Use of Expanded Shale Amendment to Enhance Drainage Properties of Clays

Abstract

Fine grained soils, in particular clays of high plasticity, are known to have very low values of hydraulic conductivity. Coarse aggregates have been used as a common fill material with fine grained soils for increasing the permeability of clayey soils. Expanded shale has recently been used as an amendment with clay soils to improve its drainage properties. However, limited effort has been made to quantify the effect of expanded shale on the hydraulic conductivity of clayey soils. Therefore, this paper presents the results of a series of laboratory fixed-wall permeameter tests conducted on naturally occurring clay deposits in the Austin, Texas area with different plasticity. The testing program comprised of clay samples with different quantities of expanded shale aggregates by volume, ranging between 0% and 50%, and compacted at two different compaction efforts (60% and 100% of the standard proctor compaction effort). The laboratory hydraulic conductivity of the amended Taylor clay compacted with 60% of the standard proctor effort increased by more than one order of magnitude with 20% expanded shale (by volume), more than two orders of magnitude with 30% expanded shale, and more than three orders of magnitude with 40% expanded shale. In addition to enhancing the drainage properties of the test specimen, the addition of expanded shale decreased the density of the clay samples which may benefit vegetation growth and root development. Another set of experiments conducted on Taylor Clay using limestone as amendment indicated similar effect on the hydraulic conductivity of the clay but led to increase in the density of the clay sample. The results discussed in this paper are being used in city of Austin to develop recommendations for increasing infiltration capacity of stormwater treatment systems by amending clayey soils with expanded shale material.

Hydraulic conductivity variation in compacted bentonite–fly ash mixes under constant-volume and free-swelling flow conditions

“…It can be observed that the k eq decreases from 8.7 x 10 -9 to 3.8 x 10 -12 m/s with a corresponding increase in PI from 30 % to 130 %. This trend is consistent with the previous studies (Benson et al 1994;Benson and Trust 1995;Phani Kumar and Sharma 2004;Pal and Ghosh 2013;Mechleb et al 2014). Only a marginal decrement from 3.8 x 10 -12 to 1.9 x 10 -12 m/s was noted for further increase in PI from 130 to 253.…”

“…(5) 𝑘 𝑒𝑞 = 0.00024𝑃𝐼 -3.55 Previous researchers have developed several correlations to predict k with the plasticity index (Mechleb et al 2014;Dolinar 2009;Zeng et al 2020). However, most of the correlations are based on natural soils or clay with relatively low plasticity with duration of measurements < 10 days.…”

Application of generalized boundary conditions for homogenization of thermal and filtration properties of soils

“…Solutions 𝛿𝛿 of the problem defined by equations ( 9), (10), and (11) have to belong to the Sobolev functional space 𝐻𝐻 1 (𝜔𝜔) of differentiable functions (at least once). This is ensured by the piece-wise polynomial base functions used in standard FEM discretization.…”

“…Isotropy of the constituents is assumed in this example. Clay permeability is given by 𝑘𝑘 𝑚𝑚 = 6.5e−9 m s , expanded shale permeability is given by 𝑘𝑘 𝑠𝑠 = 8e−5 m s and the permeability of interface 𝑘𝑘 𝑡𝑡 is variable in this example, ranging from 6.5e−9 m s to 8e−3 m s [11]. The size of grains was taken as 𝑑𝑑 = 0.005 m, and the expected grain volume ratio was taken as 20.5%.…”