Flexible Wall Soil Permeameter for Gas Transport Measurement
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Solution Overview
Problem
Existing rigid wall devices for measuring gas permeability and diffusion coefficients in unsaturated soils suffer from preferential side-wall flow, inability to simulate field stress conditions, and inability to quantify volume changes due to wetting and drying cycles, leading to inaccurate measurements.
Innovation Solution
A flexible wall device with a gas washing system, confining pressure-volume change system, and drying-wetting cycle control system, which includes a high-purity nitrogen cylinder, humidity controller, and pressure regulating valves, allows for precise measurement of gas permeability and diffusion coefficients by minimizing side-wall flow and simulating field conditions through controlled humidity and pressure changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a rigid wall permeameter is used to measure gas permeability coefficient and gas diffusion coefficient, then the measurement can be performed with a simple device structure, but preferential side-wall flow of gases occurs between the sample and rigid wall, leading to overestimation of gas transport parameters
Solution Approach 1:
The patent replaces the rigid wall structure with a flexible membrane (latex film) that conforms to the sample surface, eliminating gaps between the sample and wall. This flexible membrane prevents preferential side-wall flow of gases while maintaining device simplicity, thus resolving the contradiction between device complexity and measurement precision.
2Ease of manufacture
If a rigid wall permeameter is used, then the device is easy to manufacture, but the device cannot quantify volume change of soils under drying and wetting cycles
Solution Approach 1:
The patent introduces a flexible membrane instead of a rigid wall, enabling the device to dynamically adapt to volume changes of the soil sample during drying and wetting cycles. The membrane flexes with sample expansion and contraction, allowing volume change quantification while maintaining ease of manufacture through the use of simple flexible materials.
3Device complexity
If a rigid wall permeameter is used, then the device structure is simple, but the device cannot avoid preferential sidewall flow of gases
Solution Approach 1:
The flexible membrane creates intimate contact with the sample surface, eliminating the annular gap that causes preferential sidewall flow. This simple flexible structure ensures reliable gas flow measurement through the sample by forcing all gas to pass through the sample rather than bypassing it along the wall interface.
4Reliability
If separate devices are used to measure gas permeability coefficient and gas diffusion coefficient, then each measurement can be performed with dedicated equipment, but sample loading and unloading in different instruments causes sample breakage and affects measurement results
Solution Approach 1:
The patent designs a single permeameter device that can perform both gas permeability coefficient and gas diffusion coefficient measurements. The flexible membrane structure and controlled atmosphere system enable the same device to conduct different types of gas transport measurements on the same soil sample without requiring sample removal or reloading, thus preventing sample breakage and improving measurement reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The flexible wall device accurately measures gas permeability and diffusion coefficients while accounting for volume changes caused by wetting and drying cycles, enhancing measurement accuracy and range, and allowing for simultaneous measurement of these parameters across different moisture contents.
Implementation Method 1
The gas migration of unsaturated soil occurs through two main transport mechanisms: convection and diffusion, where the convection is influenced by the gas permeability coefficient (ka) and gas pressure gradient of the soil
Implementation Method 2
the diffusion is influenced by the gas diffusion coefficient (Dp) and gas concentration gradient in the soil
Data Source
AI summary
A flexible wall device and method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil includes a gas washing device, a confining pressure-volume change system, a drying-wetting cycle control system and a gas measuring device. The drying-wetting cycle control system includes a humidity controller and valves. The gas measuring device includes a top lid, a cylindrical wall, a base, an upper chamber and a lower chamber. The top lid, the cylindrical wall and the base are connected by bolts and nuts, and the base has four passages, which are respectively connected to the gas washing device, the confining pressure-volume change system, the drying-wetting cycle control system and the gas measuring device, between the base and top lid are sequentially arranged from bottom to top as the lower chamber, lower perforated plate, lower permeable stone, sample, upper permeable stone, upper perforated plate, upper chamber, and control rod.