Flexible Wall Permeameter Research Articles

Harnessing Microbial-Induced Calcite Precipitation for Sustainable Seepage Control in Cohesionless Soil Channels

Seepage control in unlined channels is critical for efficient water resource management, as excessive water loss through channel beds and walls leads to inefficiencies. Microbial-induced calcite precipitation (MICP) offers a promising solution to enhance soil stability and reduce seepage in cohesionless soils. This study investigates the application of MICP using Bacillus subtilis to mitigate water leakage in sandy soils through controlled experiments. A bacterial solution was introduced into soil samples, followed by urea and calcium chloride solutions, facilitating calcite precipitation and bioclogging. pH monitoring and calcium carbonate quantification confirmed the process. Results showed a 26% increase in calcium carbonate content in treated soil, significantly reducing permeability from 6.8 × 10−3 to 1.11 × 10−3 cm/s, as measured by a flexible wall permeameter. Soil strength increased from 234 to 1407 kPa, determined by triaxial compression tests. Validation was achieved using XRD, EDS, and SEM analyses. An interdisciplinary co-occurrence network graph from Scopus data highlighted key concepts like calcium carbonate, calcite precipitation, B. subtilis, bioclogging, and soil stabilization. MICP aligns with several UN Sustainable Development Goals (SDGs), notably SDG 6 by enhancing water retention, SDG 9 by promoting sustainable construction, and SDG 13 by improving soil stability against climate-related hazards. Thus, MICP is a sustainable and effective method for constructing impermeable channels, offering significant water management benefits.

Evaluation of Water and Air Fluxes in Mixtures of Soil and Organic Compound for Oxidative Covering Layers

Objective: The aim of this study is to assess the air and water permeability of soil mixtures with organic compost in different proportions in order to determine the gas and liquid fluxes for use in landfill cover layers. Method: The methodology adopted for this study includes laboratory tests to characterize the materials and the use of the flexible wall permeameter model Tri-flex 2 from Soil Test – ELE to determine the air and water permeability of the materials. Mixtures in proportions of 2:1 (soil:compost) and 1:1 (soil:compost) were used as materials for the oxidative covering layer. Results and Discussion: Based on the results obtained, it is possible to conclude that the mixtures present permeabilities to air and water in accordance with the standards indicated by USEPA (2003) for covering layers in sanitary landfills, thus ensuring that there is no excess percolation of water from rain, as well as the emission of polluting gases into the atmosphere. Research Implications: The studied material is potentially suitable for use in oxidative cover layers for sanitary landfills, proving to be a viable alternative for implementation in smaller municipalities with less purchasing power, reducing the need to use clay materials, without detriment to the operational efficiency of the landfill. Originality/Value: One of the difficulties faced by municipalities in using sanitary landfills is the search for suitable materials, especially in municipalities with lower purchasing power or located in arid regions, where the use of conventional layers presents problems, with drying out and opening of fissures. The relevance and value of this research are evidenced by the feasibility of combining clay soils with organic compost to create oxidative cover layers, reducing the pollutant load of organic waste.

Real-time ultrasonic water level IoT sensor for in-situ soil permeability testing

Soil permeability tests require a time series of water level measurements to determine system losses, including both infiltration and evaporation. Laboratory measurements of flow are standardised by international regulations such as ASTM International, ISO or UNE, but field measurements are not as well described and in some cases may require definition and specification of test conditions. This is the case for geosynthetic clay liner (GCL) products, where permeability is assessed by a laboratory measurement using a flexible wall permeameter as defined in standard test method D 5887-04. This method is not able to evaluate the performance of such products in the field and therefore cannot guarantee their ability to be used for the repair of landfill liner overlays. For this reason, we have defined a field test in a confined steel ring and developed a real-time ultrasonic IoT device to evaluate water losses over a period of time. The test method was applied in Mallorca (Spain) and as a result the quality of a landfill cover repair solution was evaluated, the corresponding civil works were carried out and the basis for future field measurements of soil permeability tests on different materials and conditions was established.

