| In recent years,with the rapid development of China’s economy and the continuous improvement of the level of urbanization,more and more high-rise buildings have been built on the weak foundations of karst caves.How to take reasonable measures to strengthen the weak foundation of karst cavity has important practical significance and theoretical value.An engineering project in Baiyun District of Guangzhou is a typical soft foundation of karst cavity.The bad geological effects of karst are strongly developed on the site,and the site stability and suitability are poor.In accordance with the principle of convenient construction,safety and reliability,and economical rationality,high-pressure jet grouting piles are selected to reinforce the soft foundation of the karst cavity of the site.Based on this project,through the collection and analysis of geological survey data,on-site inspection,high-pressure jet-grouting pile reinforcement technical data,and the introduction of theoretical calculations,indoor mix ratio tests,microstructure analysis,geotechnical tests,and stability analysis,this paper establishes a research and application framework for the reinforcement of soft foundations in karst caves with high-pressure jet grouting piles.The main work and research results are as follows:(1)Based on the field survey and considering the complexity of the stability evaluation of the soft foundation of the karst cave,the stability of the soft foundation of the karst cave in the 39 # block of the supporting project was analyzed and evaluated by the qualitative analysis method,semi-quantitative analysis method and fuzzy comprehensive evaluation method.The analysis results show that,on the whole,the soft foundation of the karst cavity on the site of the 39 # block is stable in natural conditions,and the possibility of collapse is small.However,when the excavation and filling construction is completed or in the operation stage,the soil caves and karst caves are easy to cause the ground to collapse and have an adverse impact on the safety of the project.This is a key issue that needs to be considered in the construction of the site.(2)On the basis of the results of the geotechnical tests and the design technical parameters of the high-pressure jet-grouting piles,the unconfined compressive strength tests of the high-pressure jet grouting consolidated body under three different ratios and two curing conditions were carried out.In addition,in order to further improve the understanding of the mechanism of high-pressure jet-grouting pile reinforcement,and explain the macroscopic physical and mechanical phenomena corresponding to the microstructure change process of the high-pressure jet-grouting consolidation,the microstructure analysis of the undisturbed soil sample and the high-pressure jetgrouting consolidation was carried out.The results show that considering the design requirements and the influence of ground water,the cement grout can be designed with the ratio of 35% cementitious material per extension meter.Compared with the undisturbed soil,the microstructure of the high-pressure jet-sprayed consolidated body prepared with different amounts of cementitious materials is more compact.The addition of external cementitious materials adds a lot of fine particles to the surface of the undisturbed soil structure.These fine particles play the role of connecting and cementing the undisturbed soil,and this connection and cementitious effect becomes more and more obvious with the increase of the amount of cementitious materials.(3)The key technologies such as the pre-construction preparation,technological process and construction process parameters of jet grouting piles were elaborated.Finally,the compressive strength test of cement slurry consolidation,core drilling,conventional soil test,and geophysical prospecting were used to test the effect of highpressure jet grouting piles on the soft foundation of karst caves.The test results show that the soil caves and karst caves in the tower area can be filled after being treated with high-pressure jet grouting piles.The fillings of the soil caves and karst caves are denser,and there is no drilling mud leakage problem.The core taking rate in the key areas of the foundation treated by high-pressure jet grouting pile is significantly increased,and the core taking rate in the soil cave and karst cave development area is higher than 90%,which proves that the integrity,stability and continuity of the foundation can be significantly improved after the reinforcement treatment of high-pressure jet grouting pile. |
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