Well-graded Sand Research Articles

On the compression behaviour of reconstituted soils

Transitional behaviour has been recognised in a diverse range of soils in the literature to date, from gap-graded soils to well-graded silts and sands. It is typified by non-convergent compression paths and critical state lines that are non-unique and which are dependent on the initial sample density. Many soil mechanics theories assume soils to have unique normal compression and/or critical state lines, which is not the case for a transitional soil. For such a soil it would therefore be difficult to identify the effects of structure on the mechanics since there is no unique behaviour of the soil when reconstituted. This paper describes series of oedometer tests that were performed to investigate in more detail when and why non-convergent compression behaviour might be expected, as a first step to identifying which soils are transitional. The effects of mixing soils of different grain sizes and mineralogies were explored, the tests revealing that convergent or non-convergent behaviour could be brought about either by relatively small changes to the proportions of the soil particles or by changes to their nature. It was also found that in some soils with non-convergent compression behaviour there was particle breakage while in others there was not. Since the factors that influence the mode of compression behaviour were found to be complex, it is concluded that each new soil encountered must be assessed individually for whether it is transitional, and that the accuracy of void ratio measurements is of particular importance in establishing this reliably.

Characterization of mesoscale instabilities in localized granular shear using digital image correlation

Within shear bands in sands, deformation is largely non-affine, stemming primarily from buckling of well-known force chains and also from vortex-like structures. In the spirit of current trends toward multiscale modeling, understanding the links between these mesoscale deformational entities and corresponding macroscale response will form the basis for the next generation of sand behavioral models and may also aid in efforts to understand jamming–unjamming transitions in dense granular flows in general. Experimental methods to quantify and characterize such subscale kinematics, in particular in real sands, will play critical roles in these efforts. Digital Image Correlation (DIC) is a fast growing experimental technique to nondestructively measure surface displacements from digital images. Here, DIC has been employed to identify and characterize the development of vortex structures inside shear bands formed in dense sands during plane strain compression. A rigorous assessment of the DIC method has been performed, in particular for subscale behavioral characterization in unbonded granular solids, and guidelines are offered for accurate implementation. While DIC systematically overestimates shear band thickness, a methodology has been devised to compensate for this overestimation. Shear band thickness for four different uniform sands were found to range between 6 and 9 grain diameters, and for a well-graded sand between 8 and 9.5 grain diameters. These determinations agree with visual inspections of grain kinematics from the image data, as well as recent theoretical predictions.

Can Surface Overflow Rate Predict Particulate Matter Load Capture for Common Urban Drainage Appurtenances?

Urban drainage appurtenances separate particulate matter (PM) and detritus unintentionally and by design. Such PM separation impacts conveyance, treatment, and maintenance practices. This study examines two common appurtenances: Gully pots (or catch basins) and screened hydrodynamic separators (HS). Under steady and controlled physical model testing, PM separation was measured for influent granulometry [particle size distributions (PSDs), PM specific gravity]. Catch basin separation ranged from 40 to 99% for a monodisperse (well-graded sand, SW) PSD and 60 to 83% for a hetero-disperse PSD. With similar testing, a clean HS (to avoid scour dominating PM separation), the HS was also loaded with a heterodisperse sandy silt (ML) and tested as a function of flow, with separation of 40 to 65%, as compared to 70 to 99% for the SW, similar to the catch basin. Physical model results were compared to the surface overflow rate (SOR) model, illustrating that the SOR overestimated PM separation by 3–13%. The SOR was extended to unsteady runoff events. For unsteady loading of an HS with complex hydrodynamics and short residence times, the SOR overpredicted measured PM separation by 3–22% on the basis of PM granulometry. For maintenance and coarse PM load inventories, the SOR can reasonably predict the fate of coarse PM, subject to Type I settling in an HS and catch basin units with similar PM separation behavior. If suspended PM mass dominates the particle size distribution (PSD), is the focus of treatment, or for units with long residence times, the continuous phase hydrodynamics must be coupled with a discrete phase model, requiring analytical or numerical models such as computational fluid dynamics (CFD). For conditions illustrated herein, the SOR is reasonably robust.

