Geotechnical Instabilities in Road Embankments: Analysis of a Landslide in Schistose Road Cut-and-Fill on the Taza-Al Hoceima Expressway, Northern Morocco

Abstract

This article delves into the vital issue of geotechnical stability in road embankments, a crucial element for the integrity of road infrastructures and the safety of its users. It focuses on a specific case of landslide along the Taza-Al-Hoceima highway at kilometer point 67+800. This case is particularly significant due to the embankment's composition, which predominantly consists of schistose cut and fill, in addition to the topographic and hydrographic complexity of the area. The main ambition of this study is to delineate the various factors and underlying mechanisms that precipitate such geotechnical instabilities. To this end, the research integrates field investigations with laboratory analyses. A major aspect of this research involves examining the characteristics of the schists at the site. These schists are identified as fragmentable clayey rocks (R34), demonstrating a range of Micro-Deval (MDE) coefficients between 67 to 100 and Los Angeles (LA) coefficients from 33 to 57. Upon alteration, these schists are reclassified as fine soils (A2), consisting of 35-40% fine particulate matter, with plasticity indices ranging from 13 to 22 and a high permeability rate (Kp=10-3 m/s). The study underscores the schists' vulnerability, particularly their susceptibility to evolutionary changes and water sensitivity. It also reveals that local geomorphological and hydrodynamic conditions exacerbate water infiltration. Heavy rainfall is pinpointed as the trigger for the landslide incident. Although the current road drainage system effectively manages surface water, the findings of the analysis emphasize the critical need to enhance this system to address the significant water infiltration problem identified.

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Iraqi Geological Journal
Akoudad et al.
2024, 57 (2B), 256-271
Iraqi Geological Journal
Journal homepage: https://www.igj-iraq.org
DOI: 10.46717/igj.57.2B.17ms-2024-8-27
256
Geotechnical Instabilities in Road Embankments: Analysis of a Landslide in
Schistose Road Cut-and-Fill on the Taza-Al Hoceima Expressway, Northern
Morocco
Amine Akoudad1*, Kaoutar Bargach2, Hicham El Asmi3, Ahmed Zian4, Aziz Hayati3, Ibrahim Darkik5,
Mostafa El Qandil1
1
Laboratory of Electrochemistry Modeling and Environment Engineering, Department of chemistry, Faculty of
Sciences Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, Fez, Morocco.
2
Geo-Biodiversity and Natural Patrimony Laboratory (GeoBio), Geophysics, Natural Patrimony Research Center
(GEOPAC), Institut Scientifique, Mohammed V University in Rabat, Morocco.
3
Laboratory of Geosciences, Environment and Associated Resources, Department of geology, Faculty of
Sciences Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, Fez, Morocco
4
Laboratory of Engineering Sciences and Applications, Department of Civil Engineering, Water and
Environment, Energy and Renewable Energy, National School of Applied Sciences of Al Hoceima,
Abdelmalek Essaadi University, Morocco
5
Laboratory of Societies, Territories, History and patrimony, Department of Geography, Faculty of Letters and
Human Sciences, Mohamed V University, Rabat, Morocco.
*
Correspondence: amine.akoudad@usmba.ac.ma
Abstract
Received:
28 November 2023
This article delves into the vital issue of geotechnical stability in road embankments, a
crucial element for the integrity of road infrastructures and the safety of its users. It
focuses on a specific case of landslide along the Taza-Al-Hoceima highway at kilometer
point 67+800. This case is particularly significant due to the embankment's composition,
which predominantly consists of schistose cut and fill, in addition to the topographic and
hydrographic complexity of the area. The main ambition of this study is to delineate the
various factors and underlying mechanisms that precipitate such geotechnical instabilities.
To this end, the research integrates field investigations with laboratory analyses. A major
aspect of this research involves examining the characteristics of the schists at the site.
These schists are identified as fragmentable clayey rocks (R34), demonstrating a range of
Micro-Deval (MDE) coefficients between 67 to 100 and Los Angeles (LA) coefficients
from 33 to 57. Upon alteration, these schists are reclassified as fine soils (A2), consisting
of 35-40% fine particulate matter, with plasticity indices ranging from 13 to 22 and a high
permeability rate (Kp=10-3 m/s). The study underscores the schists' vulnerability,
particularly their susceptibility to evolutionary changes and water sensitivity. It also
reveals that local geomorphological and hydrodynamic conditions exacerbate water
infiltration. Heavy rainfall is pinpointed as the trigger for the landslide incident. Although
the current road drainage system effectively manages surface water, the findings of the
analysis emphasize the critical need to enhance this system to address the significant water
infiltration problem identified.
Accepted:
23 May 2024
Published:
31 August 2024
Keywords:
Schists; Backfill; Road embankments; Geomorphology; Road drainage
system; Runoff water; Geotechnical instability; Atterberg limits,
Permeability testing, Micro-Deval, Los Angeles.