An insight into laboratory column experiments for microplastic transport in soil

Plastic litter, most of which is landfilled or improperly disposed to aquatic and terrestrial environments, is a global environmental concern. Large-sized plastics can fragment into smaller pieces due to abrasion or weathering effects generating microplastics (MPs) which are tiny plastic debris smaller than 5 mm. In the aquatic environment, particularly oceans, MPs have been well documented in terms of their occurrence and toxicity. Soils have been shown to be an important sink of MPs, but the latter's fate and transport in the subsurface are not well understood. Laboratory studies have so far mostly employed rigid-wall columns to investigate MP transport through porous media, with a vast majority focusing on glass beads and predominantly sandy soils. Much less knowledge is available on MP transport in clay soils and minerals where transport mechanisms are much slower and the potential for chemical reactivity higher. There is hence a need for establishing experimental protocols for conducting such experiments. The paper presents preliminary results for an investigation assessing whether flexible wall permeameters (FWP) are suitable for the study of the transport of MPs in clayey soils. Key advantages of FWP are that they are widely available and commonly used and that they allow the control of effective stress in the sample. Two key questions addressed in this paper are whether the instruments themselves act as sink for MPs or as source of material that may interfere with the measurement of MPs in the effluent.

Saturated permeability and water retention capacity in biochar-methanotrophs-clay for new landfill cover system

A new landfill cover system, biochar-methanotrophs-clay (BMC) cover is recommended for reducing methane emissions at landfills. It also contributes to decreasing soil permeability and improving soil water retention in a long time, due to highly porous structure of biochar and the growth metabolism of methanotrophs. To determine the effects of biochar content, oxidation aging times and methane-filled days on hydraulic properties, a total of 60 groups of experiments were conducted. The saturated hydraulic conductivity (ksat) was obtained by flexible wall permeameter with controllable hydraulic head pressure. The results showed that the ksat of BMC increased with increasing biochar content and oxidation aging times, while decreased with adding methane-filled days. The soil-water characteristic curves (SWCCs) were obtained with soil suction measured by the filter paper method. The results indicated the water retention capacity of MBC reduced with increasing oxidation aging times but increased with adding methane-filled days. Detected by mercury intrusion porosimetry (MIP), fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), the differences displayed the changes of pore structures and extracellular polymeric substances (EPS). The oxidation aging of biochar increased the volume of pores, resulting in the increased ksat and the decreased water retention capacity. However, the growing of methanotrophs decreased the volume of pores, resulting in the ksat decreased and the water retention capacity increased due to EPS. No matter how many times the oxidation aging process was experienced, the BMC with longer methane-filled days exhibited relatively lower ksat and better water retention capacity. This implied a more stable barrier capacity to reduce water infiltration in the long term. By combing a series of macro and micro experiments, this paper provides theoretical guidance for the application of biochar-methanotroph-clay mixture to landfill covers.

Influence of initial compaction and confining pressure on the hydraulic conductivity of compacted iron ore tailings

The hydraulic conductivity of iron tailings is an important factor affecting the stability of tailings storage facilities. Stacking compacted filtered ore tailings is a promising alternative for safer tailings disposal. These tailings storage facilities’ internal drainage systems must be designed appropriately to avoid excessive seepage pressure, saturation, and slope failure. In this context, the factors that affect hydraulic conductivity must be adequately evaluated. Therefore, the hydraulic conductivity behavior of compacted iron ore tailings still needs to be investigated. In addition, the effect of high confining pressure on hydraulic conductivity needs to be evaluated. This study investigates the impact of the initial compaction and the confining pressure on hydraulic conductivity. For this, the flexible wall permeameter tests were carried out on filtered ore tailings compacted in three degrees of compaction: 77, 94, and 101% of optimum dry density as determined by the standard Proctor method. These specimens were saturated and then consolidated with different confining pressure. It is possible to affirm that the increased confining pressure decreases the hydraulic conductivity. The hydraulic conductivity decreases by less than one order of magnitude, regardless of the initial compaction. Moreover, the data suggest that hydraulic conductivity’s decay rate depends on initial compaction—the hydraulic conductivity of the loose specimen decays at a greater rate than that of the dense specimens. However, the reductions of the void ratio under the confining pressure of 1600 kPa and 2200 kPa were not enough to decrease the hydraulic conductivity. Thus, under high-stress confining, the hydraulic conductivity becomes practically constant.

