Design approach for drainage layer in pavement subsurface drainage system considering unsaturated characteristics
TL;DR: In this article, an analytical model for estimating the time to drain considering the unsaturated characteristics of pavement base material and calibration of the developed model based on a mechanistic approach which is relatively inexpensive.
Abstract: Providing adequate subsurface drainage feature in a pavement system to remove the infiltrated moisture in a minimum time is an important design consideration, which prevents the premature failure of the pavement system, and hence helps in achieving a significantly lower life-cycle cost. Various surface drainage measures are taken to minimize the ingress of moisture into the pavement gradually lose their efficiency with the aging of the pavement. The use of an appropriate open-graded aggregate course as a drainage layer in the pavement is the best way to minimize the time for which the pavement materials are exposed to saturated conditions. The current drainage guidelines have been developed on the basis of moisture flow under saturated condition. A better understanding and estimation of moisture movement in a drainage layer can only be achieved by using seepage analysis that adopts the principles of saturated as well as unsaturated flow conditions. State-of-art of mathematical tools such as finite difference and FEA methods permits a rigorous solution of Richard’s equation for saturated and unsaturated moisture flow in a porous medium, the only major drawback is the need for rigorous modeling and computational tool for the simulations and the design of the drainage layer. This paper focuses on the development of an analytical model for estimating the time to drain considering the unsaturated characteristics of pavement base material and calibration of the developed model based on a mechanistic approach which is relatively inexpensive. The applicability of the approach is explained by using the four-standard aggregate gradations recommended by AASHTO for the drainage layer, as well as a dense graded aggregate layer, and the results are compared with those from the FHWA approach and finite element analysis. The study shows that the developed model performs as good as the finite element analysis, which requires rigorous numerical modeling, predicts drainage times that are significantly different from those obtained from the FHWA analysis, and that it is sensitive to key significant design parameters. Hence, the proposed model is recommended for regular use for the design of the drainage layer and for a parametric study of the complete drainage process.
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01 Dec 2020
TL;DR: In this paper, a simulation model for predicting pavement alignment is proposed to obtain the water distribution influenced by pavement alignment design under the current situation of highway reconstruction and extension in China, and the simulation model is used for predicting pave...
Abstract: To obtain the water distribution influenced by pavement alignment design under the current situation of highway reconstruction and extension in China, a simulation model for predicting pave...
4 citations
TL;DR: In this article, the authors show that pavement materials are prone to damage due to mechanical loadings and rainfall infiltration, and the rainfall initiates moisture movement within the layers and accelerates the damaging rate.
Abstract: Pavement materials are prone to damage due to mechanical loadings and rainfall infiltration. The rainfall initiates moisture movement within the layers and accelerates the damaging rate. A ...
3 citations
TL;DR: A thorough evaluation of the methods employed in previous studies and research on rainfall forecasting models was undertaken in this paper, where the effect resulting from climate change on structures of drainage infrastructure is considered in addition to the methods to enhance drainage system challenges with recent models developed for advanced drainage and waterway requirements that need to be designed in consideration of climate change.
Abstract: The atmospheric temperature globally has risen during the last few centuries, causing global warming and climate dynamics. The impact of global warming has caused environmental effects that include increased rainfall intensity, which is recognised as the leading cause of flooding, and destruction and devastation to the surrounding environment, infrastructure, and human life. Road stormwater drainage systems are used for removing and controlling excess runoff water to the right way. However, regardless of enhanced technologies, the reliability of drainage system schemes remains a major undertaking for water and hydraulic engineers alike. In this study, a thorough evaluation of the methods employed in previous studies and research on rainfall forecasting models was undertaken. Further to that, the effect resulting from climate change on structures of drainage infrastructure is considered in addition to the methods to enhance drainage system challenges with recent models developed for advanced drainage and waterway requirements that need to be designed in consideration of climate change.