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1. Introduction
Road infrastructures crossing hilly terrain require the installation of road embankments. Despite their
critical role, these embankments pose significant geotechnical stability challenges. Landslides represent
a primary consequence of such instability, with the potential to cause considerable disruptions in traffic
flow and, under severe circumstances, catastrophic outcomes (Yazidi et al., 2017; Tsoata, 2020;
Sissakian et al., 2021; Al-Samarrai, 2022).
A landslide is characterized by the movement of soil or materials along a pre-existing failure surface
(Silva and Zuquette, 2013). This phenomenon is influenced by various factors, including mechanical
stresses due to road loads (Slimi, 2010), dynamic perturbations such as earthquakes (Jeandet, 2018;
Alamanis and Dakoulas, 2019), or meteorological events, like heavy rainfall (Femmam, 2014; Kirat,
2016), the latter being a primary contributor to roadway instability identified in this investigation.
Moreover, the influence of geomorphological features (Fressard, 2013, Ezzardi et al., 2015; Al-Dhahi
and al., 2023), alongside geotechnical attributes such as geometry, lithology and soil characteristics
(Bissaya et al., 2014; Nguyen, 2015; Abidi and al., 2019; Qader, 2020, Akoudad et al., 2024) is critical
in dictating landslide susceptibility. Despite progress in understanding these complex mechanisms,
pinpointing precise causative factors continues to pose a challenge. Against this backdrop of uncertainty,
persisting with research endeavors is essential to refine our capacity for predicting, managing, and
mitigating the risks associated with landslides.
This article centers on a particular landslide event that occurred in northern Morocco, precisely at
kilometer point 67+800 along the newly constructed expressway connecting Taza with Al Hoceima (Fig.
1). Recent investigations have underscored the elevated landslide susceptibility of this area, covering a
probability of 42.47% across the overall area, and rising to 80% in our study sector (Cherifi et al.,
2022b). This sector is distinguished by its remarkably complex topography and hydrography. From a
geotechnical standpoint, the embankment under scrutiny, extending 11 meters in height, is mainly
composed of schists, incorporating both cut and fill configurations.
The primary aim of our study is to deepen the understanding of the factors and mechanisms
triggering landslides in embankments. Our specific objectives include: i) lithological, mineralogical and
geotechnical characterization of the schists in the study area, and evaluate their influence on the noted
instability; ii) exploration of the correlation between the embankment's geographical positioning and its
instability risk; iv) examination of the impact of water on instability dynamics; v) decipher the
mechanisms triggering the landslide occurrence, and pinpointing the principal contributing factor.
This study will highlight the essential requirement for meticulous attention to the geotechnical
characteristics of schist, as well as the geomorphological and hydrological specifics of the area, during
the road design process. Acknowledging these elements is key to mitigating the potential for instability
in road embankments.
2. Study Area
The study sector is located within the Aknoul commune, part of the Taza Province. It is positioned
to the northeast of the city of Taza (Fig.1). This sector is situated in the southern portion of the External
Rif, encompassing the Aknoul nappe (Fig. 2). The nappe extends from Boured to Aknoul and is
comprised of allochthonous materials. Stratigraphically, it reveals shales and sandstones at the base,
which give way to blackish Cretaceous marls and pélites. This formation is topped by white Eocene-
Oligocene marly limestones, culminating in the Numidian sandstone of the Aquitanian (Poujol, 2014).
These rock formations are often characterized by their softness (Homonnay, 2019). The region
experiences a semi-arid climate with Mediterranean influences, with temperature variations from 3°C
to 34°C and annual precipitation levels ranging from 300 to 450 mm.

