ε之间的关系优于从半对数型压缩曲线求出者。最后指出,只须对古典固结理论中的线性化假设作出适当修改,从假设固结过程中土的压缩性m_υ和透水性k不变,改为假设固结系数C_υ或C_h不变（k/m_υ=常数）,则在采用非线性应力应变关系时,仍能运用古典理论进行计算。这样,就可避免那种明显不合理的U_σ和U_ε等同的假设,使实用时的误差大大减小。

Derivation for Coefficient of Consolidation from Settlement Observation

Based on the Terzaghi’s theory of consolidation, it is used to derive, directly from the time-compression curve of soil, the coefficient of consolidation which controls the rate of dissipation of the excess pore pressure. An assuumption is implied in this procedure that the degree of consolidation Uσ is equivalent to the degree of compression Uε In fact, owing to the non-linear stress-strain relation of soil, Uσ and Uε are not exactly the same in general. Two kinds of analytical relationship between Uσ and Uε are derived on basis of compression curve of hyperbolic and semi-logarithmic type respectively, and thence a method to predict the coefficient of consolidation for the in-situ soil from the settlement observation is proposed. It is shown by the calculation of a case record that the relation between Uσ and Uε obtained from the compression curve of hyperbolic type is preferred to that from semi-logarithmic type. This is mainly because that the shape of the compression curve of soil fits in better with the hyperbolic than with the semi-logarithmic equation.