**1. Introduction**

Desiccation heave and shrinkage characteristics of expansive soils have limited their application as a subbase for roadway pavements material in arid and semiarid climates. Randomly oriented fibers are often used to reduce the problems associated with clayey soils. The cost-effectiveness and chemical inertness of the fibers makes them useful as a soil additive [1,2]. To develop the bonding between soil grains, researchers used chemical stabilizers such as lime, cement, EICP, MICP, biopolymer, etc., in combination with fiber to improve the geotechnical properties [3–6]. The addition of fiber to the soil increases shear strength [7], reduces swelling [8,9], reduces desiccation cracking [10], and increases hydraulic conductivity (k) values [11,12]. Although fiber inclusion reduces the desiccation cracking, an increase in k values of soil limited its application in the subbase for the construction of pavements. However, the resultant properties of fiber-reinforced soil depend on the fiber type, dosage, and aspect ratio [13]. Experimental investigations on medium plasticity clay with polypropylene fiber (at 2%) inclusion results in an increase in k values by 10−<sup>3</sup> cm/s compared to untreated clay. The fiber dosage up to 0.5% resulted in acceptable hydraulic conductivity values [12]. On the contrary, k values of lime-amended high-plastic clay reduced by 10−<sup>2</sup> cm/s with a fiber dosage of 0.2% and length of 6 mm at the end of a

**Citation:** Shaker, A.A.; Al-Shamrani, M.A.; Moghal, A.A.B.; Vydehi, K.V. Effect of Confining Conditions on the Hydraulic Conductivity Behavior of Fiber-Reinforced Lime Blended Semiarid Soil. *Materials* **2021**, *14*, 3120. https://doi.org/10.3390/ma14113120

Academic Editors: Krzysztof Schabowicz and Zbyšek Pavlík

Received: 21 April 2021 Accepted: 2 June 2021 Published: 6 June 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

28-day curing period compared to specimens without curing [14]. To meet the requirements of hydraulic conductivity values for lime-stabilized high-plastic clay reinforced with fiber, an optimum length of 10.5 mm with 0.5% dosage for a 15-day curing period is proposed using the response surface method [15]. On the other hand, few researchers have studied the effect of lime on the hydraulic conductivity of soils. The results showed an increase in the hydraulic conductivity with lime [16–18]. In addition, the k value of lime-treated soil increased at initial curing periods and then decreased at higher curing periods [19,20]. Earlier research concentrated on evaluating the hydraulic conductivity of fiber-reinforced soil using a conventional rigid wall permeameter (RWP).

However, for a compacted clay as a subgrade layer, the surcharge load coming on it plays a major role in controlling the hydraulic conductivity values. According to Daniel et al. [21], complete control over imposed stress on the soil is not possible, resulting in the inability of RWP to measure vertical and horizontal deformations. To overcome these limitations, a flexible wall permeameter (FWP) was introduced, in which back pressure saturation and the minimization of sidewall leakages facilitate in determining the accurate value of saturated hydraulic conductivity values (ksat) [22]. Therefore, to simulate the real field conditions, researchers proposed using FWP to evaluate ksat values. Experimental investigations on sand–Alqatif clay mixture revealed that ksat values reduced with an increase in confining pressure [23]. The generalized mechanism proposed for the reduction of ksat values using FWP is that an increase in confining pressure reduces the effective pore spaces, and an increase in unit weight leads to a reduction of effective flow paths.

There are limited studies on the evaluation of ksat values for fiber-reinforced soil using FWP. In lieu of this, the present research evaluates the ksat values of a lime-stabilized Al-Ghat soil with fiber inclusion using FWP. The effect of dosage, length of the fiber, and curing period are considered in evaluating the ksat values. Then, the values obtained from the study are compared with the values in the literature [13] to evaluate the effectiveness of FWP in the accurate measurement of ksat values.

#### **2. Materials**

#### *2.1. Soil*

Locally available natural soil sourced from Al Ghat (26◦1- 36-- N, 44◦57- 39-- E) town, Riyadh Province, Saudi Arabia, was selected for the present study. Disturbed samples were obtained from open test pits excavated to a depth of 1.5–3.0 m below the ground surface. The physical characterization of soil (carried out in accordance with relevant ASTM standards) seen from Table 1 reveals that the selected soil is a high plastic clay (CH) as per the Unified Soil Classification System (USCS), and it is expansive in nature [13].

**Table 1.** Physical properties of studied soil.

