由O-cell试桩结果确定整桩的性能

提出了一个根据O-cell试桩结果确定整桩性能的途径,包括基本方法、步骤及必须的资料。以某公路大桥的O-cell试桩为例,采用本文所提出的途径确定出了桩阻力参数、相应整桩的荷载沉降曲线及极限承载力。验证了桩侧阻力与接触面两侧切向位移差之间关系可以用双曲线表示。将按本文提出的方法和现有其他四种方法确定的整桩荷载沉降曲线做了比较,并对各种确定整桩荷载沉降曲线方法的可靠性和适用性做了评价。此外,将按本文给出的整桩荷载沉降曲线和按流行公式确定的整桩极限承载力做了比较,指出了流行公式低估了整桩极限承载力,并对流行公式提出了一个修改建议。强调了,只有按某种有根据的方法确定出完整的整桩荷载沉降曲线,才能由O-cell试桩结果可靠地确定出整桩的极限承载力。     

深埋泥炭质粘土的力学性能

为研究深埋的泥炭质粘土的静力和动力性能进行了静力和动力试验,进行了静力和动力试验.通过静力试验,验证了双曲线应力应变关系及邓肯—张模型也适用于泥炭质粘土,测定了邓肯—张模型参数,并发现参数k、c、随的埋深增加而增大.动力试验结果验证了Hardin和Drnevich提出的动力学模型也适用于泥炭质粘土,測定了相应的模型参数,发现参数kG.d随的埋深增加而增大.确定了在原位条件下的Gd/Gd..max-r及λ/λmax-r关系线,并与Seed建议的一般粘性土平均的关系线做了比较.发现的模量比Gd/Gd..max随剪应变幅值r增加衰减地比较慢,线性阶段可延续到剪应变幅值达到10-4.相应地,泥炭质粘土的λ/λmax-r关系线也明显地不同于Seed建议的粘性土平均的λ/λmax-r关系线.     

Simulation analysis for O-cell test of pile and the interaction of upper pile and lower pile

In this paper,the soil-pile system of O-cell test of pile is simplified as an axi-symmetric problem.By using aggregation of quadrilateral isoparametric elements to simulate pile and soil,setting Goodman’s elements between pile and soils,a method of numerical simulation analysis on O-cell test of pile is presented with the consideration of nonlinear mechanical behavior of soils and pile-soil interface.The method is applied to the analysis of a case of O-cell test of pile.The load-displacement curves and axial force curves of upper pile and lower pile obtained from the O-cell test of pile are fitted,and parameters of the mechanical model of soils and interface are determined.Analysis results validate that the numerical simulation analysis method put forward in this paper is applicable.Furthermore,the interaction and influence of upper pile and lower pile in the O-cell test are also studied with the method.The result shows that if load box is located in a soil layer with fine mechanical behavior,the interaction of upper pile and lower pile in O-cell test can be ignored generally.     

土动模量的退化和阻尼比变化

针对双曲线关系不能很好地拟合土动模量随动力作用水平的退化,及Hard in和D rnevich的确定阻尼比的公式低估了动力作用水平低于一定值时的阻尼比的问题,基于3种黏性土动模量的试验结果,提出了一个能很好拟合动模量退化的数学关系,式中所包括的参数少且容易确定.研究了固结压力对动模量退化的不可忽视的影响,提出了一个确定阻尼比的改进公式.上述成果可以合理地确定动力分析中土的动模量和阻尼比,提高分析结果的可信性.