离心模型试验中微型土压力盒土压力测定

Determination of earth pressure by miniature earth pressure cell in centrifugal model test

土压力作为离心模型试验中重要的测试参数,受土压力盒的性能、离心机数据采集系统稳定性及外部环境等诸多因素的影响,准确地测量土压力较为困难。土压力盒作为土压力测试元件,其性能对土压力测量准确性有直接影响。为获得较为准确的土压力测试数据,结合离心机数据采集系统,选择两种常见的电阻应变式土压力盒。通过标定试验得出两种土压力盒砂标系数均小于出厂标定系数,Ⅰ型偏小64.75%,Ⅱ型偏小18.77%,Ⅱ型土压力盒与出厂数据的重合度比Ⅰ型好;在研究墙高10～30m类扶壁式挡墙侧向土压力分布的离心模型试验中,与Ⅱ型土压力盒相比,Ⅰ型存在按出厂系数测得数据失真、灵敏度低和稳定性差的缺点。标定试验和离心试验结果表明,接入自行组建的数据采集系统的Ⅱ型土压力盒比接入静态应变数据采集系统的Ⅰ型土压力盒性能更佳。

Earth pressure is an important test parameter in centrifugal model experiment, it can be affected by many factors such as the performance of the earth pressure cell, the stability of the centrifuge data acquisition system and the external environment, so accurate measurement of earth pressure is hard to obtain. As a component of earth pressure measurement, the performance of earth pressure cell can directly affect the accuracy of earth pressure measurement. To get more accurate test data, two common resistance strain type earth pressure cells are selected to test using the centrifuge data acquisition system. The calibration test shows that two cells’ calibration coefficients of sand are smaller than the factory calibration coefficients. The calibration coefficients of sand for the type Ⅰ are 64.75% lower than the factory calibration coefficients, and that of type Ⅱ are 18.77% lower. The coincidence degree between type Ⅱ earth pressure cell and factory data is better than that of type Ⅰ earth pressure cell. In a centrifugal model test for measuring the lateral earth pressure distribution of counterfort retaining wall with wall height of 10-30 m, type Ⅰ earth pressure cell has some shortcomings, such as data distortion measured by factory calibration coefficients, poor stability and low sensitivity, compared with the type Ⅱ cell. The results of calibration test and centrifugal test show that type Ⅱ cell with self established data acquisition system has better performance than type Ⅰ with static strain data acquisition system.