| Yellow River Embankment is the longest river embankment in China,and is mainly constructed of Yellow River alluvial soils.The poor properties of Yellow River silt bring lots of hidden dangers to embankment engineering of the Yellow River.Among others,impervious reinforcement of the embankment is one of the critical issues in the lower Yellow River.Among the potential seepage control methods,fracture grouting has beendeveloping rapidly recently due to its simple application procedure and high efficiency.However,there is currently a lack of systematic investigations studying the anti-seepage effect of the fracture grouting employed in this longest river embankment in China.During the project named ’The research and demonstration of plain reservoir’s health diagnosis and protection technique during its operation period in the south-to-north water diversion project’,laboratory test,in-situ experiment and numerical simulation were carried out to investigate the reinforcement effect of fracture grouting in the Jinan section of the Yellow River Embankment.In particular,laboratory tests concentrated on studying the properties of the Yellow River silt,and the optimum property improvement for cement-silicate grout by varying the content of backfilled fly ash and bentonite as admixtures.Mechanical strength and SEM photographs were investigated for assessing the strength and compactness improvement.Subsequently,based on the obtained optimum admixtures content,in situ grouting tests were carried out in the Jinan section of the Yellow River Embankment to investigate the diffusion process of cement-silicate grouts and evaluate the reinforcement effect of fracture grouting,where geophysical prospecting(including GPR and HDRM)and pit prospecting methods are employed.Finally,according to the actual distribution of grouting veins,ABAQUS software was employed to analyze the reinforcement effect of fracture grouting by comparing the changes of pore pressure,seepage direction and seepage discharge before and after grouting.Based on the experimental and numerical results,the following conclusions can be drawn:(1)Based on the soil tests,the Yellow River alluvial soil in the Jinan section can be classified as low liquid limit silt with poor gradation.In addition,the permeability of the Yellow River silt is relatively low according to permeability test.(2)Compared with pure cement-silicate grouts,the gelation time of the improved slurry is more adjustable when backfilling different percentage of fly ash and bentonite.When the mixing proportion of the compound cement-silicate grout is 70%cement.25%fly ash,5%bentonite,and the volume ratio is 2,the mechanical strength and compactness of concrete are optimum for the investigated cases.(3)Good agreement is found between the ground-penetrating radar and high-density resistivity method,and the prospecting results also show good agreement with the actual reinforcement effectiveness.Therefore,the two geophysical prospecting methods can both reflect the anti-seepage effectiveness of fracture grouting on site.(4)Grouts mainly flow along the axial direction of the embankment,which manifests that the treatment used to generate directional fracture is proven to be effective.The injected hole distance is suggested to be 1.2m,where the lapping effect of the grouting veins is relatively significant.The averaae thickness of the grouting veins is approximately 5.8cm and the corresponding permeability coefficient is averagely 1.6xX10-6 cm/s,which meets the anti-seepaae criterion in practice.(5)The numerical result shows that the total pore pressure in upstream/downstream after grouting is linearly distributed in certain depth.The flow velocity of water is much smaller than that before grouting when observing the flow vector.More importantly,the seepage discharge after grouting is only one sixth of that before grouting.To sum up.the anti-seepage effectiveness is remarkable within the range of grouting veins and the reinforcement effect of fracture grouting is significant. |
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