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

本文首先提出了一种快速、简便、无损的非饱和桑迪近地表含水率剖面测量方法，并对该方法进行了理论分析和实验研究。采用地面探地雷达（GPR）系统，以电磁波速度测量的土壤介电常数的函数来估计调查区域的平均土壤含水量。与侵入式土壤湿度传感器相比，探地雷达具有几个优点。探地雷达系统提供了一种简单的方法，原位测定土壤含水量和一个完全非侵入性的测量。探地雷达可用于大样本量、低成本的土壤含水率剖面制图。其次，提出了一种新的连续测定非饱和土壤近地表饱和和非饱和导水率的野外实验方法。在该方法中，一个积水单环入渗仪技术，如圭尔夫压力入渗仪（GPI）方法已被研究的基础上，在我们的研究中的现场和数值试验。GPI方法用于确定现场饱和导水率。采用瞬时剖面法和单位梯度假设，确定了排水期非饱和导水率随体积含水量的变化关系。利用便携式多深度土壤水分信息采集装置，测定了土壤水分垂直剖面。该方法的优点是，它允许测量的非饱和土的渗透系数相当简单的原位渗透试验数据。我们所提出的方法的效用是通过使用数值模型证明。

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.