| In housing construction,municipal road traffic and bridge engineering,pile foundation is the most widely used foundation form.According to incomplete statistics,the various piles used in China in the past 20 years amount to tens of millions.Due to the complicated geological conditions,the design and construction of pile foundation bring many hidden dangers.Especially for the karst area,because the karst geological conditions are very complex and there are many influencing factors,it is the design and construction of buildings and substructures that bring great safety hazards.At present,China's research on the vertical bearing capacity of pile foundation in karst areas is still in the exploratory stage and it is still the leading method of pile foundation design in karst areas,and too conservative design inevitably leads to waste in engineering.Different roof thickness of karst caves will have a great impact on the ultimate bearing capacity of foundation piles,so the ultimate bearing capacity of rock-socketed piles and the safety thickness of karst roof in karst areas are the key technical problems that need to be solved urgently.In this paper,the bearing capacity of rock-socketed piles has been studied and discussed,especially the design and construction of three engineering piles in the karst cave area have been studied theoretically,experimentally and calculated,and good results have been obtained.The work and innovations are as follows:1.First,in view of the unclear calculation method and bearing mechanism of rock-socketed pile,the current design specifications for pile foundation are described in this paper: Specification for design of building foundation "and" code for building pile foundation technology,"the highway bridge standard about foundation and foundation design","code for building pile foundation technology,specifications for design of building foundation bearing capacity of rock-socketed piles,this paper analyzes the calculation method and comparative analysis,and combined with the test specification standard building building foundation of guangdong province based on the ultimate bearing capacity of pile detection,put forward a kind of vertical ultimate bearing capacity of rock-socketed pile calculation method,and applied to the karst region,make up for the deficiency of the currentspecification,provide reference for construction and design.2.In view of the design process of rock-socketed piles in karst areas is too conservative,such as through caves,etc.,theoretical analysis is made on the bearing capacity of rock-socketed piles through caves and pile ends placed on the roof,so as to obtain the influence of rock-socketed piles through caves on bearing capacity,and a more reasonable design method of rock-socketed piles in karst areas is proposed.In view of the current situation of "see hole and wear",put forward reasonable Suggestions on whether to run through the cave.3.Entrusted by guangzhou expressway company,the bearing capacity analysis and static load test of three engineering piles in the karst region of huadu district,guangzhou were studied.The rock-socketed piles at ordinary rock-socketed piles and karst caves were selected for experimental study.Based on the results of this experiment,comparison and analysis are carried out,and comparison is made with theoretical analysis to more intuitively reflect the lateral resistance process of pile-rock interface and the interaction between pile and karst cave.The difference of bearing capacity between theoretical analysis and test results is small.4.Karst region on the bearing capacity of rock-socketed piles mode and the main components of controversial issues,based on the measured results and the rock mechanics parameters,the factors such as thickness,roof rock-socketed depth,side-rock interface friction resistance is put forward to karst area is an important part of the bearing capacity of rock-socketed pile,draw rock-socketed piles in-side of rock interface friction resistance proportion of total lateral resistance and three engineering piles are 50%,19.8% and 32.9%respectively,engineering pile after entering the bedrock,axial stress of pile fell sharply,and the basic linear downward trend.5.Aiming at pile end underlying caves need no stress distribution state of conservative design and karst roof failure mechanism,as well as the rock-socketed pile embedded in period of the lateral resistance of the characteristics of big proportion of analysis conforms to the load-bearing characteristics of rock-socketed pile considering rock the lateral resistance of karst roof failure model,rock-socketed pile safety evaluation in karst area,provide usefulsuggestions for construction and design.6.Based on the static load test of pile foundation in karst areas,the lateral resistance,rock-socketed end friction and pile end resistance effects of rock-socketed piles in karst areas are studied to obtain the bearing capacity characteristics of rock-socketed piles in dissolved areas,so as to scientifically obtain the load sharing effect of karst cave roof.After the load force of karst cave roof is obtained,the lateral resistance of rock-socketed pile and the resistance of pile end are taken into account together with the reaction force of lateral friction resistance(shear force)of karst roof pile and the resistance of pile end,and the roof stability of karst cave is calculated.The calculation model is more consistent with the actual stress of karst cave roof and more scientific and reasonable. |
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