Falling-head Tests Research Articles

Improvement of field falling-head test and determination of hydraulic conductivity using Darcy’s equation

This study presents a novel permeameter design for field falling-head tests to determine vertical hydraulic conductivity (K) using Darcy's equation. The design features an open-ended standpipe with two ports for simultaneous measurement of hydraulic heads at both ends of the sediment column, enabling direct estimation of flow rate (q) and hydraulic gradient (i). Flow rate is calculated by differentiating the best-fit curve for water level change above the sediment, and the hydraulic gradient is derived from the head difference between the ports. Laboratory and field tests consistently demonstrated a strong linear relationship between q and i (R2 > 0.999), validating the applicability of Darcy's equation for this new permeameter design. The K values obtained using the proposed method matched those obtained using the Hvorslev equation method. Furthermore, the design allows for continuous measurement of heads after the falling-head permeameter test, facilitating the collection of time series data for the hydraulic gradient. When combined with a pre-determined K value, this enables calculation of time series for the seepage rate across the surface water/sediment interface. To demonstrate this capability, preliminary tests were conducted using commercially-available pressure transducers to monitor heads and obtain seepage time series. The results of these tests are also presented.

Is Biomethane Production from Common Reed Biomass Influenced by the Hydraulic Parameters of Treatment Wetlands?

Treatment wetlands (TWs) are Nature-Based Solutions which have been increasingly used worldwide for wastewater (WW) treatment as they are able to remove mineral and organic pollutants through both physical and biochemical processes. Besides the reusable effluent, the TWs produce, as their main output, plant biomass that needs to be harvested and disposed of at least once a year with significant management costs and causing the TW to be temporarily out of service. This study aims (i) to evaluate the potential of TWs’ biomass for local energy production and (ii) to understand the effects of TWs’ hydraulic conductivity (Ks) on the biomass biomethane yield. Specifically, this was addressed by determining the Biochemical Methane Potential of common reed (CR) (Phragmites australis) samples collected at three harvest times from the 10-year-old horizontal subsurface treatment wetland (HSTW) used as a secondary WW treatment system for the IKEA® store situated in Catania (Eastern Sicily, Italy). Furthermore, the falling-head test was conducted to assess the hydraulic conductivity (Ks) variation in the hydraulic conductivity (Ks) of the HSTW, in order to understand its influence on the CR biomethane production. The average methane content values were 130.57 Nm3CH4/tVS (±24.29), 212.70 Nm3CH4/tVS (±50.62) and 72.83 Nm3CH4/tVS (±23.19) in August, September, October 2022, respectively. Ks was correlated with both dry matter (R2 = 0.58) and fiber content (R2 = 0.74) and, consequently, affected the biomethane yield, which increased as the Ks increased (R2 = 0.30 in August; R2 = 0.57 in September). In the framework of a circular economy, the results showed the successful possibility of integrating bioenergy production into TWs. The research could contribute (i) to encouraging plant operators to reuse biomass from TWs for local energy production and (ii) to help plant operators to understand Ks effects on the biomass biomethane yield in order to increase the sustainability of the system and to reduce the maintenance costs.

Experimental Investigation of Red Soil Blended With Bentonite and Lime as a Landfill Liner

To control the migration of contaminants generated from the leachate, the liners are used in landfills. Compacted clay liners are widely used as liner materials due to the low value of hydraulic conductivity and large attenuation capacity. In the present work, an experimental study on red soil which is locally available is amended with bentonite use as a liner material for efficient leachate containment in landfills. The primary objective of this work is to determine the geotechnical properties of red soil blended with bentonite as a material for liners. The clay liners performance primarily depends on hydraulic conductivity. The hydraulic conductivity of the red soil is higher than the recommended limit (i.e.>10-7cm/s). Commercially available bentonite was blended with red soil to decrease the hydraulic conductivity. The permeability tests and falling head tests were conducted on 5%, 10%, 15%, and 20% bentonite by weight blended with red soil to evaluate hydraulic conductivity. From the experimental studies, it is clear that the red soil blended with 15% bentonite has a hydraulic conductivity value less than the requirements of landfill clay liner(i.e.<10-7cm/s). However, the Compressive Strength (CS) of blended red soil with 15% bentonite was less than 200 kPa, which is less than the minimum CS required for liner material. Lime was added to enhance the CS of the soil mixture and further studies were carried out. Swelling behavior is the major problem that is to be addressed during and after the construction of landfills. This study also presents the swelling behavior of red soil blended with bentonite and other additives.

