碎石土土体性状对桩基水平承载能力的影响

EFFECT OF GRAVEL-SOIL CHARACTERS ON LATERAL BEARING CAPACITY OF PILE FOUNDATION

桩基作为一种广泛使用的基础形式,其在如地震荷载、风荷载下的水平承载力确定十分重要。桩基水平承载能力主要由桩身及土体性质控制,而土体性质中密实度和含石量是影响碎石土场地上桩基水平承载能力的主要因素。为明确碎石土场地土性对桩基水平承载能力的影响,在室内开展5组不同土体密实度和含石量下的水平场地单桩水平静载试验,以此模型试验数据计算所得的临界荷载、极限荷载、水平扩散角、计算宽度和水平抗力系数的比例系数m值等为指标评价土体密实度和含石量对桩基水平承载能力的影响。试验结果表明增大密实度和含石量对各指标均有提升效果,但相比之下,密实度对各项指标的提升效果均明显优于含石量。综合考量下,碎石土密实度和含石量的增大均对桩基水平承载力有提升作用,但土体密实度的提升作用更明显。故对水平承载力要求较高的碎石土上桩基工程的选址中,应优先选择密实度较大的场地。

The lateral loading capacity of various foundations are facing different requirements when they are applied to more and more fields.As the widespread usage of foundation forms,pile foundation plays an important role in various engineering.The two kinds of bearing capacity of pile foundation include vertical bearing capacity and lateral bearing capacity.Lateral capacity plays a crucial role in many situations in order to determine the stability under the seismic load and wind load specially.The lateral bearing capacity of pile foundation is mainly affected by pile and soil properties while the compactness and stone content of soil are the major factors to influence the lateral bearing capacity of the pile foundation on the gravel soil.This paper aims to clarify the influence of soil properties from the gravel soils on the lateral bearing capacity of pile foundations.It carries out 5 groups of indoor tests on static lateral loading test of single piles under different soil compactness and stone content.To achieve the expectation of the test,the relationship of piles top displacement and lateral load is recorded.Their curves are plotted for the relationship with different compactness and stone content.Furthermore,critical load and ultimate load are found from these curves.As the load increases,the development of soil fissures surrounding the pile is recorded by taking photos and sketching in the progress of loading and writing explanations.The stress-strain process is divided into three parts according to the curve of piles top displacement and lateral load and the development of soil fissure surrounding the pile.Lateral radial angle is obtained from the soil fissure angle surrounding the pile and is another important index to explain the lateral bearing capacity of pile foundation.According to the principle of horizontal diffusion,the effective calculating width in different soil properties is calculated using the lateral radial angle.Finally,the formulation of effective calculating width which provided by specification is adopted to calculate the proportional coefficient of lateral resistance coefficient-m value.It is proved that when the soil compactness is increased by 20%the critical and ultimate load growths are about 1.5 KN and 1.7 KN respectively,the horizontal diffusion angle growth is about 13°and the m value growth is about 120 MN/m 4.When the soil stone content is increased by 20%critical and ultimate load growths are about 0.6 KN and 0.5 KN,respectively,the horizontal diffusion angle growth is about 3°,the m value growth is about 50 MN/m 4.The experiments show that the increasing of compactness and stone content has an improvement on each index.But by contrast,the effect of compactness on various indexes is obviously better than that of stone content.Under comprehensive consideration,the increasing of compactness and stone content of gravel soil can enhance the lateral bearing capacity of pile foundation,but the effect of soil compactness is more obvious.Therefore,as for the site selection of pile foundation engineering on gravel soil which requires higher horizontal bearing capacity,the site with higher compactness should be preferentially selected.