Laboratory Permeability Tests Research Articles

Effect of water pressure on permeability of foam-conditioned sands for EPB shield tunneling

Foam conditioning is a widely adopted technique in earth pressure balance (EPB) shield tunneling for the purpose of reducing sand permeability and preventing water spewing. The permeability of foam-conditioned sands differs from that of natural sands due to the presence of foam bubbles. This study investigated the effect of water pressure on the permeability of foam-conditioned sands using novel laboratory permeability tests. The water pressure, for the first time, is decoupled with the hydraulic gradient, owing to a newly developed permeameter with the controllable downstream hydraulic pressure in the laboratory. The results show that the permeability is significantly affected by the water pressure, and the effect is also predominantly dependent upon the foam injection ratio. The initial hydraulic conductivity increases with the increasing water pressure, while the initial stable period duration decreases. The water-plugging structure formed by foam bubbles and sand particles is prone to be damaged under high water pressure due to the shrinkage of foam bubbles. This means that the existing permeability tests with low water pressure underestimate the permeability of foam-conditioned sands. The underlying mechanism of water pressure in modifying the permeability of foam-conditioned sands is also examined from a particle-scale perspective.

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.

Effect of Various Aspects of Joints on Permeability of Jointed Glacial Till, Northeastern Ohio

ABSTRACT Glacial till bluffs along Lake Erie's shoreline, northeastern Ohio, contain three sets of joints that influence the hydraulic behavior of till mass like joints in rock influence the hydraulic behavior of rock mass. According to the Unified Soil Classification System, the till classifies as low plasticity silt to low plasticity clay, with a clay content of 36–41 percent. Mineralogically, it consists of quartz, illite, and kaolinite. The joints in till are either open or filled with sand, silt, or both from the overlying lacustrine material or with disintegrated till from the joint walls. We used double-ring infiltration and dye tests to estimate field permeability. Laboratory permeability tests were performed on dry and saturated samples of till material, with manually created joints that were either kept open or filled with sand or disintegrated till material to simulate field conditions. Field and laboratory test results showed that permeability of jointed till depended upon whether the joints were open or filled, the nature of the joint-filling material, and the water content of the till (dry versus saturated) and that permeability generally decreased with increasing test time. Dry samples exhibited a substantially larger decrease in permeability than saturated samples, with the largest decrease occurring during the first 24 hours. Open joints in dry samples collapsed during the test procedure, and the permeability of these samples was generally similar to the permeability of the collapsed till material. Permeability tests on saturated samples with open joints were inconclusive. We present a comparison of field and laboratory test results.

Numerical Research on Migration Law of Typical Chlorinated Organic Matter in Shallow Groundwater of Yangtze Delta Region

With the reform of China’s urbanization increasing in popularity, the security issues posed by urban groundwater, especially groundwater in industrial areas, have attracted scholars’ attention. This research aimed to predict and quantify the migration process of contaminants in a microconfined aquifer by conducting a groundwater contamination investigation in an abandoned chemical plant in the Jiangsu Province of China. First, data such as regional hydrogeological parameters and types of contaminants were obtained via hydrogeological drilling, groundwater well monitoring, pumping tests, and laboratory permeability tests, which helped identify the most serious pollution factor: chloroform. Then, a groundwater flow model was built using the Groundwater Modeling System (GMS) and verified using the general-purpose parameter estimation (PEST) package. In addition, based on the three-dimensional multi-species model for transport (MT3DMS) in GMS, a transport model was established. The results illustrate that the plume range of chloroform diffuses with water flow, but, because of its slow diffusion rate and inability to degrade naturally, the concentration of the contaminant has remained several times higher than the safety standard for a long time. The contaminant spread vertically to the soil layer above the microconfined aquifer under pressure, resulting in direct pollution. In addition, the contaminant in the microconfined aquifer is anticipated to migrate down to the clay layer and become enriched. However, the first confined aquifer has not been seriously polluted in the past 20 years. Finally, a sensitivity analysis of the parameters shows that groundwater contamination in the Yangtze delta region is greatly affected by precipitation recharge and hydraulic conductivity.