2 citations
TL;DR: In this article, the effects of relative humidity and total suction condition during curing on small-strain shear modulus of a cement-treated silty sand using free-free resonant frequency tests (FFR) were determined on samples cured at different suctions corresponding to three values of 7, 75, and 100.
Abstract: This study investigated the effects of relative humidity (
$$R_{h}$$
) or total suction condition during curing on small-strain shear modulus (G0) of a cement-treated silty sand using free-free resonant frequency tests (FFR). The moduli were determined on samples cured at different suctions corresponding to three $$R_{h}$$
values of 7%, 75%, and 100%, in both unsoaked and soaked conditions. Soil–water retention curves (SWRCs), and unconfined compression strength (UCS) were also determined along with x-ray diffraction (XRD) analysis. The cement-treated SWRCs showed a much flatter slope than the non-treated ones, and the air-entry suction increased with cement content. The values of G0 increased with cement content and curing time. The highest modulus was achieved in 75%
$$R_{h}$$
curing condition. The 7%
$$R_{h} $$
condition resulted in a significant drop in modulus, even close to the non-treated G0 for the 2% cement case. At the same UCS value, the soaked cement-treated samples had higher modulus than the non-treated ones in the unsoaked condition, indicating that the effect of suction on modulus was smaller than the effect of cementation. XRD analysis revealed a greater availability of C3S in 7%
$$R_{h}$$
curing condition at 7-day curing period suggesting that the hydration process was still not complete, which explained the decrease in G0 in this curing condition.
2 citations
Cites background from "Design approach for drainage layer ..."
...…soil during curing may vary widely due to climatic and thermal factors especially for those located in the vadose zone, such as cementtreated pavement layers, platform for deep mixing, stabilized slope surface, etc., (e.g. Teltayev and Suppes 2019; Han et al. 2018; Shubham et al. 2019)....
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TL;DR: In this article , a selective literature review was conducted to demonstrate subgrade moisture variation and pavement drainage methods and their effectiveness can facilitate pavement drainage design, which will facilitate the development of sustainable pavement drainage systems.
Abstract: Drainage has been commonly employed in pavement structures to intercept water from entering pavement or to lower the water table to control the moisture content on distinct road layers. A comprehensive understanding of drainage methods and their effectiveness can facilitate pavement drainage design. Thus, a selective literature review was conducted to demonstrate subgrade moisture variation and pavement drainage methods. The subgrade moisture variation was evaluated based on previous studies from three aspects: field investigation, drainage simulation and laboratory studies. Subsurface drainage methods were summarized and some examples were demonstrated. Drainage effectiveness and its influencing factors were analysed to clarify their hydraulic and mechanical effectiveness. Research implications were proposed to provide a reference for further studies. This study aims to improve the knowledge of pavement drainage and provide a reference for sustainable drainage design. Thus, this will facilitate the development of sustainable pavement drainage systems.
1 citations
References
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TL;DR: Van Genuchten et al. as mentioned in this paper proposed a closed-form analytical expression for predicting the hydraulic conductivity of unsaturated soils based on the Mualem theory, which can be used to predict the unsaturated hydraulic flow and mass transport in unsaturated zone.