Estimating the permeability of fractured rock masses for design of construction dewatering systems

A comprehensive data on dewatering and pumping-well systems installed in fractured rock is compiled and analyzed to estimate the permeability of fractured rock masses. The data covers construction activities of different nature and dewatering depths, and considered the richest of its kind. Due to the relatively small volume and the nature of rock masses involved in the analyzed systems, the effect of having predominant oriented fracture sets, and consequently different directional permeabilities (i.e., scale-dependent permeabilities) are minimal. As a result, the current study is a clear advancement on state-of-the art given that the vast majority of the related studies available in the literature are presented to estimate the directional permeability of rock masses. The analyses showed a significant discrepancy between the coefficients of permeability estimated from field packer and falling-head tests and those back-calculated from the actual discharge pumped out of rock masses using dewatering or pumping-well systems. Back-calculated permeabilities can be up to five orders of magnitude larger than the measured values. Such discrepancy increases with increasing permeability of rock mass. The sensitivity of the estimated permeability to the difference in rock formation, utilized fracturing index, test type, and depth of test is studied. A data-driven approach is used to develop a novel correlation between the measured and back-calculated coefficients of permeability. Accordingly, a procedure is proposed to estimate the permeability of fractured rock masses involved in construction dewatering as a function of the measured permeability and rock degree of fracturing.

Repeated falling-head method for in situ measurements of saturated hydraulic conductivity using a single cylinder

A simple, repeated falling-head (RFH) method, which uses an inexpensive portable cylinder to quickly determine field-saturated hydraulic conductivity (Kfs), is presented. A cylinder of radius r, inserted vertically from the soil surface to a depth d, is used as a water supply tank, through which water infiltrates into the soil. The falling-head test is repeated without allowing the cylinder to be drained entirely to eliminate the effects of the initial soil moisture conditions. Either change in the water level (H) in the water supply cylinder or strong linearity between the infiltration flux (qs) and H can be used to determine Kfs directly or by multiplying the slope with an empirical ring-installation scaling length, Lg; thus, no soil-dependent variable is necessary. To obtain the Lg value for various conditions, we carried out numerical experiments using HYDRUS (2D/3D) with a recently implemented reservoir boundary condition for six different soil textures, ranging from coarse soil (e.g., sand) to fine soil (e.g., silty clay loam), and two different ranges of water levels, 15 ≤ H ≤ 25 cm and 2 ≤ H ≤ 6 cm. Numerical results showed that the Lg has a strong linear dependence on d and r, where Lg increases as d and r increase. We propose a new linear model to determine Lg with optimized coefficients for each H range. Numerical results showed no significant differences in the estimated Kfs after the second repetition, confirming that repeating the falling head test twice is sufficient. The newly obtained Lg values were then applied to the experimental data obtained at multiple fields having different soil textures. The Kfs values determined using the RFH method agreed well with those measured using the field two-ponding depths steady-state method and/or the FH method in the lab. These results demonstrate the reliability of the proposed RFH method.

Hydraulic conductivity assessment of falling head percolation tests used for the design of on-site wastewater treatment systems

The suitability of a location for an on-site wastewater treatment process (for areas which lack access to centralised wastewater treatment systems) requires an assessment of the permeability of the soil into which the effluent will be discharged. In many jurisdictions this is determined using some type of in-situ percolation test. Falling head percolation tests, which give a value of percolation time (PT) that is empirically related to the notion of hydraulic conductivity, are widely used as they are relatively simple to carry out, but the test does not have a sound theoretical framework and test methods are not standardised internationally. In comparison, the saturated hydraulic conductivity of a soil obtained from a constant head well permeameter test is independent of test conditions, and so is a more suitable metric for design. A database of over 900 falling head tests carried out across a range of different subsoil types in Ireland has been collated, all with the inherent limitations of the existing regulative framework regarding the percolation test and soil texture assessment. These tests were then modelled using Hydrus 2-D numerical modelling simulations to determine equivalent field saturated hydraulic conductivity (Kfs) values and thereby provide a correlation with PT values across the range of subsoil conditions. In addition, falling head tests have been carried out in parallel to constant head permeameter tests in the field and compared against the relationship derived from the broad dataset of simulated results. This revealed an optimal solution by which to determine Kfs from the field permeameter test (using parameters recommended for most structured soils from clays to loams). The trendline based on Irish data was also compared against more generic formulations of the relationship between PT, and Kfs and shown to match closely, particularly the Reynolds (2016) ‘unified’ methodology. Finally, the Irish threshold PT limits for on-site wastewater treatment have been converted to Kfs values and compared against other international standards.

