Development of simple and compact in-situ testing system measurement in unsaturated soils

饱和-非饱和土水力特性的原位测量与评价，对于实际、准确地预测天然边坡、路堤、垃圾填埋场和农田等土体中的水分运动至关重要。本文首先提出了一种快速、简便、无损的非饱和砂质土近地表土壤含水量剖面测量方法。利用地面探地雷达（GPR）系统，以电磁波速度测得的土壤介电常数为函数，估算了测区土壤平均含水量。与侵入式土壤湿度传感器相比，探地雷达有几个优点。探地雷达系统提供了一种简单的原位测定土壤含水量的方法，并且是一种完全非侵入式的测量方法。探地雷达可能适合于在大样本量下进行低成本的土壤含水量剖面制图。其次，提出了一种在非饱和土近表面连续测定现场饱和和非饱和导水率的现场试验新方法。在此方法中，我们基于现场和数值实验研究了一种池塘式单环渗透计技术，如圭尔夫压力渗透计（GPI）方法。采用GPI法确定油田饱和水力导电性。采用单位梯度假设下的瞬时剖面法确定了排水过程中非饱和导电性随体积含水量的变化规律。垂直土壤水分剖面采用便携式多深度土壤水分信息采集装置进行测量。该方法的优点是可以通过非常简单的原位渗透试验数据来测量非饱和土的水力导率。通过数值模型验证了该方法的有效性。

It is well noticed that in-situ measurement and evaluation of saturated-unsaturated soil hydraulic properties is essential to practical and accurate prediction of water movement in soil such as natural slope, embankment, landfill and agricultural field.In this research, firstly a fast, simple and nondestructive procedure to measure near-surface soil water content profiles in unsaturated sandy soils is proposed. Surface ground-penetrating radar (GPR) system is employed to estimate the average soil water content in the survey region as a function of the soil dielectric constant measured by electromagnetic wave velocities. GPR has a couple of advantages over the intrusive soil moisture sensors. GPR system offers a simple approach for in-situ determination of soil water content and a completely non-intrusive measurement. GPR may be a suitable for low-cost mapping of soil water content profiles in large sample volume.Secondly, a new field experimental method of determining field-saturated and unsaturated hydraulic conductivity continuously in the near surface of unsaturated soils is proposed. In this method, a ponded single-ring infiltrometer technique, such as the Guelph Pressure Infiltrometer (GPI) method has been investigated based on the field and numerical experiments in our study. The GPI method is performed to determine the field-saturated hydraulic conductivity. The instantaneous profile method with the unit gradient assumption was applied to determine unsaturated hydraulic conductivity as a function of volumetric water content during drainage period. The vertical soil moisture profiles were measured by using a portable device for collecting soil water content information from multiple depths. The advantage of the proposed method is that it allows measurement of hydraulic conductivity of the unsaturated soils by quite simple in-situ permeability test data. The utility of our proposed method is demonstrated by using numerical models.