摘要
目前大直径超长桩的可打入性分析的准确性是打桩施工顺利进行的重要保障,打桩过程中土阻力预测是其中的关键一环。近几年高应变动测技术迅速发展,凭借其突出优势成为动力沉桩分析的新方法。结合高应变动测试验采用CAPWAP软件对打桩过程中土阻力进行分析,被广泛应用于海洋桩基监测和承载力评估中。CAPWAP程序中涉及的土阻尼系数Js和Jt对承载力计算影响非常大,是非常重要的参数,阻尼系数的取值直接影响承载力计算的准确性。为得到更准确的阻尼系数,对东海某工程2根桩进行全程高应变动测试验,并利用CAPWAP软件对其中一根桩的实验结果进行分析,对桩周土体阻尼系数做了研究,认为同打桩过程中的桩侧阻尼系数并非一成不变的,而是随着打桩的进行存在减小的趋势。
The accuracy of drivability analysis for piles with large diameters is very important for pile driving safely.The prediction of soil resistance to driving（SRD）is the focus of this analysis.Numerous models have been developed to predict soil resistance.With many outstanding advantages,the technology of high-strain testing is the basis for a new advanced method for pile-driving analysis.The Case Pile Wave Analysis Program（CAPWAP）method is generally used to analyze dynamic tests data to obtain the SRD.CAPWAP is based on one-dimensional wave theory,which is widely used in pile foundation monitoring and bearing capacity evaluation in ocean engineering.Using CAPWAP to analyze the data from dynamic testing,the SRD can be determined during the entire pile installation procedure.When using CAPWAP,soil factors and pile parameters such as damping,quake force,and wave velocity should be determined.Among the parameters,the soil damping coefficient of friction Jsand top of pile Jt,have the greatest influence on pile bearing capacity.Soil damping coefficients are the most important parameters of soil dynamics.Various models have proposed distinct Jsand Jt,and each soil type has a specific damping value.For example,the Smith model proposed values of 0.16 and 0.48 for Jsand Jt,respectively,and the Case model recommended Jsvalues of 0.15 for cohesive soil and 0.65 for cohesionless soil;Jtwas 0.5regardless of soil type.Many models widely use the value of 2.54 mm for quakes.Although many scholars give different experience values,the Case damping coefficients are widely adopted in most cases.Engineering applications reveal that various soil parameter values strongly influence the SRD;therefore,the study of soil parameter values is meaningful.To obtain more accurate damping parameters and to improve the reliability of CAPWAP,this study examines the results of pile dynamic testing of an engineering application in the East China Sea.During pile installation,the pile is struck up to 1868 times to penetrate the design depth,with each blow containing a set of corresponding force and velocity curve.In this study,we analyze approximately 200 curves by CAPWAP to obtain a set of soil parameters for each layer.To obtain the changes in Jsand Jtwith depth,numerous data are analyzed.First,a study is conducted to determine Jsand Jt with various penetration depths.The results show that the soil damping coefficients increasingly decay rather than remain constant during piling and change with penetration depth.Therefore,when using CAPWAP to predict the soil resistance to driving,using a constant for Jsor Jtduring the entire pile installation is not reasonable and will result in error.To further study the changes in soil damping coefficients during pile installation,the relationship of soil damping coefficients with blows is examined.It is determined that the change trend of blows is in contrast to that of the damping coefficient.Finally,this study analyzes the change trend of soil damping coefficients with depth.During the piling procedure,the factor value is shown to steadily decrease in a manner similar to a linear gradient.
出处
《地震工程学报》
CSCD
北大核心
2014年第4期946-951,共6页
China Earthquake Engineering Journal
关键词
土阻尼系数
CASE阻尼
高应变动测
CAPWAP软件
波动方程
土阻力
桩基
soil damping coefficient
CASE soil damping
high strain testing
CAPWAP
wave equation
soil resistance to driving（SRD）
pile foundation