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Fig.1. Geographic location of the occurred landslide
Fig. 2. Structural map of the Rif Belt, after suter (1980 a,1980b) and Chalouan et al. (2001), modifed. Alboran basin
after chalouan et al. (1997) and Comas et al. (1999). Gharb and Atlantic margin after Flinch (1996)
3. Materials and Methods
To achieve a better understanding of the factors and mechanisms responsible for the observed
instability, we opted for a combined approach, associating field investigations and laboratory analyses.

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During our on-site investigations, we prioritized reconnaissance and assessment of the instability
and its related disturbances. Additionally, an analysis of the embankment and its adjacent areas was
conducted. Field observations were instrumental in the creation of a block diagram, which effectively
illustrated the site morphology, capturing the changes before and after the construction of the road, and
emphasized the relative position of the embankment under study. We also carefully sampled both altered
and compacted schist, as well as sandstone limestone. These samples, taken from the embankment and
nearby outcrops, ensure that the various geological formations in the area are representative.
Subsequently, we analyzed the collected samples in the “LABOCONTROL” laboratory to assess their
geotechnical properties. The samples of compacted schist and sandstone limestone were assessed using
Micro-Deval (MDE) and Los Angeles (LA) tests. These tests are crucial for characterizing the
mechanical strength and wear of rock materials. Concurrently, samples of altered schist, were subjected
to standard identification tests, including granulometric analysis and Atterberg limits tests, to determine
their granulometric distribution and plasticity properties. Additionally, permeability tests were
conducted on altered schists utilizing a constant load permeameter equipped with two piezometers,
enabling the measurement of the volume of water passing through the sample. On the mineralogical
front, altered schists underwent a comprehensive characterization process using X-ray diffraction
(XRD) analysis, using a Panalytical X'Pert PRO powder diffractometer equipped with an X'Celerator
ultrafast scintillation detector.
Based on the results obtained, we used the Moroccan guide of road earthworks (GMTR, 2011) to
classify the samples tested. This approach enabled us to clarify the characterization of the formations in
place, anticipate their behavior and suggest guidelines for their possible reuse as embankments. We also
incorporated pre-existing data from geotechnical surveys, carried out by the “Provincial Department of
Equipment and Water of Taza”, into our analysis. This involved a meticulous analysis of the
topographical profile of the embankment, as well as the study of data from three boreholes (B1, B2 et
B3), each reaching a depth of 15 meters. This information was instrumental in the development of an
accurate geotechnical profile for the embankment under study.
Table.1. GPS Coordinates of Borehole Locations (B1, B2, and B3).
Borehole Number
GPS Coordinates (Latitude, Longitude)
B1
B2
B3
34°43'17.05"N, 3°49'49.98"W
34°43'16.80"N, 3°49'50.28"W
34°43'16.60"N, 3°49'50.51"W
4. History and Description of the Instability
Approximately three years following the completion of the road construction, a significant section
of the roadway on the route towards Al Hoceima, spanning around 20 meters in length and 1,80 meters
in width, exhibited evident geotechnical instability. Pathologies observed within this section included
longitudinal and transversal fissures, some extending over metric scales, as well as subsidence with
disparities quantifiable on a centimeter scale. Despite multiple corrective interventions, primarily
through the addition of extra layers of asphalt, the recurrence of these pathologies was noted. The most
severe incident occurred on the night of April 6, 2022, characterized by heavy rainfall. On-site
assessments have demonstrated that this event involved a landslide on the slope adjacent to the above
section. This landslide was characterized by a downward movement of materials, a clearly
distinguishable detachment niche with a depth of up to two meters, and a curved surface rupture
morphology (Fig. 3. a and b). Such features align with the characteristics of rotational landslides. The
pronounced inclination of a tree on the slope was a prominent visual indicator of both the direction and

