| Karst stratum is a common type of regional geology in China,and it is more prominent in certain areas.The rock and soil environment in karst area is relatively fragile,and there are often different degrees of geological problems in the construction site and surrounding areas,such as hydrogeological structure system disorder,soil erosion,landslide and ground collapse.Due to the complexity of karst geology and the limitation of exploration methods,the construction process of rock-socketed piles often encounters problems such as pile hole collapse,excessive depth of foundation pile into rock and increasing cost.The quality problems of pile foundation in karst areas are often caused by imperfect technical control and measures.Therefore,how to use effective exploration means to find out the development characteristics of karst caves in karst foundation,improve the safety evaluation method of rock-socketed piles,pile foundation construction quality control technology,and high-quality construction of subway cover property on karst foundation has important practical significance and practical value.Based on the study of common exploration methods,pile construction methods and applicability of rock-socketed pile engineering site in karst foundation,taking the property construction project of Yinshan depot of Xuzhou Metro Line 3 as the research background,this thesis carried out a series of research on geological exploration technology and rock-socketed pile foundation construction control technology in karst development area.The research shows that scientific and reasonable construction of subway cover property requires a variety of exploration methods to comprehensively reveal the stratum,so as to explore the hydrological and engineering geological conditions of the construction site and the distribution and development of karst caves,and ensure the safety of rock-socketed pile construction.In this thesis,FLAC 3D is used to simulate the construction of pile foundation in karst area of background engineering.The influence of karst location,karst cave size,pile diameter,pile distance and pile hole offset distance on the bearing capacity of pile body and the stability of karst cave roof are analyzed.When the thickness of cave roof changes,with the increase of roof thickness,the roof settlement shows a decreasing trend.The maximum displacement of the cave roof is 0.49 mm in the middle position.This simulation can better reflect the actual situation.Combined with the applicability analysis of existing codes,considering the safety and economic factors of pile construction,the suitable rock-socketed depth of pile foundation for background engineering is proposed by numerical analysis.The research shows that the appropriate rock-socketed depth of the foundation pile in the background engineering is 2.5 m(2.5 times the pile diameter),and the distance between the pile foundation and the cave top is 3.5 m,which can ensure the stability of the cave.The influence of cave span,roof thickness and the number of caves around pile foundation on the ultimate bearing capacity of roof is obvious.The number of caves around pile foundation is inversely related to the ultimate bearing capacity and pile displacement.The applicability of pile foundation detection technology and the factors affecting pile quality are analyzed.The measured values of pile foundation construction in background engineering meet the relevant specifications and design requirements.Through the numerical simulation of the relationship between cave roof and pile foundation construction,the qualitative analysis method is used to set the quality management objectives,analyze the causes of the problems and study the quality control measures.The defects of some type II piles and the causes of the defects are studied,and the technical measures of pile quality control in the construction process are put forward : when the existing span and cave size are large,the grouting method can be used to strengthen the cave area;during pile foundation construction in small karst area,steel casing can be used to follow up,so as to control the influence of karst strata on pile quality to the greatest extent.The research results provide technical basis for systematically establishing the karst foundation exploration method system of the property construction site on the subway,and scientifically and reasonably carrying out the design calculation and construction management of rock-socketed piles in karst foundation.This thesis has 25 figures,27 tables and 91 references. |
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