Assessment of a new rigid wall permeameter for the slurry like barrier materials: zeolite example

Areas vulnerable to catastrophic disasters such as hurricane, landslide and earthquake require ready and sustainable solutions for the post-pollution scenarios. Clinoptilolite type zeolite re- sources of Türkiye can serve economical and sustainable solutions as a quick response. While the studies on compacted zeolite-bentonite mixture at optimum water content for the landfill liners applications or dry zeolite-sand mixtures in permeable reactive barrier (PRB)s are com- mon, the slurry form of zeolite emplacement at subsurface reactive barriers has not received an attention by the researchers. In this context, this experimental study presents the prelimi- nary findings on one-dimensional consolidation and hydraulic conductivity tests performed on crushed zeolite samples S1 and S2 with fine contents of 33 and 84%, respectively. The results indicate that S2 has a higher compression index than S1, without a significant change in swelling index attributed to less than 4% clay contents. A self-designed rigid wall type per- meameter was used to study on reconstituted slurry like materials under the benefit of back pressure saturation without the consolidation during testing that encountered in flexible wall permeameter. Falling head – rising tail water procedure was adopted under the back pressure in between 200 and 700 kN/m2. S2 samples reconstituted under 25, 50, 100 and 200 kN/m2 show a gradual decrease in kv from 3×10-8 to 2×10-9 m/s. Previous observations on the sample of S1 revealed 8 times higher kv values under the same σv'. Since the fine content of zeolite limits kv, the proposed permeameter will be beneficial to determine the proper grain size dis- tribution of fill materials considering the barrier height and in-situ stress conditions before the environmental studies with leachate.

Study on the relationship between permeability coefficient and porosity, the confining and osmotic pressure of attapulgite-modified loess

This study investigated attapulgite-modified loess as an efficient and cost-effective method for creating an impermeable liner for landfills in regions with scarce clay resources. Laboratory permeability tests were conducted using a flexible wall permeameter to determine the permeability of compacted loess and attapulgite mixtures under varying osmotic conditions. The relationship between the permeability coefficient, attapulgite dosage, radial pressure, and osmotic pressure was analyzed. Nuclear magnetic resonance and scanning electron microscopy were also used to observe the microstructure of the modified loess. The results showed that attapulgite dosage significantly reduced the permeability coefficient, but the effect became limited when the content surpassed 10%. The decrease of the permeability coefficient of the modified loess is mainly due to the filling of pores between the loess by attapulgite, which makes the pore size and throat size of the modified loess smaller. The modified loess displayed a sheet structure that contributed to an increased permeability coefficient due to increased radial pressure. This study provides valuable insights into using attapulgite-modified loess as a material for landfill lining in regions with scarce clay resources.

Experimental study on impermeability of Loess liner mixed with bentonite-HDTMA

Permeability tests are performed by using the flexible wall permeameter to study the influence of bentonite-HDTMA (hexadecyl trimethyl ammonium bromide) on the permeability performance of Loess as a lining material in the solid waste landfill. Results show, the impermeability of compacted Loess in the middle and lower reaches of the Yellow River in China does not meet the standard requirement as the landfill liner. The permeability of Loess mixed with more than 10% bentonite ratio is less than 1.0 × 10−7 cm·s−1. The permeability of Loess increases slightly after mixing a small amount of HDTMA. The impermeability of Loess mixed with some bentonite-HDTMA ratio still meet the standard requirement. The HDTMA may destroy the soil aggregate structure and increase the soil permeate channel. The SEMs show that the bentonite clay particle can fill the pores between Loess coarse particles and improve the impermeability performance of the material. The digital photos show that HDTMA can effectively resist the development of soil macro-cracks induced by wetting–drying cycles, better for liner to maintain good impermeability. On this basis, the relationship between the hydraulic conductivity of bentonite-HDTMA modified Loess and dry density is constructed. From this study, Loess can be used as a lining material for landfills, when mixed with bentonite/HDTMA at ratios of 10%/0% or 14%/2%.