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magnitude of the landslide (Fig. 3. b). This landslide led to a substantial collapse that impacted almost
half of the roadway, resulted in the deterioration of the concrete berm, and compromised the stability of
the safety barrier (Fig. 3. b and Fig. 4).
Fig. 3. Field photos from two different angles depicting landslides. (a): highlights the detachment niche, along
with damage to the berm and safety barrier. (b): highlights the inclination and the falling of the tree, showcasing
the slope failure. White dashes: initial location of the tree prior to sliding. Red dashes: Final position of the tree
after sliding.
Therefore, in order to avoid aggravating the situation, immediate action have been taken, involving
the creation of a new temporary concrete barrier to divert run-off away from the affected section (Fig.
4). Furthermore, subsequent field investigations were conducted, including reconnaissance boreholes,
lithological and topographical surveys, etc., leading to the initiation of technical studies. Ultimately, a
long-term stabilization strategy was decided upon, notably involving the reinforcement of the slope
through the construction of a reinforced concrete retaining wall, the reconfiguration of the slope by
creating terraces, the use of granular and frictional materials for backfill, and the incorporation of
geotextiles. Currently, in February 2024, this approach is in the phase of implementation.
Fig. 4. Overview of the roadway post-landslide, illustrating the collapse that affected nearly half of the roadway
and the installation of a concrete containment system

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5. Results
5.1. Lithological and Mineralogical Analysis
5.1.1. Lithology
Following fieldwork, lithological analysis reveals a notable predominance of schist formations in
the studied area. At the surface, these geological formations appear altered, but they become compact
and affected by deep-seated fracturing. Boreholes B1, B2, and B3, substantiate these observations.
Positioned along a linear axis, these boreholes conducted at various levels: on the roadway, on the slope,
and at its base. The precision of the results obtained from these boreholes has facilitated a thorough
analysis of the lithology of the slope in question.
The examination of the borehole logs (Fig. 5) identifies a schist backfill stratum positioned
immediately beneath the road infrastructure, with the total thickness of these two layers totaling 2.00
meters. It is crucial to acknowledge that this backfill originates from locally procured compact schist
fragments, allocated to the GMTR category R34. Subsequent examination of the logs uncovers layer of
altered schist, with thicknesses ranging from 5.50 to 10 meters. Embedded within this layer is a distinct
passage of sandstone limestone, singularly detected in borehole B1. A more profound exploration via
the boreholes exposes compact schist formations that extend to the deepest levels explored (15 meters).
An essential observation to underscore is the detection of water flow within the altered schist layers,
signifying pronounced hydrogeological dynamics
Fig. 5. Borehole logs of B1, B2, and B3, sourced from P.D.E.W., Taza, 2022, with locations in Table 1.
5.1.2. Mineralogy
X-ray diffraction (XRD) analysis conducted on four schist samples; Fig. 6 uncovers a diverse
mineralogical composition. The spectra predominantly show notable quartz (Qz) presence, evidenced