Improving Native Soil Athletic Fields With Intercept Drain Tile Installation and Subsequent Sand Topdressing Applications

Intercept drain tile installation and subsequent sand topdressing applications can provide a built-up sand-based system. There are a number of different intercept drain tile spacing and sand layer depth recommendations. The objectives of this research were to determine the effects of intercept drain tile spacing on the surface runoff, soil water content, and surface shear strength of a compacted sandy loam with sand topdressing. A single factor, RCBD field study in East Lansing, Michigan, was seeded May 29, 2007, with a Kentucky bluegrass (Poa pratensis L.)― perennial ryegrass (Lolium perenne L.) mixture. Intercept drain tiles were spaced 2.0, 3.0, 4.0, and 6.0 m apart and were compared with an 8.1-m-long control without intercept drain tiles. Well-graded sand (90.0% sand, 7.0% silt, and 3.0% clay) was used for topdressing. After the accumulation of a 2.4-cm sand layer, simulated traffic at two applications per week was applied to all treatments using the Cady traffic simulator from October 10 to November 3, 2007. In 2008, topdressing, providing a 4.8-cm depth accumulated during a 2-year period, and traffic were repeated on the same experimental treatments. When a 2.4-cm sand layer is present, surface runoff and soil water content are generally directly related to intercept drain tile spacing, and drain tiles, spaced 2.0, 3.0, and 4.0 m apart, will provide increased surface shear strength. As topdressing depths were accumulated to a 4.8-cm sand layer depth in 2008, no differences in surface shear strength were observed regardless of drain tile spacing.

Hydro-mechanical constitutive model for unsaturated compacted bentonite–sand mixture (BSM): Laboratory tests, parameter calibrations, modifications, and applications

A bentonite–sand mixture (BSM) is one of the clay-based sealing components proposed for use in a Canadian deep geological repository (DGR) for used nuclear fuel. Numerical modelling to assess the overall design of the proposed DGR requires characterisation of the hydraulic–mechanical (H–M) of each of the components of the sealing system, including the BSM. The BSM currently under consideration is a 50/50 mixture (by dry mass) of bentonite and well-graded silica sand, compacted to a dry density of at least 1.67 Mg/m 3. This paper presents the H–M constitutive model parameters, calibrated for BSM specimens under saturated and unsaturated conditions, based on various laboratory tests. A set of parameters for an elastoplastic model for unsaturated soil, Basic Barcelona Model (BBM), have been determined to simulate the mechanical behaviour of the BSM specimen. A set of parameters for van Genuchten’s Soil–Water Characteristic Curve (SWCC) and Kozeny’s hydraulic permeability model have been determined to simulate the hydraulic behaviour of the BSM specimen. Using a finite element computer code, CODE_BRIGHT, these sets of parameters have been used to simulate H–M processes in BSM specimens during water infiltration under constant volume (CV) and constant mean stress (CMS) boundary conditions. The key features of the selected constitutive models that are different from the laboratory tests of the BSM specimen have been summarised. The functions to improve the capability of the selected constitutive models to match the laboratory test results of the BSM specimen have been proposed.

Effects of granular columns in compacted fills

Compacted fills are frequently used in engineering construction where site levels need to be raised. Increased environmental restrictions, coupled with the growing cost of virgin aggregate, have prompted more widespread reuse of site-won fill from earthworks. It is well established that the subsequent behaviour of the fill is highly related to the nature of its placement, which, if not correct, can lead to significant future difficulties. When placed, fills are generally unsaturated; however, over time they may experience an increase in water content owing to infiltration arising from rainwater, surface runoff or groundwater recharge. This saturation process can be accompanied by substantial changes in volume or reduction in shear strength; these can result in large and often non-uniform ground movements, which typically cause loss of serviceability. Previous research has indicated that such effects may be reduced through the use of ground improvement techniques such as granular columns. The work reported in this paper examines the performance of both engineered and unengineered compacted fills, prepared at four different initial moisture contents within 2% of optimum prior to saturation. Specimens were prepared by mixing kaolin and well-graded medium sand at a ratio of 1:9. Two loading conditions were considered: (a) monotonic loading and (b) static loading, during which saturation occurred. The performance of the ground improvement was examined by introducing a single 32 mm diameter granular column. In addition, the possibility of column strengthening was also considered by encasing the column in geogrid reinforcement and cement stabilisation. The results have shown that the inclusion of granular columns in unengineered cohesive fill improved the overall bearing capacity and settlement performance; however, a marginal reduction in performance was observed in the engineered fill specimens.

