The Technique Of Pressure Grouting Under Piles' Tip And Applying To Cast-in-Situ Piles In Gravel

Today, cast-in-situ piles are more widely used in deep foundation engineering because of their many advantages, such as better adaptability to various ground condition, providing enormous bearing capacity by a single pile and smaller dosage of reinforcing steel bar.But,their own disadvantages, such as sediment under tip, clay slurry around pile, friction and tip resistance disagreement and initial ground stress freeing, limited their bearing capacity, lowered the utilization ratio of material and increased the settlement. Applied to cast-in-situ pile, the technology of pressure grouting under pile's tip can increase pile's bearing capacity largely and the utilization ratio of material, and decrease its settlement. Furthermore, this technique is better adaptable to various soil stratum and can make magnificent economic efficiency with simple facilities and construction method.On the other hand, gravel ground condition is a good bearing stratum for piles, which is often met with in civil construction. However, there are many troubles in constructing in gravel, such as drilling difficult, hole collapsing and drill losing, which will lead to enlarge or shrink pile's diameter, form fault pile, delay the time, increase the use of material and higher the investment. Once the grouting technique being applied, diameter and length of pile can be decreased. Pile's tip can be directly laid in gravel and construction work can be cut down, which means lower construction difficulties and less expenditure.On the basis of in-site test of piles in two great bridges in one expressway project, this paper investigates the application of this technique applying to cast-in-situ pile in gravel, studies the bearing properties of grouted piles, examines the practicality of high-strain test use in grouted piles and analyses the grouted piles with Vesic Theory. In addition, based on the research of this technique in recent years, combined with in-site test result, this paper puts forward the design and calculation method to grouted pile in gravel and the principle of choosing grouting parameters, which provides experiences for applying this technique and further studying.