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by pronounced peaks, mainly in the 2-theta ranges between 20° and 30°. Calcite (C) also prominently
features across all samples, as suggested by significant peaks. While dolomite (D) and ankerite (A) are
less prevalent, they are identifiable through their distinct peaks. The detection of manganese oxide (Mo)
is also noted by minor peaks. The presence of manganese oxides and ankerite is indicative of chemical
interaction with water (Ahmat et al., 2022). Moreover, the detection of calcite and dolomite, minerals
renowned for their susceptibility to dissolution (Eppner, 2016), highlights the vulnerability of these
schists to structural compromise. These findings emphasize the significant role of water-mineral
interactions in the deterioration of the embankment's integrity.
Fig. 6. XRD of the schist samples (E1, E2, E4, and E5) procured from the investigated slope
5.2. Evaluation and Analysis of Geotechnical Soil Properties
5.2.1. Permeability
The lithology of the sector, ranging from altered schist at the top to compact schist at depth, has a
significant influence on permeability. Laboratory permeability tests conducted on samples of altered
schist demonstrated high permeability, exhibiting an average permeability coefficient in the order of
Kp=10-3 m/s. As for the compact schists, although the means available do not allow their direct
evaluation, their fracturing makes them permeable, but their dense, low-porosity structure indicates a
significantly low permeability, particularly in comparison with the altered schists. These results suggest
that the altered schist layers are the preferred zones for water circulation in the sector.
5.2.2. Physical and mechanical properties
The compacted schists revealed significant disparities in terms of resilience and hardness,
underlining their heterogeneity. Indeed, the values observed for Micro-Deval (MDE) coefficients range
from 67 to 100 %, while Los Angeles coefficients vary from 33 to 57 % (Table 2). According to the
Moroccan guide of road earthworks (GMTR), this range of values classifies them in the R34 category,
attributed to the fragmentable argillaceous rock family. This classification is attributable to their intrinsic

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fragility, inducing major modifications in their geotechnical properties, including granulometric
alterations and increased plasticity, manifested by the liberation of fine particles. Consequently, the
evolutionary nature of these schists indicates a marked tendency towards instability. As a result, and in
line with GMTR recommendations, it is imperative to carefully examine the applicability of these rocks,
particularly in the construction of embankments, a central aspect of our case study. In comparison,
sandstone limestone revealed MDE coefficients between 22 and 30 %, and Los Angeles coefficients
oscillating between 16 and 20 % (Table 2). These parameters qualify it for category R21 (GMTR, 2011),
illustrating its high degree of hardness. This increased hardness justifies its unconditional use as a
backfill material, in line with GMTR recommendations. These points to the widespread applicability of
sand-lime in geotechnical engineering scenarios, offering a viable and resilient solution for various road
construction applications.
Table 2. Results of geotechnical tests for rock formations (Compact schists and sandstone limestone)
Formation
Sample No.
LA (%)
MDE (%)
GMTR class
Compact
schists
S1
57
100
R34
S2
33
68
R34
S3
36
67
R34
S4
35
99
R34
S5
39
96
R34
Sandstone
limestone
S6
21
18
R21
S7
22
16
R21
S8
25
19
R21
As for altered schists, test results (Table 3) show a percentage of particles under 0.08mm ranging
from 35% to 40%, and those under 2mm from 57% to 80%. The maximum particle size observed in all
samples does not exceed 50mm. Such findings delineate a soil texture profile that is primarily fine-
grained, yet demonstrates notable variability in soil composition. Atterberg limit assays refine the
determination of the soil's plasticity characteristics, exhibiting liquid limit (LL) values from 28% to
38%, and plasticity indices (PI) spanning 13 to 22%. In reference to the GMTR classification, these
schists are identified as fine soils, categorized precisely as class A2. While the GMTR indicates that soils
within this category are generally suitable for use as backfill material, evidenced by the positioning of
the samples relative to line A on the PI-LL discriminant diagram (Fig. 7), warrants careful consideration.
This is especially pertinent in scenarios where engineering requirements demand enhanced stability and
the soil is prone to saturation, because the plastic nature of the soil can markedly affect its volume change
behavior.
Table 3. Results of geotechnical tests on soil formations (Altered schist)
Nature
of soil
Sample
No.
Granularity
Atterberg limits
GMTR
class
%<0,08mm
%<2mm
Dmax
LL (%)
PI (%)
Altered
schists
S1
40
80
<50
38
22
A2
S2
35
57
<50
28
13
A2