Ultimate Limit State of Deep-Corrugated Large-Span Box Culvert

Limit state design requires independent assessment of both load and resistance. Although much is known about the live and dead loads that may act on box culverts, there is no known measurement of the resistance (or capacity) at the ultimate limit state. The objective of this study is to present results from a full-scale experiment conducted on a buried, deep-corrugated, large-span box culvert under controlled laboratory conditions—the first conducted to its ultimate limit state. The box culvert had a 2.4-m rise and 10-m span (7.9 × 32.8 ft) and was fabricated from steel plate 6 mm thick with corrugations 150 mm deep at a 400-mm pitch (0.24 × 6 × 16 in.). The box culvert was backfilled to a minimum cover depth of 0.45 m (1.5 ft) with densely compacted well-graded sand and gravel. Tandem-axle loading was then applied by an actuator until an ultimate limit state was attained. The ultimate limit state of the box culvert involved the formation of plastic hinges at the crown and shoulders at a total applied force of 1,100 kN (250 kips). The force required to reach the ultimate limit state was 1.8 times larger than the factored design tandem-axle load from the AASHTO bridge design specifications. Similarly, the factored resistance at the ultimate limit state was 1.7 times larger than the factored CL-625-ONT tandem-axle load from the Canadian highway bridge design code.

Response of a polyvinyl chloride water pipe when transverse to an underlying pipe replaced by pipe bursting

An existing deteriorated or hydraulically undersized pipe can be replaced with a new pipe by static pipe bursting. Cavity expansion during pipe bursting induces ground movements, which may potentially damage nearby buried utilities if they are in close proximity to the pipe bursting operation. A large-scale pipe bursting experiment was performed in an 8 m long, 8 m wide, and 3 m deep test pit filled with a well-graded sand and gravel soil. A polyvinyl chloride (PVC) pipe, crossing transversely and 0.45 m above the existing pipe being replaced, was instrumented with strain gages to quantify the response of that transverse utility to the ground movements associated with pipe bursting. In this paper, the measured strain and corresponding deflection of the PVC pipe are examined and compared with measurements of surface uplift. The maximum longitudinal strain measured in the pipe was less than 0.1% and its vertical diameter decreased by only 0.5%, suggesting that ground displacements induced by pipe bursting did not jeopardize the transverse water pipe’s long-term performance, provided its joints were not damaged. A simplified design equation is introduced and shown to provide estimates of maximum longitudinal strain in the PVC pipe close to those measured during the laboratory experiment.

Ground Displacements from a Pipe-Bursting Experiment in Well-Graded Sand and Gravel

Pipe bursting is a construction technique that involves the replacement of an existing buried pipe with potentially much less surface disturbance than traditional cut and cover construction. However, excessive ground movements associated with pipe-bursting operations may lead to damage to surrounding infrastructure. A static pipe-bursting experiment was performed in sand and gravel within an 8-m-long, 8-m-wide, and 3-m-deep test pit to quantify the ground displacements from pipe bursting. An existing unreinforced concrete pipe buried 1.385 m below the ground surface was replaced with a high-density polyethylene pipe. Pulling force and the three-dimensional nature of surface displacements associated with pipe bursting are examined. The 4-m wide surface response had a peak vertical displacement of 6 mm. In addition, transverse displacements of 1.2 mm resulted in the formation of a tension crack in the ground above the concrete pipe. This experiment offers data that improves the understanding of the mechanisms of ground disturbance, and provides unique experimental data for calibration of numerical models.

Spatial time domain reflectometry and its application for the measurement of water content distributions along flat ribbon cables in a full‐scale levee model

Spatial time domain reflectometry (spatial TDR) is a new measurement method for determining water content profiles along elongated probes (transmission lines). The method is based on the inverse modeling of TDR reflectograms using an optimization algorithm. By means of using flat ribbon cables it is possible to take two independent TDR measurements from both ends of the probe, which are used to improve the spatial information content of the optimization results and to consider effects caused by electrical conductivity. The method has been used for monitoring water content distributions on a full‐scale levee model made of well‐graded clean sand. Flood simulation tests, irrigation tests, and long‐term observations were carried out on the model. The results show that spatial TDR is able to determine water content distributions with an accuracy of the spatial resolution of about ±3 cm compared to pore pressure measurements and an average deviation of ±2 vol % compared to measurements made using another independent TDR measurement system.

Three-Point Imaging Test for AASHTO Soil Classification

A rapid, digital image–based test has been developed for the classification of highway subgrade materials according to the AASHTO system. The test involves segregating particles in a sedimentation column, then determining the elevations at which 2.0-, 0.425-, and 0.075-mm grains (No. 10, No. 40, and No. 200 sieves, respectively) are found. If it is assumed that porosity variations throughout the column are insignificant, as established in previous studies, then the distances between these elevations translate to the percentages that pass through the various sieves. The method uses a previously developed calibration between an image wavelet decomposition index and the pixels per particle diameter. At a camera magnification of 32.5 pixels/mm, the entire grain size range from 2.0 to 0.075 mm is resolved. Thus, only a single fixed magnification lens is needed for the system. The accuracy of the new test is demonstrated by comparing the digital image–based results and conventional sieving for three soil specimens: well-graded sand, uniformly fine sand, and sandy silt. The advantages of the three-point imaging test for AASHTO soil classification over conventional sieving and hydrometer tests include reduced testing time, low noise, possibly lower equipment costs, and the elimination of airborne particles in the lab.