Abstract: A new and relatively simple equation for the soil-water content-pressure head curve, 8(h), is described in this paper. The particular form of the equation enables one to derive closedform analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for Kr(h) contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil-water retention curve at low water contents is important for an accurate prediction of the unsaturated hydraulic conductivity. Additional Index Words: soil-water diffusivity, soil-water retention curve. van Genuchten, M. Th. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:892-898. T USE OF NUMERICAL MODELS for simulating fluid flow and mass transport in the unsaturated zone has become increasingly popular the last few years. Recent literature indeed demonstrates that much effort is put into the development of such models (Reeves and Duguid, 1975; Segol, 1976; Vauclin et al., 1979). Unfortunately, it appears that the ability to fully characterize the simulated system has not kept pace with the numerical and modeling expertise. Probably the single most important factor limiting the successful application of unsaturated flow theory to actual field problems is the lack of information regarding the parameters entering the governing transfer equations. Reliable estimates of the unsaturated hydraulic conductivity are especially difficult to obtain, partly because of its extensive variability in the field, and partly because measuring this parameter is time-consuming and expensive. Several investigators have, for these reasons, used models for calculating the unsaturated conductivity from the more easily measured soil-water retention curve. Very popular among these models has been the Millington-Quirk method (Millington and Quirk, 1961), various forms of which have been applied with some success in a number of studies (cf. Jackson et al., 1965; Jackson, 1972; Green and Corey, 1971; Bruce, 1972). Unfortunately, this method has the disadvantage of producing tabular results which, for example when applied to nonhomogeneous soils in multidimensional unsaturated flow models, are quite tedious to use. Closed-form analytical expressions for predicting 1 Contribution from the U. S. Salinity Laboratory, AR-SEA, USDA, Riverside, CA 92501. Received 29 June 1979. Approved 19 May I960. 'Soil Scientist, Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521. The author is located at the U. S. Salinity Lab., 4500 Glenwood Dr., Riverside, CA 92502. the unsaturated hydraulic conductivity have also been developed. For example, Brooks and Corey (1964) and Jeppson (1974) each used an analytical expression for the conductivity based on the Burdine theory (Burdine, 1953). Brooks and Corey (1964, 1966) obtained fairly accurate predictions with their equations, even though a discontinuity is present in the slope of both the soil-water retention curve and the unsaturated hydraulic conductivity curve at some negative value of the pressure head (this point is often referred to as the bubbling pressure). Such a discontinuity sometimes prevents rapid convergence in numerical saturated-unsaturated flow problems. It also appears that predictions based on the Brooks and Corey equations are somewhat less accurate than those obtained with various forms of the (modified) Millington-Quirk method. Recently Mualem (1976a) derived a new model for predicting the hydraulic conductivity from knowledge of the soil-water retention curve and the conductivity at saturation. Mualem's derivation leads to a simple integral formula for the unsaturated hydraulic conductivity which enables one to derive closed-form analytical expressions, provided suitable equations for the soil-water retention curves are available. It is the purpose of this paper to derive such expressions using an equation for the soil-water retention curve which is both continuous and has a continuous slope. The resulting conductivity models generally contain three independent parameters which may be obtained by matching the proposed soil-water retention curve to experimental data. Results obtained with the closedform equations based on the Mualem theory will be compared with observed data for a few soils having widely varying hydraulic properties. THEORETICAL Equations Based on Mualem's Model The following equation was derived by Mualem (1976a) for predicting the relative hydraulic conductivity (Kr) from knowledge of the soil-water retention curve
22,781 citations
TL;DR: In this paper, a nonlinear, least squares computer program is used to determine the best-fit parameters for experimental data presented in the literature, based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution.
Abstract: The soil-water characteristic curve can be used to estimate various parameters used to describe unsaturated soil behaviour. A general equation for the soil-water characteristic curve is proposed. A nonlinear, least-squares computer program is used to determine the best-fit parameters for experimental data presented in the literature. The equation is based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution of the soil (i.e., the desaturation is a function of the pore-size distribution). The equation has the form of an integrated frequency distribution curve. The equation provides a good fit for sand, silt, and clay soils over the entire suction range from 0 to 106 kPa. Key words : soil-water characteristic curve, pore-size distribution, nonlinear curve fitting, soil suction, water content.
2,644 citations
TL;DR: Gardner as mentioned in this paper describes some STEADY-state solutions of the UNSATURATED MOISTURE FLOW EQUATION with application to EVAPORATION from a WATER TABLE.
Abstract: SOME STEADY-STATE SOLUTIONS OF THE UNSATURATED MOISTURE FLOW EQUATION WITH APPLICATION TO EVAPORATION FROM A WATER TABLE W. GARDNER; Soil Science
2,346 citations
1,007 citations
TL;DR: The coefficient of permeability for unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve as mentioned in this paper.
Abstract: The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general eq...
864 citations