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Fig. 7. IP-LL discriminant diagram showing the positioning of altered schist samples (S1 and S2) relative to line
A
5.3. Analysis of Environmental Influence
The block diagram presented in Fig. 8, illustrates the location of the slid embankment, and provides
an intricate representation of the site's morphology. With altitudes over than of 1300m, combined with
steep slopes, the resulting landscape has produced a dense hydrographic network and hydraulic
dynamics. The configuration of the relief proves decisive in the trajectory and intensity of water flow.
In accordance with the fundamental laws of gravity, water follows the slopes and depressions of the
land, ultimately converging towards the river known as Tizi Ouadrene (Fig. 8).
Furthermore, the predominance of schist in the sector accentuates water infiltration, particularly in
the altered schist horizon witch its increased permeability. The position of the embankment in the lower
areas of the mountainside, combined with its orientation towards the river, aligns with the guidelines of
the hydrological scheme in the sector.

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Fig. 8. Block diagram of the site morphology. A: Condition prior to road construction. B: Condition following
road construction, with emphasis on the relative position of the landslide
Faced with this situation, and in order to minimize the adverse effects of water on the stability of the
road and its appurtenances, a road drainage system has been installed (Fig. 9). This mechanism
comprises a side ditch (Fig. 9.a and c). Its role is to canalize runoff from the roadway, shoulders and
adjacent slopes. Its function is enhanced by its connection to a culvert (Fig. 9.c), essential for redirecting
water towards the river. To counter the risk of erosion, especially where the embankment contains
backfill on the downstream side of the road, a concrete berm has been built at the junction of the shoulder

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and the top of the embankment (Fig. 9.b). It serves to channel water from the road, preventing its
dispersion and directing it towards the adjacent Wadi. However, while this drainage system ensures the
collection and evacuation of surface runoff, the issue of groundwater persists.
Fig. 9. Road drainage system. (a): the side ditch. (b): the concrete berm. (c): the culvert
6. Discussion
The roadway's construction involved substantial earth-moving activities across a span of about 40
meters in width. The process included reshaping the upstream side into a slope by excavating altered
schist to achieve a 91° incline. In contrast, the downstream side, which is the focal point of our study
due to noted instability, utilized a cut and fill approach to balance the topography. By synthesizing
topographic data, borehole logs, field observations, and geotechnical tests, we have derived a
comprehensive geotechnical profile (Fig. 10). This profile uncovers crucial embankment characteristics
and identifies the potential break line. The outlining of this rotational line is basically derived from the
indications of the detachment niche observed in situ.

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Fig. 10. Geotechnical profile of the embankment in question (conditions before sliding)
Examining this profile highlights the embankment's complex geometry, marked by a steep incline
of approximately 75% and an elevation of 11 meters. Prior research (Yazidi et al., 2017; Peridikou,
2019; Çellek, 2020), has confirmed that such geometric attributes increase the risk of landslides, by
enhancing the gravitational forces exerted. Furthermore, the particular disposition and orientation of the
underlying compacted schist stratum created a conducive pathway for the displacement of the overlaying
altered schists.
The altered schists, exhibiting a plastic consistency and significant fines content (Table 3), are
classified as category A2 according to the GMTR (2001). Such classification underscores their
sensitivity to water, a property further corroborated by mineralogical analyses (Fig. 6) revealing the
presence of highly soluble minerals like calcite and dolomite (Eppner, 2016). The detection of
manganese oxide and ankerite within these formations points to active chemical weathering processes,
a clear indicator of significant geochemical dynamics within the studied sector (Ahmat et al., 2022).
The initial manifestations of instability were directly attributable to the suboptimal performance of
backfill materials, which led to settlement and fissuring on road surfaces, facilitating water ingress to
the embankment core. These materials, sourced from local excavations, categorized under fragmentable
argillaceous rocks R34. Rocks within this group evolve, releasing fine, plastic, and water-reactive
particles, alongside a decrease in mechanical strength. This aligns with Cherifi's 2022 study on our
sector's schists. Temperature fluctuations worsen this evolutionary process, causing expansion and
contraction of the materials, that weaken their structural integrity. Excavation and road traffic also
increase stress on these materials. The GMTR (2001) stipulates several criteria for the use of such
evolving materials. These include a rigorous compaction, post-extraction fragmentation, and
stabilization with lime (particularly under conditions of increased moisture). In addition, preliminary
evaluations are required to identify appropriate extraction and compaction techniques, ascertain the
particle size distribution, and devise designs prioritizing impermeability. Adhering to these
recommendations can enhance the performance of backfilled schists.