Impact of Sodium Carbonate on Seepage Reduction in Farm Irrigation Ponds

In this research, an economic layer using simple technology is evaluated to minimize seepage at the bottom of irrigation ponds. Since sodium carbonate diverges clay particles and decreases permeability by reducing porosity, it is recommended that sodium salts be used in mixed with soil at the bottom of irrigation ponds. The three types of soils were selected. First, the texture of the soils, second, chemical properties were determined for all three types of soils. Sodium carbonate were utilized in the percentages of 0, 2, 4, 6, 8, 10 and 12 by weight. Finally, the falling head test and the Scanning Electron Microscope (SEM) analysis were conducted. The results were illustrated as the tables and the graphs, and counter curves. The Results show that the soil 20% clay, the soil 15% clay and the soil 10% clay decrease seepage on average 42%, 64% and 71% respectively. The soil 10% clay has the greatest decrease of the three soil samples. Furthermore, in all three soil samples, the highest decrease in permeability was observed at 10% sodium carbonate. Overall, the results show that this pond sealer can be a suitable solution to reduce seepage in this type of pond.

Analysis of Soil Absorption Capacity of Rainwater in Biopori Infiltration Holes in Purwoyoso Village Semarang City

Drought and floods that hit Semarang City were caused by problems with water distribution and capacity. The ongoing conversion of land functions in the city of Semarang has resulted in reduced green open space and increased building density. This resulted in reduced infiltration of rainwater so that surface water runoff increased. Thus, causing a flood disaster that hit the city of Semarang in 2022, in which 7 out of 16 sub-districts were affected. This condition is exacerbated when rainfall is high and causes stagnant water because the existing drainage system is not optimal. The application of biopore infiltration holes in an effort to expand the rainwater infiltration area is a form of defense that can be carried out by the people of Semarang City in minimizing the occurrence of floods and groundwater crises. This study aims to analyze the absorption capacity of soil against rainwater in biopori infiltration holes in Purwoyoso Village. The method used is the Constant Head and Falling Head tests. The results of the groundwater absorption test showed that in sample B.1. and B.2. are 8.976.E-05 cm/sec and 9.488.E-05 cm/sec respectively. These results indicate that the absorption capacity of the soil in the biopori infiltration holes for rainwater is low or lacking.

Analytical study of falling-head test in confined aquifer with consideration of non-instantaneous injection

A falling-head test is a common method to estimate aquifer properties in which the water level in a well is increased suddenly, which is a key assumption for the data to be analyzed by traditional methods such as Cooper et al. and Hvorslev methods. However, there are situations where the water level increases in the well occurs for a relatively long period before it falls. In this case theoretically, there is no existing method to analyze the data. Hydrogeologists or geotechnical engineers still use the traditional methods to analyze the data even the water level increase is not instantaneous. This study derives a semi-analytical solution to describe water level change in this case. The mathematical model consists of the injection stage and water level fall stage. It is found that the water level mound induced by non-instantaneous injection leads to slower decrease of water level in the well comparing to the instantaneous injection. This study further analyses the errors of the estimated hydraulic properties if the data are analyzed by traditional methods. If calculated by Cooper et al. method, the storativity is underestimated but there is no impact on estimated hydraulic conductivity. The hydraulic conductivity calculated by Hvorslev method is underestimated and the error of underestimation increases with injection time and aquifer parameters. The actual hydraulic conductivity can be a few times of the estimated value for typical aquifer parameters in Hong Kong. Furthermore, a field experiment is conducted to compare the instantaneous method, non-instantaneous method and field data. The present solution fits the data well, and the errors of estimated parameters by instantaneous injection method are consistent with the conclusions in the error analysis.

Induced Bank Filtration: Hydraulic Testing of Pilot Filters

Hydraulic tests were performed on two pilot scale filters as part of a water treatment project in the village of Nersa, Karnataka, India. The filters use locally sourced alluvial material to filter E.coli contamination using natural processes that mimic those in Riverbank Filtration (RBF). Two pilot scale filters were tested, one containing locally sourced granular activated carbon (GAC) and one without. A falling head test and tracer test were preformed, and breakthrough curves were used to analyze the hydraulic performance. E.coli data were also collected, and percent removal was calculated to determine the effectiveness of the filters. Relative to the influent water, the E.coli removal percentage of Filter 1 (no GAC) was consistently high and ranged between 97.1% and 100% E.coli. The addition of GAC did not improve performance in this study. Overall, the effectiveness in bacteria removal observed in the non GAC filter warranted construction of a full-scale system.