Moisture Movement Analyses for Coal Stockpiles

Flowslides and stability issues have occurred periodically within stockpiles of coking (metallurgical) coal at coal processing plants and export terminals in Queensland’s Bowen Basin, and to a lesser degree in New South Wales, since the early 1970s. A description of the issue and summary of research at James Cook University from 1973 to 2000 was published in ACARP Report C4057. Despite this work, coal stockpile flowslides remain a significant risk at mine and port stockpiles due to their initiation without warning and dramatic consequences. To be able to adequately model the redistribution of moisture that leads to collapse of a stockpile and then conduct realistic stability analyses for design of preventative measures remains an elusive prospect. This paper therefore updates the previous work with results from SEEP/W transient seepage modelling within a 12m high 14,700 tonne coal stockpile constructed at Hay Point in late 1991 for which initial moisture content, pore pressures at the stockpile base, outflows from subsoil drains and final density and moisture profiles were measured. The model was based on results of laboratory permeability and column drainage tests on specimens taken from a composite bulk sample obtained at the time of stockpile construction. The coking coal product was from an operation with a known history of stockpile instability. Results were found to correspond well with pore pressures measured at the stockpile base and the stockpile’s final moisture profile provided account was taken of a thin higher permeability zone just above the subgrade. The approach adopted and parameters developed provide a significant advance in modelling of moisture movements within production coal stockpiles, with a view to subsequent slope stability analyses.

An anisotropic pore-network model to estimate the shale gas permeability

The permeability of shale is a significant and important design parameter for shale gas extraction. The shale gas permeability is usually obtained based on Darcy flow using standard laboratory permeability tests done on core samples, that do not account for different transport mechanisms at high pressures and anisotropic effects in shales due to nano-scale pore structure. In this study, the permeability of shale is predicted using a pore network model. The characteristics of pore structure can be described by specific parameters, including porosity, pore body and pore throat sizes and distributions and coordination numbers. The anisotropy was incorporated into the model using a coordination number ratio, and an algorithm that was developed for connections of pores in the shale formation. By predicting hydraulic connectivity and comparing it with several high-pressure permeability tests, the proposed three-dimensional pore network model was verified. Results show that the prediction from the anisotropic pore network model is closer to the test results than that based on the isotropic pore network model. The predicted permeability values from numerical simulation using anisotropic pore network model for four shales from Qaidam Basin, China are quite similar to those measured from laboratory tests. This study confirmed that the developed anisotropic three-dimensional pore network model could reasonably represent the natural gas flow in the actual shale formation so that it can be used as a prediction tool.

Lessons from the Case History of a Massive Landslide Dam

A massive landslide created a natural dam on two tributaries of Jhelum River near the town of Hattian Bala in Kashmir in October 2005. The landslide was triggered by a 7.6 Mw earthquake. The resulting unconsolidated dam and water impoundment upstream carried hazard potential of downstream damage to both infrastructure and population due to potential flooding caused by its breach. Comprehensive investigations and monitoring were implemented to analyse dam stability. Fresh topographic profiles were generated. Samples of the matrix materials were utilized in the laboratory investigations including grain-size analysis, laboratory electrical resistivity and permeability tests at varying densities and degrees of saturation, and sediment concentration assessment in the seepage discharge. A noninvasive geophysical method was employed together with new topographic information to develop transient subsurface pictures and to assess the advancement of seepage fronts within the dam body. Internal erosion/filtering potential of the matrix material was assessed by comparing grain size distributions with those of the earlier failed dams. Upstream inflows, downstream discharges, daily precipitation, and lake levels monitored during the study period were utilized in hydrological data analysis in an attempt to assess the potential seepage volume. A combination of empirical, analytical, and numerical methods and simulations, together with laboratory and field investigations, led to the interpretations regarding short- and long-term stability of the dam. This paper highlights alternative methods of investigation employed differently from those used by other national and international agencies in analysing the failure potential of this natural dam. It offers lessons learned from a case history that can be beneficial in future evaluation of seepage-induced failure of similar natural features.

COAL PERMEABILITY ANISOTRTOPY ESTIMATION BY FILTRATION EXPERIMENTS AND FRACTURE ANALYSIS RESULTS

Experimental studies of the structure of medium-volatile bituminous coal taken from the Leninsk region of Kuzbass are performed. The main properties of endogenous cleavage fractures are determined. The dependence of coal absolute permeability on uniform compression of samples is experimentally explored. Laboratory permeability tests were conducted in the direction parallel to master cleavage fractures and bedding planes. The obtained values are typical for intensely fractured coals. Using the known models, the dependence of coal permeability on stress conditions is obtained for the directions parallel to master and side cleavage. The anisotropy of coal horizontal permeability is determined taking into account the properties of endogenous cleavage fractures. Change in coal permeability with seam depth is estimated in conditions of the Leninsk region of Kuzbass. The permeability-depth data were obtained for the conditions of uniaxial strain perpendicular to layered structure and endogenous cleavage planes.