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As previously discussed, schists as backfill or present in their natural state, are inherently sensitive
to water. Furthermore, the pronounced permeability of altered schists facilitates water flow, which
predisposes them to instability risks. This susceptibility is further exacerbated by the destabilizing
effects of hydraulic pressures and erosion (Sun, 2020). Despite the drainage system's capacity to manage
surface runoff, it falls short in preventing subsurface water infiltration, leading to pronounced
percolation. This situation was significantly worsened by the heavy rainfall event on April 6, 2022,
identified as a major trigger for the subsequent landslide. Several authors (Kim et al. 2004; Xue et al.
2008; Fort, 2011), have underscored the substantial rainfall as a critical triggering factor.
Aware of the significant impact of hydrology on slope stability, this article proposes an enhancement
of the initial drainage system to align with the hydrological, morphological and lithological
characteristics of the studied site. The initiative advocates for the strategic installation of a deep drainage
trench aimed at managing groundwater, as detailed in Fig. 11. The trench structure is equipped with an
impermeable geomembrane acting as a barrier against lateral water infiltration towards the embankment,
complemented by filling with water-resistant draining material, that guide the water to a perforated pipe,
thus directing the flow towards a suitable outlet. The addition of a geotextile is recommended to maintain
the functionality of the drainage system by preventing clogging by fines. This approach constitutes a
systematic geotechnical strategy addressing the challenges posed by adverse hydrological dynamics.
7. Conclusions
Our comprehensive analysis of geotechnical instability in road embankments, with a focus on a
landslide event along the Taza-Al Hoceima expressway in Northern Morocco, has determined that
intense rainfall serves as a primary trigger for such occurrences. Secondly, the inadequate performance
of schist backfills, combined with the embankment's complex litho-geometric structure, has been
pinpointed as a crucial determinant of this instability. Laboratory-based geotechnical and mineralogical
analyses have verified the vulnerability of schists, attributed to their reaction to water and natural
evolution. Concurrently, a notable failure in the drainage system's ability to handle subsurface water
infiltration has been observed. This shortcoming is exacerbated by the schists' permeability, alongside
the locale's hydrological and geomorphological aspects, culminating in pronounced water percolation.
Ultimately, the strategic implementation of a drainage trench offers a promising solution to these issues.

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Fig. 11. Geotechnical solutions to mitigate the impacts of negative hydrological dynamics
This study underscores the crucial role of the synergistic interplay among geotechnical, mineralogical,
hydrological, and morphological factors in the instability of embankments. It stresses the importance to
take into account the geotechnical characteristics of schists, and underscores the vital need to design
road drainage systems that are specifically tailored to the local environmental conditions. Implementing
these recommendations is anticipated to significantly improve the reliability and durability of road
infrastructures. Moreover, the development of a detailed geotechnical profile of the studied
embankment, has paved the way for new research perspectives. This entails using the limit equilibrium
method in inverse analysis to determine the shear strength parameters of altered schist. Such a method
is crucial for advancing towards the modeling and optimization of reinforcement strategies, such as the
construction of retaining walls.
Acknowledgements
We gratefully acknowledge the anonymous reviewers for their valuable critiques and suggestions,
which greatly improved the manuscript's quality. Special thanks to “LABOCONTROL”, where the first
author serves, for providing essential geotechnical resources, to “PDEW of Taza” for providing valuable
data that enriched our research, and to the engineering firm “B.E.T. GENIE CIVIL 3” for its financial
support, essential for this project's realization.
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