Suitability of Engineering-Geological Environment on the Basis of Its Permeability Coefficient: Four Case Studies of Fine-Grained Soils.

The aim of the article is to compare two classifications systems of engineering-geological environment sustainability in terms of its permeability evaluated on the basis of permeability coefficient. The first evaluated classification assumes a permeable environment to be a positive characteristic in the engineering-geological assessment, while the other considers an impermeable environment as favourable. The four fine-grained soil materials were selected, as they had very similar, almost identical grains-size distribution, but different microstructure characterized by grains sphericity, angularity, and roughness. At the same time, the influence of changes in the density of soil materials (density index 10%, 30%, 60%, 90%) was analysed. Permeability coefficient was determined using six methods (empirical formulae, laboratory and microscopic analysis). The laboratory method falling head test (FHT) was taken as a reference test that reflected the actual water flow through the soil. It was found that with an increase in grain angularity and roughness (and a decrease in sphericity), the permeability coefficient was decreasing and this trend culminated along with gradual compaction. Moreover, the research shows that unsuitable methods may classify soil materials into wrong engineering-geological permeability classes, which may have negative consequences during engineering-geological or geotechnical assessment and cause subsequent problems in foundation engineering.

ASSESSMENT OF RESIDUAL SOIL PROPERTIES FOR SLOPE STABILITY ANALYSIS

Slope instability is a common natural geological hazard in tropical countries like Malaysia, with abundant residual soil and frequent rainfall. Over the years, these rainfalls have induced instabilities that lead to significant human and economic loss. To reduce the expected disastrous impacts due to rainfall-induced slope failure characterization of residual soil is necessary for evaluation of slope stability assessment. Therefore, this study aims to characterize the residual soil for numerical modelling of rainfall-induced slope failure and preliminary slope stability assessment so that future slope failure can be reduced. A series of experiments involving index properties tests and engineering properties tests were carried out on the residual soil samples collected from a slope located in UniversitiTeknologi Malaysia (UTM). Based on the particle size distribution and consistency the soil can be classified as high plasticity silt (MH). The maximum dry unit weight and optimum moisture content are 13.17kN/m3 and 30 %, respectively. Saturated hydraulic conductivity from the falling head test is 2.32055E-07 m/s, while the saturated gravimetric water content was 54%. The effective cohesion and angle of the internal fraction were 8 kPa and 32°, respectively. The average undrained shear strength and unconfined compressive strength were 105 kPa and 43 kPa, respectively. The result obtained in this study was utilized for the preliminary rainfall slope stability assessment in tropical residual soils by simulating rainfall of different intensities and duration on a typical slope profile using PLAXIS 2d. The results show that due to the low hydraulic conductivity and fine-grained nature of the soil, the slopes in the study area are more critical to the low intensity and long duration rainfall events (I≤4Ks). The highly intense and short-duration rainfall (I≥8Ks) has no significant effect on the safety of the soil, as most of the precipitation will contribute to runoff, and only a minor amount of water will infiltrate into the slope.

THE PROPOSED GEOBEADS ADDITION AS LIGHTWEIGHT FILL MATERIAL

The study aimed to develop an alternative material for dam and road embankments, especially in the area with soft soil, using Geobeads. There are many problems constructing embankments on soft soil, such as low bearing capacity, excessive and differential settlement, and slope stability. The subgrade must be stable to resist the weight of the fill construction and upper structure. The lightweight fill material is commonly used as an alternative to reduce the excessive and differential settlements by reducing the weight of landfills on the soft soil subgrade. In this study, the laboratory test was conducted to investigate the influence of Geobeads (GB) additions as lightweight fill material both as the dam embankment and the road embankment. This study aims to find a combination of GB, sand, and cement to fulfill the standard as an embankment material. Investigation of physical and mechanical properties represented that light embankment can be an alternative on soft soil. The Indonesia National Standard, 8062:2015, and the General Specifications for Road and Bridge Construction Work were guidelines for embankment cases. The falling head test executes the permeability coefficient. The CBR test was conducted based on ASTM D1883. The specimen has varied the percentage of EPS addition (20%, 30%, 40%) with 14 days of curing time. Based on the test results, both the permeability coefficient value and the CBR value decreased along with the increase in the percentage of EPS, where the coefficient of permeability (k) of the specimens around 10-5 cm/s and the lowest CBR at 40% GB was 30.02% which is the range still used as embankment material.