Geological and Physical Factors Affecting the Friction Angle of Compacted Sands

This study evaluated the effects of physical characteristics and geologic factors on the shear strength of compacted sands from Wisconsin that are used as granular backfill for mechanically stabilized earth walls and reinforced soil slopes. Physical properties and shear strength were determined for 30 compacted sands collected from a broad range of geological deposits. Relationships between strength/deformation behavior, geologic origin, and physical properties were used to categorize the sands into four friction angle groups. Sands with the lowest friction angle are derived from weathering of underlying sandstones, and tend to be medium-fine, well-rounded, and poorly graded sands. Sands with the highest friction angle are from recent glacial activity and tend to be coarser grained, well-graded, and/or angular sands. A multivariate regression model was developed that can be used to predict friction angle (ϕ′) of compacted sands from comparable geological origins based on effective particle size (D10), maximum dry unit weight (γdmax), and Krumbein roundness (Rs).

Effect of clay content on well-graded sands due to infiltration

This paper describes various experimental studies and numerical analyses to simulate the rainfall-induced slope failures caused by infiltration due to prolonged rainfall. The emphasis was on quantifying the effect of fine-grained contents which influence the infiltration rate of the wetting front of initially unsaturated slopes during rainfall. Suction tests using a tensiometer were performed for the wetting front suction of five mixture samples with varying fine-grained contents. Subsequently, numerical analyses for the stability of unsaturated infinite slopes were carried out for different relative densities and mixture portions based on the soil water characteristic curves obtained by a pressure plate. In the stability analyses, the interface between fully saturated- and partially saturated-zones was chosen as a relatively failure surface that develops parallel to the original slope. It is shown that the fines are highly influential on the wetting front suction of unsaturated soil slopes. Based on the results, it is found that fines affect wetting front suction up to 15% fines content, and also the wetting front suction beyond 15% fines content does not considerably influence the stability of unsaturated slopes.

Analysis of Swelling and Shrinkage Behavior of Compacted Clays

The impact of the variation in compaction condition on the swelling and shrinkage behavior of three soils has been examined. Two natural soils, namely red soil and black cotton soil, and one artificially mixed soil sample of commercial bentonite with well-graded sand, were studied. Compaction curve for Standard Proctor conditions were plotted and four compaction conditions were selected. Experimental results showed that clay mineralogy dominates over compaction conditions in influencing the swelling and shrinkage behavior of the tested soils. Monitoring of void ratio (e)−water content (w) relations during shrinkage showed that soil specimens generally shrunk in three distinct linear stages. A small reduction in void ratio occurred on reduction in water content during the first shrinkage stage and was termed as initial shrinkage. In second stage, void ratio decreased rapidly with reduction in water content and was termed as primary shrinkage. In third and final stage, reduction in water content is accompanied by a marginal change in void ratio and it’s called residual shrinkage. Irrespective of initial compaction conditions studied, the transition from primary to residual shrinkage for all the specimens occurred within a narrow range of water content (10–15%).

Scale Effects of Shallow Foundation Bearing Capacity on Granular Material

Scale effects of shallow foundation bearing capacity on granular materials were investigated to further evaluate the trend of decreasing bearing capacity factor, Nγ , with increasing footing width, B , observed by other researchers. Model-scale square and circular footing tests ranging in width from 0.025 to 0.914 m were performed on two compacted sands at three relative densities. Results of the model-scale footing tests show that the bearing capacity factor, Nγ , is dependent on the absolute width of the footing for both square and circular footings. Although this phenomenon is well known, the current study used a large range of footing sizes tested on well-graded sands to show that the previously reported modifications to the bearing capacity factor, Nγ , using grain-size and reference footing width do not sufficiently account for the scale effect seen in the test results from this study. It also shows that behavior of most model-scale footing tests cannot be directly correlated to the behavior of full...

