| The underwater Quaternary Alluvial-diluvial(Qal+pl)pebble layer is a common geological type in river-crossing bridge foundation.Its soil structure is loose,the length,density and thickness of stones,and the width of soil fissures is uneven and random distribution.Because it is covered by river water,its water content is high and its stability is poor,it can not be used as the sustaining layer of foundation.In order to eliminate the potential engineering hazards of the old bridge foundation,grouting reinforcement can be used to deal with the expansion of the old bridge in such geological strata.After the treatment is completed,it is usually necessary to evaluate the grouting reinforcement area and check whether it meets the design criteria.At present,most of the engineering examples and related engineering experience mainly focus on the test of grouting reinforcement effect,while the review of grouting cement dosage is seldom involved.Grouting construction is a concealed project with many uncertainties.At the beginning of design,grouting cement dosage is estimated mainly by means of pressure water test and geological survey data,which has certain limitations.If supervision information is missing,the final amount given by the construction party is quite different from the design estimate.When the auditor and the construction party do not approve of it,it is necessary to review and evaluate the amount of grouting cement and grouting effect in the grouting area.Taking a bridge consolidation grouting reinforcement project in Guizhou as the test object,this paper designs a set of evaluation methods based on grouting theory and combines field test with laboratory test.A method combining drill core exploration,seismic wave cross-hole CT and chemical analysis is proposed to evaluate the amount of cement used and grouting effect after grouting reinforcement.The method is supplemented by in-situ single-hole grouting test and similar model box grouting test.By comparison,the grouting mechanism of underwater alluvial and alluvial pebble layer is explained from multiple angles,the rationality of the evaluation method is verified,and the cementation degree of the grouting body and the distribution of cement slurry are studied.Finally,the following conclusions are drawn through the study:1.Based on the post-evaluation method designed in this paper,the cement dosage of grouting body in the test area is deduced and its rationality is demonstrated.2.The overall grouting effect of the test area is evaluated.3.Redefining the criterion of CT wave velocity suitable for this geology;4.The distribution curve of cement dosage and CT wave velocity was established.5.The qualitative description of grouting effect is transformed into quantitative evaluation of cement content.6.The relationship between the grouting pressure and the amount of grouting cement is found.The final results show that the evaluation method is reasonable and has good evaluation effect.It can provide technical reference for the cement dosage and grouting effect evaluation of underwater alluvial and alluvial pebble layer after grouting reinforcement,and has certain theoretical and application value. |