Performances of the Soil–Bentonite Cutoff Wall Composited with Geosynthetic Clay Liners: Large-Scale Model Tests and Numerical Simulations

The geosynthetic clay liner (GCL) overlap plays a key role in maintaining hydraulic performance of the barrier systems, e.g., the bottom liner and cover systems. However, its influences on the behavior of the vertical barrier have been rarely investigated. This paper aims to address this issue using the large-scale model test and 3-dimensional finite element (FE) modeling. In the model test, the GCL overlap at the width of 500 mm was tested under a constant hydraulic head of 1 m and confining stress ranging from 10 to 150 kPa using a newly developed large-scale apparatus. Compared with the flexible wall permeameter, this apparatus could guarantee full field-scale GCL overlap to be tested. Results showed that the effective hydraulic conductivity of the GCL overlap decreased from 10−8 to 10−9 cm/s as the confining stress increased from 10 to 150 kPa. The addition of supplemental bentonite paste in between the overlap with a water-to-bentonite ratio of 19:1 contributed to reducing the effective hydraulic conductivity by 60% compared with that for a GCL overlap without bentonite paste. The breakthrough time for the soil-bentonite (SB) cutoff wall composited with GCLs was 64% longer in comparison with that for the single SB wall. Additionally, the breakthrough after 50 years is made for the entire depth of the single SB wall while at the depth no more than 0.9 m for the composite wall with bentonite paste at the GCL overlap. With consideration that the depth of the groundwater table is generally greater than 1 m, the GCL–SB composite cutoff wall will exhibit a good performance in containing groundwater contaminants in the field, especially when applying bentonite paste at the GCL overlap.

Porous stones in permeability measurement: drawbacks and solution

Porous stones are commonly used in geotechnical laboratory testing to provide solid support at the two ends of the tested specimen. Although porous stones can have several advantages, they can induce a hydraulic impedance that might alter the flowrate results. Numerous suggestions and recommendations were issued to avoid some of the problems encountered when using porous stones, such as clogging and stones' low permeability coefficient ( Kp). However, it is proven in this technical note that the existence of a soil–porous stones interaction prevents the elimination of porous stones' influence, leading to unreliable permeability results. A practical solution based on manufacturing unique porous stones (MS) is suggested in an attempt to eliminate such an influence. The porous stones' influence is highlighted by running excess pore pressure dissipation tests under triaxial conditions with calibrated beads. The results show a soil–porous stones interaction and a flowrate increase up to 700% due to MS. This interaction is addressed through permeability measurements of three soil types in a flexible-wall permeameter using standard porous stones (SS) and the newly manufactured stones (MS). At least one order of magnitude of difference in the soil permeability measurement and a decrease in the dissipation test time are observed with MS. This technical note also validates the limitation of the superposition approach for correcting the soil's permeability ( Ksoil). It is shown that porous stones can induce a signature directly related to the soil type and applied pressure.

Saturated hydraulic conductivity of compacted steel slag-bentonite mixtures——A potential hydraulic barrier material of landfill cover

The feasibility of using steel slag and bentonite mixtures to construct the hydraulic barrier of a landfill cover was explored in the present study. Fine-grained steel slag (SS; particle diameter < 1 mm) and sodium-activated calcium bentonite (SACB) were used to prepare compacted specimens, and the saturated hydraulic conductivity (ks) was measured using a flexible-wall permeameter. Influential factors including SACB content (BC), SS gradation, water-washing treatment of SS and compaction water content (ωcomp) were investigated. The hydraulic conductivity results were interpreted in microscopic scale through mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). It was found that when BC was below 10%, the ks value of the specimens prepared with well graded SS was about one order of magnitude lower than that of the specimens prepared with poorly graded SS. This was due to less macropores caused by better SS gradation. Yet, the effects of SS gradation on ks diminished as BC further increased to 15%, suggesting the dominant role of BC on ks at high BC. Water-washing treatment of SS helped reduce ks significantly to 1.2 × 10−10 m/s at BC of 10%, owing to less multivalent cations and hence lower osmotic swelling reduction caused by cations. Controlling ωcomp 1–2% wetter than the optimum water content (ωopt) also helped reduce ks significantly, owing to the reduction of macropores. Accordingly, it is suggested to use well-graded SS mixed with 10% SACB and then compact at ωcomp slightly wetter than ωopt to the degree of compaction greater than 90% in engineering practice.