Analysis of rainfall-triggered landslide in Baleagung Village, Magelang Regency, Central Java

The majority of Magelang Regency is considered as intermediate and high susceptible areas against landslide. As happened in Baleagung Village in January 2018, a landslide has damaged local residency buildings. The landslide occurred because of high-intensity rainfall on the day before. Meanwhile, cracks formed in several areas that were indicated by the slope around the village were still actively moving. Therefore, mitigation is urgently needed to minimize the risk of further landslide movement. This study aimed to analyze the mechanism of ground movement at Baleagung Village which was affected by rainfall. This research was conducted by using back-analysis method to determine the initial groundwater level conditions and its effect on the slope stability. Soil parameters were obtained by laboratory testing and permeability tests in the field. Subsequently, rainfall data was collected from Himawari-8 satellite and used as the data input parameter for numerical analysis using SEEP/W and SLOPE/W. The results obtained from back-analysis showed that rainfall infiltration into the soil affected the degradation of safety factor value that was caused by the increase of pore-water pressure and the decrease of effective stress in a certain period. The degradation of safety factor was caused by the increasing of soil saturation degree when water infiltrated into the ground.

Experimental study of the intrinsic permeability of municipal solid waste

Changing patterns of municipal solid waste (MSW) management, for example sorting for recycling and mechanical–biological treatment (MBT), will change the nature of the residual material going to landfill and in particular its intrinsic permeability. This is an important parameter, not least because of its influence on gas and leachate flows and the ramifications for gas and leachate management. This paper reports the results of laboratory permeability tests on specimens of MSW recovered from boreholes drilled in a Chinese landfill, under both liquid and gas flow. The test results are used to assess the intrinsic permeability of the waste, and are compared with corresponding data from raw and MBT municipal solid wastes from developed countries in the context of differences in waste composition, porosity and particle size. For the Chinese waste, the intrinsic permeability decreased with depth, while at a given depth the permeability determined with gas flow was consistently larger than that determined with liquid flow. Intrinsic permeabilities determined in liquid flow showed no clear trend of variation with effective particle diameter d10, but reduced with drainable porosity (the drainable porosity, ne, being a more appropriate and useful measure than the total porosity, n). Conversely, intrinsic permeabilities determined in gas flow showed a clear decrease with decreasing d10, but no consistent variation with porosity. These differences are potentially significant in assessing the impacts and interactions between gas and liquid flows; some reasons for them are suggested.

How to Improve the Quality of Laboratory Permeability Tests in Rigid-Wall Permeameters: A Review

ASTM D2434, Standard Test Method for Permeability of Granular Soils (Constant Head) (Withdrawn 2015), and ASTM D5856, Standard Test Method for Measurement of Hydraulic Conductivity of Porous Material Using a Rigid-Wall, Compaction-Mold Permeameter, are used to measure the saturated hydraulic conductivity, Ksat, of soil specimens in rigid-wall permeameters (RWPs). Several laboratory conditions and settings explain why the tests do not give Ksat values but unsaturated hydraulic conductivity, K(Sr), values for a degree of saturation, Sr, that is often in the 80–85 % range. It is suggested to improve ASTM D2434 and ASTM D5856 by adding two requirements: (1) use a watertight-and-airtight RWP (a control method is provided), and (2) use a mass-and-volume method to obtain the true Sr value of the tested specimen. To illustrate potential detrimental impacts of current standards, the article describes a case where sand was planned to be used as a filter layer for a solid waste project. Large quantities of sand had been delivered at the construction site. The Ksat value of the sand, as compacted, had to exceed 10−4 m/s to satisfy a bylaw. To prove this, two laboratories followed ASTM D2434 for their tests but found K values of 5−8 × 10−5 m/s. The project engineers asked the authors to make verifications. The prior tests were redone and yielded similar K values. However, it was found that the real Sr value was close to 80 % instead of being assumed to be 100 %. Other tests were performed after using vacuum and deaired water in a watertight-and-airtight permeameter: the specimens reached Sr = 100 % and gave Ksat values of about 2 × 10−4 m/s, 3–4 times higher than initial tests. As a result, the already delivered sand satisfied the bylaw condition and there was no need to return large quantities of sand already delivered, to purchase a new type of sand after having done laboratory tests, and to have a time delay in construction, all these items having a high economic impact.

