注浆法应用于局部非饱和黄土地基中的适用性

Applicability of Grouting Method in Local Unsaturated Loess Foundation

为了探明注浆法应用于黄土地区某既有高层建筑地基加固产生负面作用的原因,用以指导该建筑物进一步的加固工作。依托某建筑物纠偏工程讨论了注浆法在局部非饱和黄土地基中的适用性。采用现场监测方法对建筑物的沉降、倾斜以及地基土孔隙水压力指标进行了监测,结合地质条件以及前期加固方案,分析了注浆后地基土承载力不升反降、建筑物沉降速率增大的原因。结果表明:注浆开始后,建筑物沉降速明显增大,且南侧高于北侧,随着施工的暂停和恢复,沉降速率随之减小和增大。最大沉降速率达2.05 mm/d,南北两侧最大沉降差达40.78 mm。孔隙水压力变化趋势与沉降速率类似,最大孔隙水压力达990.21 kPa。停止注浆后,地基南侧各处孔隙水压力有所降低,降幅8.85%~45.56%。注浆使建筑物产生不均沉降的原因为,未凝结浆液中的水在注浆压力和较高的孔隙水压力作用下逐渐渗透到本就排水条件不良的地基土中,且由于地基内初始孔隙水压力及初始排水条件的差异,对地基产生了不均匀的影响,最终体现在建筑物不均匀沉降上。可见对于类似的排水条件不良且孔隙水压力过大的局部非饱和黄土地基,注浆加固前应采取打入排水板、泄压孔等措施消散孔隙水压力,然后再进行注浆施工。

To determine the causes of the grouting method's unfavorable impact on the foundation reinforcement of an existing high-rise building in the loess area and to serve as a guide for the building's additional reinforcement.Based on a building rectification project,the grouting method's applicability in a local unsaturated loess foundation was explored.On-site measurements were made of the building's tilt and settlement as well as the pore water pressure index of the foundation soil.The reasons for the rise in the foundation soil's bearing capacity and the building's settlement rate after grouting were examined in conjunction with the geological circumstances and the earlier reinforcement plan.The results show that the building's settlement rate clearly increases at the start of grouting and is higher on the south side than the north side.The settlement rate decreases and increases as construction is halted and resumed.The maximum settlement difference between the north and south sides is 40.78 mm,and the maximum settlement rate is 2.05 mm/d.The maximum pore water pressure is 990.21 kPa,and the variation trend of pore water pressure is similar to that of settlement rate.The pore water pressure on the south side of the foundation decreased by roughly 8.85%~45.56% after grouting was stopped.The water in the uncondensed slurry gradually penetrates into the foundation soil with poor drainage conditions under the action of grouting pressure and higher pore water pressure,as well as the initial pore water pressure and initial drainage conditions in the foundation.This is the reason for the uneven settlement of the building caused by grouting.The difference has an uneven impact on the foundation,which ultimately manifests itself in the building's uneven settlement.As can be seen,measures like drilling drainage plates and pressure relief holes should be taken to relieve excessive pore water pressure before grouting reinforcement,and then grouting construction should be carried out,for similar local unsaturated loess foundations with poor drainage and excessive pore water pressure.