Study On Bearing Characteristics Of Pile Foundation With Side Grouting In Deep Soft Soil

Piles are widely applied to engineering fields, especially in railway and highway, which requires high standards of bearing capacity and settlement. Cast-in-place piles are used more. However, the end bearing resistance and the lateral resistance lose a lot, because of the inherent defect of cast-in-place piles (mud in the end and at side of piles). In order to eliminate the bad influence caused by the mud, post grouting pile foundation, which concludes end grouting, side grouting and end-side association grouting, could be used to improve bearing capacity and to reduce settlement, especially in high-speed railway foundation construction. This paper mainly studied the test of post grouting pile foundation (mainly with side grouting) in deep soft soil. Based on on-site test data and comparative analyses of piles between side grouting and not grouting, this dissertation draws the pile foundation with side grouting has the following advantages.1. The obviously improvement of bearing capacity; 2. The smaller total settlement; 3. The rapider to reach a unchangable settlement. Therefore, owing to side grouting in deep soft soil, bearing characteristics of super-long drilling piles are improved obviously, especially in effectively improving bearing capacity and reducing settlement of pile foundation.The bearing capacity of foundation is usually an important controlling factor for the high-speed railway construction in deep soft soil. So it is very important to make sure the size of bearing capacity of pile foundation for the design of high-speed railway. According to the test data, the lateral resistance dominants the bearing capacity of super-long pile foundation, while resistance in the end of piles holds a small proportion, which is about ten percent of total load. So in deep soft soil they are frictional pile foundations. At present, there are some calculative methods of the bearing capacity of frictional pile foundation, but any kind of method has its own advantages and disadvantages, also the different applicable scope and the computational accuracy. This paper will calculate the maximum bearing capacity of frictional pile foundation by four standard methods and the numerical simulation. After the comparison of these methods, the following conclusions are drawn.1. Different methods, different calculative results. So the method which calculates the bearing capacity of pile foundation with side grouting needs to be suitable and to be according with the actual situation.2. The method called pier base method is not suitable, because of its exaggerated the end bearing resistance. So does the method, named entity deep foundation method, which is suitable for calculating the lateral resistance.3. The numerical simulation can be obtained satisfying results, if parameters are selected accurately. Its shortcoming is that the simplification in modeling process leads to be different from actual situation.4. The method in "Technical Code for Building Pile Foundations" considering the effect of side grouting comprehensively is an corresponding method,which is suitable for actual situation in total shaft resistance, total tip resistance and the share of load on the bottom of cap. Therefore, the method in "Technical Code for Building Pile Foundations" is recommended as the suitable method for calculating the maximum bearing capacity of frictional pile foundation with side grouting in deep soft soil.