Bearing Capacity of Square and Circular Footings on a Finite Layer of Granular Soil Underlain by a Rigid Base

Traditional bearing capacity theories for the ultimate capacity of shallow foundations assume that the thickness of the bearing stratum is infinite. The presence of a hard layer within a certain depth below the foundation can significantly influence the unit load supported by the soil. Therefore the original bearing capacity equations should be modified to account for this condition in determining the ultimate bearing capacity. In order to evaluate this phenomenon further, model square and circular footing tests were performed on a bed of well-graded sand. Test beds were prepared at three different relative densities corresponding to loose, medium, and dense conditions: Dr =24 , 57, and 87%, using five different sand layer thicknesses, H ; H∕B values of 0.5, 1, 2, 3, and 4, where B is the footing width. Results of the model scale footing tests show that the bearing capacity factor, Nγ , should be modified up to H∕B=3 , instead of H∕B=1 , as previously suggested. The footing shape factor, sγ , should accou...

The Use of Brackish and Oil-Contaminated Water in Road Construction

This paper discusses the use of non-freshwater, including brackish groundwater and oily production water, in road construction. Non-freshwater was obtained from four major oil production fields in Oman. First, chemical analyses were carried out on nine non-freshwater types, including tap water, obtained from the four sites. These water types were then used with well-graded sand (WGS), high-plasticity silt (HPS), and a road base material to evaluate water effect on material properties. Atterberg limits, compaction, California Bearing Ratio (CBR), swell percentage, swell pressure, and direct shear tests were performed. Results show that there is a slight decrease in the liquid limit when non-freshwater is used. Non-freshwater resulted in a slight decrease in optimum moisture content and a slight increase in maximum dry density in WGS, whereas with HPS it caused slight decreases in optimum moisture content and maximum dry density values. There was an increase in CBR when non-freshwater was used with WGS and HPS soils. However, the use of production water caused a decrease in CBR values for WGS. For the road base material, the use of non-freshwater generally caused a decrease in CBR. The swell pressure tends to increase when non-freshwater is used with HPS. For the road base material, there is a decrease in cohesion and an increase in friction angle when non-freshwater is used in lieu of tap water. Promising laboratory results indicate the potential use of brackish and oily water types in road construction.

Liquefaction of Clean Sand with Stratified Structure Due to Segregation of Particle Size

This study focused on the effects of stratified structure due to segregation of particle size and graded bedding in clean sand deposits on their liquefaction characteristics. A well-graded clean sand was sieved and separated into four components with different ranges of particle size, and then deposited alternatively to create stratified structure in specimens. Undrained triaxial compression tests in monotonic loading conditions and cyclic triaxial loading tests were performed on these stratified samples as well as the uniformly mixed samples of the same sand. It was observed that the liquefaction resistance of the stratified specimens was larger than the uniform specimens. These test results indicate a possibility of underestimation of liquefaction resistance of deposits with laminar structure in situ, if it is evaluated in the laboratory using homogeneously reconstituted samples.

Response of anchors to variations in displacement-based loading

The results of an experimental investigation on the effect of variations in displacement-based loading on the pullout capacity of anchors are presented. A single-pitch, screw helical anchor was used in the testing. The tests were conducted in dry, well-graded, dense, medium, and loose sands with relative densities of 79, 47, and 19%, respectively. Anchors were installed to, and tested at, shallow and deep depths. Measurements of ultimate pullout load and displacement at failure were made. The values of time-to-failure and mean loading rate were calculated and presented. The results of this study show that variations of displacement-based loading had some effect on the pullout capacity of shallow anchors but had only a slight effect on deep anchors. For a given depth of installation and a given sand state, the ultimate pullout load of an anchor decreases with increasing loading rate. This effect was more pronounced in anchors installed to shallow depths.Key words: anchors, displacement, displacement rate, pullout capacity, strain rate, sand, foundations, uplift.

PSD measurement using the single particle optical sizing (SPOS) method

A new technique for measuring the particle size distribution (PSD) of a soil, known as single particle optical sizing (SPOS), has been evaluated. A series of tests was conducted to compare the results obtained from sieve analysis and the SPOS method, using both uniform and well-graded sands of varying particle size and angularity. It was found that the SPOS method oversizes particles compared with sieving by 20–30%, as predicted by theoretical analysis. Measurements of particle size gathered from sieving and SPOS methods are not equivalent. However, as neither of the definitions of particle size implicit in each method can be considered as ‘correct’, this exercise does not represent a ‘validation’ or otherwise of the SPOS method. The repeatability of the SPOS method was demonstrated by sizing multiple samples obtained by riffling from the same batch of sand. The accuracy of the SPOS method was demonstrated by the high correlation between the calculated and measured PSD of mixed samples. Finally, a series of tests showed that the system can easily resolve a small (<1%) introduction of fine material into a coarser sample. As the technique requires only a small sample volume, it is particularly suited to the assessment of changes in PSD during geotechnical model or element testing.