Optimal ranges of soil index properties for diesel containment using compacted barriers

Results of laboratory and field permeability tests performed in order to specify optimal ranges of soil index properties for the containment of organic liquids are presented. Liners for waste containment are often constructed with the use of fine-grained, high-plasticity natural soils, which normally present low hydraulic conductivity and are capable of attenuating inorganic soluble chemical species. However, because of the low polarity of most non-aqueous phase fluids (NAPLs), the effectiveness of fine-gained soils for NAPL containment is controversial. Several permeability tests were performed using soils with different characteristics and compaction energies. As expected, tests performed using diesel (low dielectric constant) presented higher permeability coefficients (k) than water in fine-grained soils. Concerning the diesel tests, soils compacted in the normal Proctor energy were unable to achieve values of k ≤ 1 × 10–8 m/s recommended for petroleum derivative storage areas. Soils compacted in the modified Proctor energy within specific ranges of index properties were able to fulfil regulatory requirements. Index ranges were defined towards long-term liner performance and were used to construct experimental landfills. Field and laboratory permeability tests were performed in the landfills, validating the applicability of the proposed ranges, although some adjustments are applied for better field performance.

Potential heavy metal pollution of soils from artisanal automobile workshops: the case of Suame Magazine, Ghana

This study has investigated the levels of heavy metal pollution in the soil at a typical automobile hub where a lot of oil waste, generated through vehicular maintenance and servicing, is spilled indiscriminately into the environment. Twenty-nine (29) soil samples were taken from eight (8) locations up to a depth of 2 m (i.e., the depth to water table) in the area and analysed for the presence of Pb, Cd, Cu, Zn, Cr, Fe, Mn, and Ni. In addition, laboratory permeability and grading tests were conducted on the samples to ascertain their influence on the mobility of the heavy metals. The study results indicated that the soil in the area is well graded with coefficient of permeability in the order of 10− 3 mm/h and mostly composed of silt, sand, and gravel with little amount of clay and less than 10% organic matter content as well as a pH range of 4.04–7.74. The levels of heavy metal contamination in the soil were in the order Pb > Cd > Zn > Mn > Cu > Fe > Cr > Ni. The soil quality up to a depth of 0.6 m was found to be highly polluted with the heavy metals based on pollution load index and degree of contamination assessments. In addition, a combination of Pearson’s correlation and cluster analyses of the heavy metal associations revealed the pollution source to be anthropogenic and must, therefore, be checked due to its potential to contaminate the shallow groundwater in the area and associated health implications.

Change of hydraulic conductivity of cohesive soils due to consolidation treatments with expanding resins

Settlements of ground subjected to foundation load are often due to both natural and/or anthropogenic causes, such as differential consolidation, seepage, periods of drought alternating with heavy rainfalls, growth of tree roots, sewer leaks, vibrations induced by vehicle traffic, excavations, or construction defects. Techniques of soil consolidation and stabilization by means of injection of polyurethane expanding resins have been efficiently used to mitigate or even solve this issue. The efficiency of the resin injection treatment has been well documented also thanks to the develop of a procedure of planning and monitoring which combines traditional geotechnical tests with the application of electrical resistivity tomography, which is strongly sensitive to the presence of water or voids. The combination of these survey methodologies allows to recognize the effect of injection in terms of soil compaction and water migration, a key factor for understanding the phenomenon and planning of resolutive interventions. The present study follows a previous work aimed at evaluating the increase in the geotechnical performance of cohesive soils treated by injection of expanding resins (same soil, resin, at the same site) and integrates it by focusing on the quantification of the effects of consolidation treatments, by means of expanding resins injection, on hydrologic properties of cohesive soils, focusing on saturated hydraulic conductivity measurements. Laboratory permeability test, performed in triaxial cell at different stress conditions and hydraulic gradients, were performed on undisturbed samples collected on “natural (non-treated)” and “treated soils”, before and after the injection of resin (MAXIMA ® by GEOSEC ® ) in a full-scale test site characterized by the presence of continuous and homogeneous cohesive soils, (clay and silts). The investigated soil is classified as CH or CL soil, very firm and apparently overconsolidated. The study shows how the treatment is able to modify the characteristics of hydraulic conductivity of the soil. The injected resins partly follow pre-existing weaknesses and partly impregnate homogeneous and continuous masses of soil in a capillary way, giving it, in addition to the already documented greater mechanical strength, a lower hydraulic conductivity. The electrical resistivity investigations allow to appreciate the volumes affected by the treatment to which the variations of the measured properties can be attributed.

