Development and performance evaluation of a soft-contact earth pressure transducer for geotechnical centrifuge modeling
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摘要: 微型土压计是岩土离心模型试验的重要测量技术之一。为解决刚性土压计测量中拱效应、尺寸效应、厚径比等经典误差问题及提升频响速率和精度，尝试开发了一种全新软接触式微型土压计ESP-Ⅱ，介绍了其技术创新和设计方法。以两种国际代表性土压计为参考，设计开展一系列离心模型试验，对其感应精度、速率和适用性进行评价。主要结论：①逐级加载离心加速度5g~50g试验下，各深度ESP-Ⅱ和两种参考传感器测试结果与理论值的平均误差分别为5.16%，6.70%，4.85%，三者沿深度拟合K0优度系数R2均≥0.9893。②脉冲荷载试验中ESP-Ⅱ最大响应时间约7.8 ms，略优于两种参考传感器，具有良好的频响速率。③不同幅值正弦、地震等动荷载试验下，3种传感器测得土压力均呈一致增量趋势，K0约由0.43~0.45增至0.51~0.56，与既有规律认识吻合。④离心机下降卸荷过程中，ESP-Ⅱ测得时程表现良好连续性和光滑性，反映软接触式设计有利于保障土体与传感器良好接触和稳定响应。研究成果，初步证明了软接触式土压计适应于静、动力离心试验需求，具有重要价值与应用前景。Abstract: The miniature earth pressure transducer is one of the key testing tools in geotechnical centrifuge modeling. Aiming at solving the classical problems such as arching effects, size effects and thickness-diameter ratio in the measurement of rigid transducers, and improving the frequency response rate and induction accuracy, a soft-contact pressure transducer ESP-Ⅱ is developed, and its innovations and design methods are introduced. Taking two internationally representative earth pressure transducers as reference, a series of centrifugal model tests are designed and carried out to evaluate its accuracy, frequency response and applicability. The main conclusions are as follows: (1) In the static centrifugal acceleration tests spinning up from 5g to 50g, the difference between the theoretical values and the test results of ESP-Ⅱ and the two reference transducers at each depth is small, and the average deviations are 5.16%, 6.70% and 4.85%, respectively. The coefficient R2 of the three curves K0 fitted along the depth is≥0.9893. (2) In the pulse load tests, the maximum response time of ESP-Ⅱ is about 7.8 ms, which is slightly better than that of the two reference transducers and has a satisfactory frequency response. (3) In the dynamic load tests of sine and seismic with different amplitudes, the incremental trend of earth pressure measured by the three transducers is basically consistent. The variation range of K0 increases from 0.43~0.45 before the seismic to 0.51~0.56 after the seismic, which is consistent with the existing theory. (4) At the decelerating stage of the centrifuge, the good continuity and smoothness of the time history measured by the ESP-Ⅱ, which reflects the soft-contact design, is conducive to ensuring good contact and stable response between the soil and the transducer. The research results have preliminarily proved that the developed soft-contact transducer ESP-Ⅱ satisfies the requirements of static and dynamic centrifugal tests, with significant application value and immense potential.
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图 1 ESP-Ⅱ微型土压计设计方案及3种传感器实物
Figure 1. Structural design of ESP-Ⅱ miniature transducer and photos of three types of transducers
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图 2 调配与选取最优刚度匹配软接触材料
Figure 2. Reconciliation and test soft-contact materials with different elastic moduli
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图 3 凹、凸、平不同接触面形态设计对比
Figure 3. Design contact surface shapes of concave, convex and plane
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图 8 离心机加速度阶段3种土压计响应测试结果
Figure 8. Static centrifugal test results of three types of earth pressure transducers at celebration stage of centrifuge
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图 9 离心机加载阶段侧向土压力与理论K0分布
Figure 9. Profile of lateral earth pressure and theoretical K0 at celebration stage of centrifuge
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图 10 不同离心力下各组土压计实测侧向土压力变化
Figure 10. Measured values of three types of earth pressure transducers at different centrifugal accelerations
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图 11 脉冲波荷载下土压计动力离心试验结果
Figure 11. Dynamic centrifugal test results of three types of earth pressure transducers under pulse wave
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图 12 连续动力荷载下土压计测量结果
Figure 12. Dynamic centrifugal test results of earth pressure transducers under different seismic amplitudes
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图 13 不同动荷载下侧向土压力分布
Figure 13. Profile of lateral earth pressure under different seismic loads
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图 14 离心力逐级下降阶段3种土压计响应结果
Figure 14. Test results of three types of earth pressure transducers at decelerating stage of centrifuge
表 1 ESP-Ⅱ与国际通用土压计的主要设计参数及材料
Table 1 Main design parameters and materials of three types of earth pressure transducers
型号 量程/kPa 感应元类型 壳体/mm 线缆/mm 厚径比dh 接触面形式 信号类型 ESP-Ⅱ 500 压敏硅膜片 ϕ 10.5 ϕ 1.6 0.47 柔性 电压 PDA 500 电阻应变片 ϕ 7.6 ϕ 1.6 0.21 刚性 应变 EPL-D1 500 电阻应变片 ϕ 5.0 ϕ 1.5 0.32 刚性 电压 
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表 2 静力离心试验3种土压计实测土压力
Table 2 Earth pressures measured of three types of earth pressure transducers by static centrifuge spinning up 5g to 50g
离心加速度/g 土层深度/m 传感器位置/m 土压计实测值/kPa ESP-Ⅱ(IEM) PDA(TML) EPL-D1(Measurement) 5 2.0 0.75 3.41 4.89 4.33 1.25 7.01 5.81 7.66 1.75 9.97 7.48 9.23 10 4.0 1.50 7.39 9.69 9.41 2.50 14.59 13.38 16.25 3.50 22.15 17.08 21.41 15 6.0 2.25 12.46 14.40 13.11 3.75 22.89 21.23 24.74 5.25 33.69 27.32 30.28 20 8.0 3.00 16.80 19.20 18.00 5.00 30.74 28.89 32.86 7.00 45.51 36.92 40.06 30 12.0 4.50 25.48 29.08 25.85 7.50 44.31 45.88 49.20 10.50 69.51 60.65 65.54 40 16.0 6.00 36.18 39.60 36.08 10.00 62.49 63.41 66.46 14.00 89.81 83.54 87.41 50 20.0 7.50 47.82 49.66 51.51 12.50 78.28 80.31 82.43 17.50 106.89 107.35 109.85
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