考虑预固结时堆载预压卸载的沉降标准

为了分析预固结和次固结对堆载预压期的影响,依据Bjerrum等时间线蠕变图和Yin-Graham一维弹黏塑性模型(EVP模型),根据运行期限和允许沉降量等技术参数获得等、超和欠载预压卸载时的临界孔隙比,由此可计算决定等、超和欠载预压卸载时机的临界沉降量,并根据欠载预压的临界孔隙比公式计算出最小预压荷载,克服传统堆载预压依据主固结理论无法反映堆载预压和天然软土预固结效应降低次固结变形的缺陷.在考虑天然软土存在预固结效应情况下,证明新假说A与假说B存在近似等价的充分条件.算例表明,在计算堆载预压卸载时的临界沉降量和地基总沉降量时不能忽略天然软土预固结效应的影响.

Settlement standard of unloading time for preloading method with an eye to pre-consolidation time

In order to analyze the effect of clays aging preconsolidation and creep on preloading period, based on Bjerrums equal time lines creep diagram and Yin Grahams 1 D elastic viscoplastic model( EVP model ), the critical void ratios of unloading time in the preloading method including equal preload and surcharge preload and undersurcharge preload were derived from technical parameters such as service life duration and allowable settlement. The critical settlements of unloading time werefurther determined by the critical void ratios of unloading time for equal preload and surcharge preload and undersurcharge preload, and the corresponding minimum preload was decided by the formula of critical void ratio for undersurcharge preloading method. It overcomes the flaws that the classical preloading method based on primary consolidation theory could not reflect the mechanism that preloading method and the aging preconsolidation of natural clay  reduces secondary consolidation compression. Taking account of the aging preconsolidation of natural clay, the sufficient condition is proved that the modified hypothesis A is approximately equal to hypothesis B. The examples show that the aging preconsolidation effect in natural clay cannot be negligible in the critical settlement calculation of unloading time in the preloading method and the total settlements calculation of soft ground.