Hydraulic properties of unsaturated calcarenites by means of a new integrated approach

Most infiltration and water retention models for unsaturated porous media proposed in the literature often are based on simplified representations of the pore system and use the matric head as the main state variable.An integrated study on the hydraulic properties of homogeneous calcarenites with a complex pore network is presented, aimed at assessing water infiltration and retention mechanisms, starting from dry to wet conditions under high water inflow.Medium-grained grainstones and fine-grained packstones were used as material for laboratory testing and model set up. Petrophysical characterization and bimodal distribution of pore volume was obtained by standard and unconventional procedures. Permeability test under saturated conditions was performed with constant and falling head tests. Falling head infiltration tests at bench scale were carried out to estimate the hydraulic properties of the materials under unsaturated conditions.Unsaturated hydraulic relationships such as the soil water retention curve (SWRC) and hydraulic conductivity function were examined. The advection–diffusion form of Richard’s equation, together with the pore bundle model and dual porosity concept under equilibrium conditions represent the theoretical framework used to investigate the unsaturated hydraulic behavior of the calcarenites in the falling head infiltration test. The SWRC, relative hydraulic conductivity and celerity were determined through the capillary theory and pore bundle concept considering the bi-modal nature of the pore-size distribution. Theoretical solutions and model predictions were compared with experimental data, which demonstrated the dominant control of macro-porosity on water flow and infiltration rate. In particular, our experimental results indicate that the wetting front propagates mainly through the macropores with a gravity driven flow velocity higher than the diffusive flow through the micropores. The effect of texture, degree of saturation and boundary conditions on infiltration dynamics is discussed.

Pore water pressures and hydraulic conductivity in the slip zone of a clayey earthflow: Experimentation and modelling

Rainfall is among the most relevant triggering factors of landslides. With the aim of defining a model of the influence of rainfall on deep landslides, this paper presents data of a long-term monitoring of pore water pressures in a clayey earthflow, and the results of many field permeability tests carried out with several procedures. Pore water pressures are being monitored in the Costa della Gaveta slope since 2005. In the last years, new instruments have been installed and permeability tests have been carried out in the stable formation, in the landslide body and in the slip zone. The hydraulic conductivities of the three different zones of the subsoil have been evaluated by two types of field tests: falling head tests (by Casagrande piezometers and test wells), and localized constant head tests (by a permeameter ad hoc designed). The experimental data show that: a) pore water pressures along the slip zone respond to rain more than in the landslide body and in the stable formation, even at about 25 m depth; b) the hydraulic conductivity ksz of the slip zone is much higher than that of the landslide body, kl, in turn higher than the hydraulic conductivity of the stable formation, kf. The numerical 3D modelling of steady-state reference conditions and of transient processes caused by the historical rainfall series shows that the occurrence of ksz higher than kl and kf determines an overall drainage effect which makes the global limit equilibrium safety factor SF greater than that evaluable for other possible conditions. On the other side, even the lowest measured hydraulic conductivity ksz provides seasonal rain effects on water pressures along the slip surface such to determine significant SF variations in phase with the observed seasonal displacement rates.

Evaluation of the hydraulic conductivity for MSW using pilot plant test- A case study of Baghdad city/Iraq

The hydraulic properties of municipal solid waste (MSW) have been regarded as core factors affecting landfills’ flows. To successfully design and applied, information on the conductivity of MSW is required. A laboratory examination of MSW’s hydraulic conductivity in Baghdad City is presented in this study and assesses the influence of waste compaction on hydraulic conductivity parameter. A hydraulic conductivity test was carried out in a laboratory-scale cell using three mixtures of fresh shredded MSW samples ‘SAM1’, ‘SAM2’ and ‘SAM3’ collected from the households Baghdad City. The saturated vertical hydraulic conductivity was quantified according to different types of compactions using a falling head test. A clear trend of decreasing hydraulic conductivity with increasing compaction degree was highlighted after the monitoring process, reflecting the impact of varying waste densities and fine particles’ movement in the column. This experiment shows that the average hydraulic conductivity values at 50, 70, and 90 degrees of compaction were 1.23×10-4 m/s, 0.96×10-4 m/s, and 2.55×10-5 m/s, respectively. The results distinctly showed that the MSW’s hydraulic conductivity could be significantly affected by vertical compaction that is fundamentally attributed to accretion in density resulting in the low void ratio.