Air and hydraulic flow characteristics of polymer amended bentonite based unsaturated GCLs

Geosynthetic clay liners (GCLs) are used in landfill applications because of their high deformation resistance and excellent self-healing ability. In the present study, air and hydraulic flow characteristics of natural bentonite based GCL (GCL-N) and polymer amended bentonite based GCL (GCL-A) were assessed using air permeability and hydraulic conductivity measurements. The airflow characteristics of GCLs were studied at various apparent degrees of saturation (Sa) and corresponding suction using a custom-designed air permeability test setup. The effect of desiccation on the airflow characteristics of GCL-A was also examined. Further, hydraulic flow characteristics of virgin and desiccated-rehydrated GCLs were assessed using a flexible wall permeameter. The water absorption capacity of GCL-A is relatively higher than GCL-N, irrespective of the stress state. For any chosen Sa, air permeability of GCL-A is lower than GCL-N. Moreover, with the decrease in the suction from 2500 kPa to 1000 kPa, the air permeability of virgin GCL-A has reduced from 9 × 10−12 m2 to 3.57 × 10−16 m2 while the desiccated-rehydrated GCL-A has reduced from 8.86 × 10−11 m2 to 1.9 × 10−13 m2. The hydraulic conductivity of GCL-A is two orders of magnitude less than GCL-N, which shows the better performance of GCL made with amended bentonite.

Predicting Hydraulic Conductivity for Flexible Wall Conditions Using Rigid Wall Permeameter

The hydraulic conductivity is known as the soil properties that mostly vary over an order of magnitude. There are many laboratory test methods to determine the hydraulic conductivity of the soil. Each test has its own merits, drawbacks and limitations. One of these methods is the measurement using a rigid wall permeameter (RWP), which is a common practice to obtain the fluid transmissibility characteristics of the soil matrix. This type of permeameter has the advantages of low cost, simplicity of test equipment, and adaptability to many different types of permeant liquids. Another method is the measurement through a flexible wall permeameter (FWP). The hydraulic conductivity measured using the FWP is conducted in a confined cylinder in which water flow is forced into one direction. The main disadvantage of this type is being relatively more expensive and needs more time to perform the test compared to the RWP. This study is aimed at comparing three testing conditions to obtain an adjustment factor for the hydraulic conductivity test normally carried out in practice in order to cut down the time needed to perform the test as well as its cost. Different mixtures of sand and expansive clay addition were considered to examine the effect of expansive clay content on the values of the hydraulic conductivity. Tests results revealed that the clay content had a significant effect on the swelling potential, which was attributed to structural changes in the mixtures. The hydraulic conductivity of mixtures decreases with the increase in clay content. The hydraulic conductivity of mixtures tested using FWP was observed to be lower than that of mixtures tested using RWP at similar clay contents. The tests conducted enabled establishing a correction factor to adjust the hydraulic conductivity normally obtained in practice using rigid wall cells.

Effect of Desiccation on the Hydraulic Conductivity of Compacted Bentonite–Sand Blocks

This study investigated the impact of drying cracks on the hydraulic conductivity of compacted bentonite–sand blocks to support the construction of buffer barriers in an underground research laboratory for the disposal of China’s high–level radioactive waste. The hydraulic conductivity of an air-dried block (the worst storage case) was measured in a flexible–wall permeameter in the directions parallel and perpendicular to the direction of compaction according to ASTM D5084. The results were compared with the hydraulic conductivity of fresh blocks. Computerized tomography (CT) images were used to visualize the internal cracks of the blocks, and the swell index was measured to represent the blocks’ swelling properties. The test results revealed that compared with fresh blocks, the drying cracks increased the hydraulic conductivity of the blocks by less than fourfold. As demonstrated by the CT images, the drying cracks were healed after permeation with distilled water. The swell index of the block was unaffected by air drying, and the swelling of montmorillonite in bentonite contributed to the healing of the drying cracks.

Hydraulic conductivity of soil-bentonite backfill comprised of SHMP-amended Ca-bentonite to Cr(VI)-impacted groundwater