Characterization of macropore structure of Malan loess in NW China based on 3D pipe models constructed by using computed tomography technology

Malan loess is a grayish yellow or brownish yellow, clastic, highly porous and brittle late Quaternary sediment formed by the accumulation of windblown dust. The present-day pore structure of Malan loess is crucial for understanding the loessification process in history, loess strengths and mechanical behavior. This study employed a modern computed tomography (CT) device to scan Malan loess samples, which were obtained from the east part of the Loess Plateau of China. A sophisticated and efficient workflow for processing the CT images and constructing 3D pore models was established by selecting and programming relevant mathematical algorithms in MATLAB, such as the maximum entropy method, medial axis method, and node recognition algorithm. Individual pipes within the Malan loess were identified and constructed by partitioning and recombining links in the 3D pore model. The macropore structure of Malan loess was then depicted using quantitative parameters. The parameters derived from 2D images of CT scanning included equivalent radius, length and aspect ratio of pores, porosity, and pore distribution entropy, whereas those derived from the constructed 3D structure models included porosity, coordination number, node density, pipe radius, length, length density, dip angle, and dip direction. The analysis of these parameters revealed that Malan loess is a strongly anisotropic geomaterial with a dense and complex network of pores and pipes. The pores discovered on horizontal images, perpendicular to the vertical direction, were round and relatively uniform in shape and size and evenly distributed, whereas the pores discovered on vertical images varied in shape and size and were distributed in clusters. The pores showed good connectivity in vertical direction and formed vertically aligned pipes but displayed weak connectivity in horizontal directions. The pipes in vertical direction were thick, long, and straight compared with those in horizontal directions. These results were in good agreement with both numerical simulation and laboratory permeability tests, which indicate that Malan loess is more permeable in the vertical direction than in the horizontal directions.

An optimized transient technique and flow modeling for laboratory permeability measurements of unconventional gas reservoirs with tight structure

Considering the significance of pressure-dependent-permeability in characterizing fluid flow and production from gas reservoirs and the inaccuracy of the conventional transient technique in laboratory permeability measurements of core samples from unconventional reservoirs with tight structure and strong sorption potential, the conventional transient technique is optimized by using two equal-sized gas reservoirs mounted in the up and downstream sides of the experimental setup and creating same magnitude of pressure pulses in each reservoir concurrently. Applicability of the optimized transient technique is examined through both numerical simulation and laboratory tests. A mathematical model is firstly developed to numerically investigate fluid flow behavior in time and space domain. The results from numerical simulation showed that the optimized technique can greatly improve the efficiency and accuracy of the measurement, because a steady flow state as a function of time can be achieved much faster in comparison with the conventional transient technique when the same magnitude of initial pressure difference is established between the two ends of the sample. Given the difference in experimental design and procedures between the conventional and the optimized technique, it is questionable whether currently used analytical solutions developed for the conventional technique for permeability calculation can be applied for the optimized technique. Therefore, an analytical solution, corresponding to the optimized transient technique, has been then theoretically derived. It is finally experimentally verified that accurate permeability results can be obtained based on late-time pressure responses by the derived analytical solution. The optimized experimental method is capable of extending the application of the transient technique into permeability measurements of rocks with tight structure and strong gas sorption potential, providing a more reliable approach for laboratory permeability tests.

The Characteristics of Hydrogeological Parameters of Unconsolidated Sediments in the Nakdong River Delta of Busan City, Korea