Сравнительное исследование проницаемости грунтовых прослоек из смеси глины и материала термитников Macrotermes gilvus Hagen и бентонита

The liner has a role as a sealing or waterproof layer that was made to prevent water to be absorbed by the soil. A good liner is made within the minimum hydraulic conductivity (k) within the requirements of 1.0E-07 cm/s. This study was conducted to determine the extent of the difference between hydraulic conductivity (k) bentonite and termite nest (Macrotermes gilvus Hagen) as one of the materials that have the potential to obtain the small value of hydraulic conductivity (k). This research was conducted by examining the effect of hydraulic conductivity (k) value on the percentage of additives, such as bentonite and termite nest material (M. gilvus Hagen), and then compared the hydraulic conductivity (k) values of those two materials. The variations in the additive content percentage are 5%, 15%, and 30% with laterite as a base material. Based on the results of the falling head test at a minimum density of 95% γdmax, the smallest hydraulic conductivity (k) value was obtained by bentonite with 30% mixed percentage level of 6.9390E-08 cm/s and the smallest hydraulic conductivity (k) value of termite nests was 1.2646E-07 cm/s with the content percentage of 5% mixture.

Assessing Gas Leakage Potential into Coal Mines from Shale Gas Well Failures: Inference from Field Determination of Strata Permeability Responses to Longwall-Induced Deformations

This paper summarizes the changes in permeability at three boreholes located above an abutment pillar at a longwall coal mine in southwestern Pennsylvania. The motivation of this study was to better characterize the potential interaction between shale gas wells and the mine environment, through measurement of permeability changes in the coal mine overburden caused by mining-induced deformations. Measuring permeability changes around boreholes affected by longwall mining is an effective method to indicate changes in the fracture network above longwall abutment pillars and estimate the capacity for gas flow from shale gas wells to the mine environment. This study measured permeability through falling-head slug tests at different longwall face positions during the mining of two longwall panels on either side of the test abutment pillar where the test boreholes were located. Three test boreholes were drilled to different depths above the active mining level, and they had screened intervals to evaluate the response of different stratigraphic zones to mining-induced stresses. The results showed that the permeability around the slotted intervals of each borehole increased pre-mining to post-mining, and the permeability increased from mining of the first longwall panel to mining of the second one, adjacent to the pillar.

Impact of Sedimentation on Water Seepage Capacity in Lake Nakuru, Kenya

Accumulation and deposition of sediments in waterbody affect the seepage capacity that could lead to improper water balance and results in the water level rise. This study analysed the influence of sedimentation on seepage capacity in Lake Nakuru and the impact of sediment characteristics to the water seepage and the flow rate formation at the lake bed level. The study was performed by sampling and analysing the sediment cores from two locations in the lake. The sediment hydraulic properties, i.e., moisture and porosity, particle sizes, and hydraulic conductivity, were determined using the oven-drying method, sieve analysis, hydrometer analysis, and falling head tests, respectively. The results showed that the lake sediment sample from location P1 had an average ratio of 39.38% for silty soil, 34.00% for clayey sediment, and 26.63% for fine-sand sediment particles with the maximum permeability coefficient of 3.37 ∗ 10 − 5 cm/s, while the one from location P2 had an average ratio of 63.17% for sand, 20.17% for fine particles, and 16.67% for gravels with the maximum permeability coefficient of 0.010793 cm/s. The hydraulic conductivity of sediment sample from location P1 and P2 increased along the core depth. This could lead to the rise of water level due to the decreases of water movement induced from the sediment cementation in the top layers under the waterbody. Sedimentation affects Lake Nakuru water volume and water balance; hence, there is a need to control the inflow of sediment resulting from anthropogenic activities in the watershed.

Characterization of Air Void in Porous Asphalt Mixture Using Image Techniques and Permeability Test

In this study, air void contents and distributions of porous asphalt mixtures along the vertical and horizontal directions were quantitatively measured on planar images. Air void contents were determined using some image techniques; while the permeability was measured by the falling head test. Two aggregate gradations (G1 and G2) and three blow numbers (30, 40, and 50) were chosen to explore the effects of gradation and compaction effort on the porosity and permeability. Results showed that porosities and permeabilities are symmetrically distributed along the middle of the specimens; the porosities and permeabilities got the minimum values around the middle zone. A finer gradation or a significant compaction effort generally led to a lower porosity and permeability coefficient. In the horizontal direction, the air void content showed an increasing trend from the outside layer to the inner layer, indicating the nonuniformity of porosity distribution.