Hexavalent chromium (Cr(VI)) in groundwater impose serious health problems for human society. This study investigates the potential of using calcium (Ca) bentonite amended with sodium hexametaphosphate (SHMP) as a backfill constituent material in the soil-bentonite slurry trench wall to envelop the Cr(VI) impacted groundwater. The hydraulic conductivity (K) and consolidation of backfill comprising of 80 wt% sand and 20 wt% SHMP-amended Ca-bentonite were determined via flexible-wall permeameter tests and oedometer tests, respectively. Microstructure characterizations of the amended bentonites before and after contamination were also explored. The results indicated that when the permeated liquid changed from tap water to Cr(VI) solution, the tested specimens exhibited a 1.0 to 1.2-fold variation in short-term K, with all K values fall in range of 2.1 × 10−10 to 2.5 × 10−10 m/s. This mild variation may be attributed to terminate the tests without achieving chemical equilibrium. On the other hand, the Cr(VI) solution had insignificant effect on consolidation of the amended backfill, which is attributed to the dominated incompressible sand matrix skeleton in the backfill that withstood the consolidation pressure and shield the negative effects of the contaminated solution. The microstructure images revealed that the Cr(VI) resulted in relatively strong interlink between particles. Overall, the SHMP-amended bentonite is promising for enhancing Cr(VI) containment performance of the soil-bentonite slurry trench wall backfills.

Effect of Confining Conditions on the Hydraulic Conductivity Behavior of Fiber-Reinforced Lime Blended Semiarid Soil.

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (ksat) were determined. For FC fibers, an increase in fiber dosage caused ksat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, ksat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained.

Experimental Study for Assessing the Onset of Suffusion and Suffosion of Gap-Graded Soil

A modified triaxial shear test apparatus was used to investigate the factors influencing the onset of suffusion (migration of fine particles from soil without a change in volume) and suffosion (migration of fine particles from soil with a change in volume or a local collapse of the soil structure). A new criterion was developed to predict the seepageincited internal instability phenomena of suffusion or suffosion. A flexible wall permeameter, a seepage flow control system, and volume change measurement instrumentation were designed and manufactured for the study.

Experimental study on the permeability and self-healing capacity of geosynthetic clay liners in heavy metal solutions

Geosynthetic clay liners (GCLs), which have a very low permeability to water and a considerably high self-healing capacity, are widely used in liner systems of landfills. In this study, a series of experimental tests were carried out under complex conditions on typical commercial GCLs from China. In particular, the effects of pH values and lead ions (Pb2+) were tested in addition to other factors. The swelling properties of natural bentonite encapsulated between geotextile components in the GCLs were tested first. The swelling capacity was reduced rapidly at pH values < 3 and concentrations of Pb2+ >40 mM. Permeability tests on GCLs with different concentrations of lead ions were then performed by using the self-developed multi-link flexible wall permeameter, and data showed that increases in lead ion concentrations greatly improved the permeability. Finally, self-healing capacity tests were conducted on needle-punched GCLs under different levels of damage. Results showed that the GCLs have a good self-healing capacity with small diameter damage holes (2 mm, close to three times the original aperture), but with a damage aperture larger than 15% of the sample area, the self-healing capacity could not prevent leakage; hence, in certain situations it will be necessary to repair the damage to meet the anti-seepage requirement.

Effect of microstructure change on permeability of flax-fiber reinforced silty clay soaked with zinc-ion solution

With the application of fiber-reinforcement technology, the mechanical properties of silty clay are improved with fiber reinforcement. However, the variation of permeability coefficient and other parameters of flax-fiber reinforced silty clay have not been sufficiently studied. In this study, the permeability of flax-fiber reinforced silty clay soaked with zinc-contaminated solution under different osmotic pressure was tested by a flexible-wall permeameter, and the effects of zinc-ion concentration and confining pressure on the permeability of flax-fiber reinforced silty clay were studied. Genius XRF was employed to detect the types and quantity of metal elements in the specimens, thereafter, the reasons for the change of permeability were explained from chemical and microscopic perspective. The results showed that the permeability coefficient of flax-fiber reinforced silty clay decreased significantly with the increase of zinc-ion concentration in a low concentration (about 1–10 mg L−1). While in a high concentration (about 100 mg L−1), the permeability coefficient of flax-fiber reinforced silty clay changed little with the increase of zinc-ion concentration. While the flax-fiber reinforced silty clay was not soaked with zinc-ion solution, the permeability coefficient of the specimen increased with the increase of confining pressure. However, when the flax-fiber reinforced silty clay was soaked with zinc-contaminated solution, the permeability coefficient first decreased and then tended to be constant with the increase of confining pressure. With the increase of confining pressure, the porosity of flax-fiber reinforced silty clay decreased, and with the increase of zinc-ion concentration, the porosity of flax-fiber reinforced silty clay first increased and then decreased.