This study dealt with the characteristics and the interrelations of hydrogeological parameters such as hydraulic conductivity, dispersivity and effective porosity of unconsolidated sediments for providing the basic data necessary for the planning of the management and preservation of groundwater quality in the Nakdong River Delta of Busan City, Korea. Groundwater quality in this area has been deteriorated due to seawater intrusion, agricultural fertilizer and pesticide, industrial wastewater, and contaminated river water. The physical properties (grain size distribution, sediment type, sorting) and aquifer parameters (hydraulic conductivity, effective porosity, longitudinal dispersivity) were determined from grain size analysis, laboratory permeability test and column tracer test. Among 36 samples, there were 18 Sand (S), 7 Gravelly Sand (gS), 5 Silty Sand (zS), 5 Muddy Sand (mS), and 1 Sandy Silt (sZ). Hydraulic conductivity was determined through a falling head test, and ranged from <TEX>$9.2{\times}10^{-5}$</TEX> to <TEX>$2.9{\times}10^{-2}cm/sec$</TEX> (0.08 to 25.6 m/day). From breakthrough curves, dispersivity was calculated to be 0.35~3.92 cm. Also, effective porosity and average linear velocity were obtained through the column tracer test, and their values were 0.04~0.46 and 1.06E-04~6.49E-02 cm/sec, respectively. Statistical methods were used to understand the interrelations among aquifer parameters of hydraulic conductivity, effective porosity and dispersivity. The relation between dispersivity and hydraulic conductivity or effective porosity considered the sample length, because dispersivity was affected by experimental scale. The relations between dispersivity and hydraulic conductivity or effective porosity were all in inverse proportion for all long and short samples. The reason was because dispersivity was in inverse proportion to the groundwater velocity in case of steady hydrodynamic dispersion coefficient, and groundwater velocity was in proportion to the hydraulic conductivity or effective porosity. This study also elucidated that longitudinal dispersivity was dependent on the scale of column tracer test, and all hydrogeological parameters were low to high values due to the sand quantity of sediments. It is expected that the hydrogeological parameter data of sediments will be very useful for the planning of groundwater management and preservation in the Nakdong River Delta of Busan City, Korea.

The study of the effect of internal structure on permeability of porous asphalt

X-ray computed tomography (CT) and laboratory permeability techniques were applied to study the internal properties of porous asphalt mixture. Specimens containing aggregate of different gradations and of different mineral compositions were prepared in the laboratory. The air voids of all the specimens were determined in the laboratory and the specimens were then scanned in X-ray CT. The same samples were then tested for laboratory permeability. The active air voids and contact points of aggregate with nearby aggregate particles were determined from X-ray CT images. The laboratory permeability test results were found in comparison with X-ray CT values of voids’ internal connectivity. A comparatively high permeability value was observed for porous asphalt with maximum aggregate size irrespective of its mineral composition. The size of air voids and volume of active (connected) air voids were also found high for mixtures made up of large aggregate size. The difference in mineral composition of aggregate was found to have considerably less effect on permeability of porous asphalt.

Compacted Clay: Difficulties Obtaining Good Laboratory Permeability Tests

Testing the permeability of compacted clay is not easy. The hydraulic conductivity, k(Sr), depends upon porosity nc and degree of saturation Src after compaction, and the values reached during the permeability test, ncf and Srf. The four values are needed to predict k(Sr) using a dual-porosity model with two parameters, a and b. However, many published test reports do not give these four values. The tested clay is often unsaturated, and the measured k(Sr

Laboratory validation of a gradation design concept for sustainable applications of unbound granular materials in pavement construction

Unbound aggregates are becoming increasingly scarce and expensive due to the loss of rock quarries and gravel mines to other land uses; therefore, it is important to engineer and optimize aggregate gradations for the targeted end-performances. This paper is aimed at validating in the laboratory a newly introduced gradation design concept intended for controlling structural assembly strength (stability) and drainage characteristics (field drainability). Aggregate gradation optimizations were studied for two applications: (1) unbound permeable aggregate base (UPAB) and (2) mixing proportions of blending fine granite tailings (FGT), a typical crushed granite mining by-product that has long been considered “waste” materials, with coarse crushed granite aggregates (CCGA). To this goal, five representative gradations were first selected according to the current Minnesota DOT UPAB gradation band, and the effects of different UPAB gradation designs on the shear strength properties and particle breakage potential were investigated using a large-scale direct shear test device. In the second application, one of the common quarry byproduct wastes (i.e., FGT), were mixed with CCGA in varying percentages to explore their potential use for building pavement foundations. Both laboratory permeability and large-scale monotonic triaxial compression tests were performed to investigate the effects of blending proportions on the stress–strain behavior. Based on the test results, the optimum aggregate gradations recommended by the new gradation design concept provided enhanced stability without compromising drainability. The new gradation design concept, hence validated in this study with produced optimum gradations, is expected to achieve sustainable and beneficial unbound aggregate applications for cost-effective long-life pavements.