Landslide is one of the earth's most destructive disasters, is often triggered by major earthquakes. Among all the damages caused by earthquakes, landslides constitute a significant portion [1, 2]. There has been continuous progress in the development of methods for estimating landslide displacement during an earthquake since Newmark [3] proposed the sliding block method for predicting the cumulative permanent displacement of a slope [1, 4]. A numerical study utilizing the Newmark slope sliding model is presented in Fig. 1, which depicts the different displacement values and failure surfaces associated with both geosynthetic-reinforced and unreinforced slopes. The displacement evaluated by the Newmark slope sliding method is merely a design parameter determined by an artificially simplified slope model ignoring several important mechanisms; for example, continuous shear failure rather than a fixed slip surface, cyclic deterioration of soil materials (including pore-pressure buildup) rather than a fixed friction angle, etc. It is assumed that once soil has yielded, its resistance remains constant as displacement increases. However, this method may not accurately model the system without structural elements (such as geosynthetics) that restrain ground movement. Displacement will stretch geosynthetic reinforcements, thereby increasing their restraint capacity (it is mandatory that they are designed not to yield/rupture when subjected to full displacement). Accordingly, the primary Newmark method does not accurately represent the slope's deformation. Thus, it is essential to develop equations that are easier to understand and more effective as well. In this regard, several modifications have been suggested to the primary Newmark slope sliding model to achieve a more accurate estimation of slope displacement by modeling the dynamic slope response. Generally, these approaches can be categorized into three types:
i. “Rigid-block analysis”, discrete-element assembly is a structure made from rigid components without glue or other joining mechanisms. In the approach, compressive forces occur at the vertices of the interface to model a unilateral contact between blocks. Originally, rigid-body assumed that normal forces could occur without deformation. Once the shaking has stopped, a permanent displacement will result from accumulated unrecoverable deformations. In this theory, a sliding soil mass can be regarded as an object subject to seismic forces.
ii. Based on the rigid block analysis, Makdisi and Seed [5] presented the “Decoupled approach”. The dynamic response is calculated to measure the block's displacement based on the system's equivalent acceleration [6]. Additionally, in decoupled procedures, the dynamic response of the embankment is computed independently of the sliding mass displacement.
iii. “Coupled analysis”, in which deformation of the sliding mass is calculated concurrently with its dynamic response [7, 8]. Then, the ground motions are investigated regarding the plastic sliding displacements [8, 9].
It is widely used by researchers to assess earthquake landslide hazards using the Newmark sliding displacement method. Many assumptions are involved in the traditional Newmark slope sliding model, which results in various levels of uncertainty in displacement results. There have been several research studies based on ground-motion intensity such as critical acceleration to develop regression-based Newmark slope sliding prediction equations for slope displacements.
Ambraseys and Menu [10] proposed the first equation to predict displacement within the framework of the Newmark slope sliding models (Dn). The consequence Eq. (1) describes their work in the best possible light:
Log Dn = 0.9 + Log ((1 - ac / amax) 2.53 × (ac / amax) −1.09) ± 0.3; (1)
where the term ac represents the critical acceleration (measured in g), amax represents the maximum acceleration recorded in a strong-motion record, Dn is in centimeter units, and the last term indicates the model’s estimation error. According to Newmark analysis, sliding is caused by input accelerations exceeding critical accelerations (ac), and the block keeps sliding until zero relative velocity is achieved between the block and the ground surface [11, 12]. The critical acceleration is the acceleration that causes the factor of safety to reach 1.0:
a c = (F.S − 1) gsin α; (2)
where g is the acceleration of gravity, F.S is safety factor, and α is angle between the sliding surface and the horizontal. Jibson [12] derived the following regression Eq. (3) by analyzing 11 strong-motion records:
Log Dn = 1.46 Log Ia − 6.642 ac + 1.546 ± 0.409; (3)
where Ia is the Arias intensity (in meters per second). In light of that, the in situ measurements have shown that critical acceleration can be effectively normalized by the maximum ground acceleration (amax). Therefore, Jibson [2] developed the regression Eq. (4) with all logarithmic terms:
Log Dn = 0.561 Log Ia − 3.833 Log (ac / amax) -1.474 ± 0.616 (4)
Rathje and Saygili [13] proposed Eq. (5) by interfering combinations of Mw, Ia, and amax:
Ln Dn = 4.89–4.85 (ac / amax) − 19.64 (ac / amax)2 + 42.49 (ac / amax)3 − 29.06 (ac / amax)4 + 0.72Ln (amax) + 0.89 (Mw -6) + 0.789 (ac / amax) − 0.539 (ac / amax)2 + 0.732; (5)
In this case, the scalar model standard deviation as a second-order polynomial is represented by the last three terms. Hsieh and Lee [1] developed regression equations for both global and local purposes. They also considered both soil and rock site conditions. Eq. (6) has the goodness of fit and less estimation error:
Log Dn = 0.847 Log Ia − 10.62 ac + 6.587 ac × Log Ia + 1.84 ± 0.295 (6)
In addition, Paulsen and Kramer [14] developed a practical model for assessing post-earthquake serviceability after earthquakes by estimating the permanent displacement of reinforced slopes. As a result of their study, it was demonstrated that the model is capable of predicting critical acceleration and permanent displacement reasonably well. Mojallal et al. [15] proposed an approach for calculating the coefficient of critical acceleration and displacements in the permanent phase of GRS walls. In this way, in accordance with Newmark’s sliding block method and upper-bound theory, groups of charts have been proposed to predict the permanent displacements due to sliding. Using the horizontal slice method and limit equilibrium. Varzaghani and Ghanbari [16] proposed a novel approach to investigate displacement of slope-adjacent foundations due to seismic activity. It is determined that the critical failure surface for different failure surfaces is the surface with the maximum strain calculated dynamically. According to the comparison, the suggested model can accurately predict seismic displacements. In addition, it was demonstrated that with an increase in slope angle and decreasing distance between the slope edge and foundation, seismic displacement increased in a non-linear manner. Du et al. [11] evaluated different types of Newmark analysis using intensity measures (IMs) considering uncertainty sources. It was found, indeterminacy for the vector-IM remains stable during ground motions magnitude and site conditions. In the end, a procedure is carried out to arithmetic uncertainty sources for a completely probabilistic Newmark slope sliding model, also it was shown that unit weight would not noticeable effects on the displacement. Liu et al. [17] employed a FEM procedure to study the seismic responses of GRS walls in the presence of different near-field earthquakes. The study investigated interaction between the ground-motion parameters, reinforcement’s forces, and lateral displacement. It was concluded that the Arias intensity is associated with the maximum reinforcement tensile strength, and the displacement is also influenced by these two parameters. Song et al. [18] investigated the effect of earthquake orientations on the probabilistic seismic displacement of slopes. Anticipant correlation of orientation- independent seismic deformation are expanded for various kind of earthquake. Statistical evaluation of ground motion-induced landslide risk was carried out for assumptive slopes, and the sliding landslide risk maps and the earthquake selection method for site condition assessment of slopes were introduced by including the impact of earthquake orientation in various kind of earthquakes. Geotechnical engineering faces a number of significant challenges when it comes to slope stability analysis since it is mathematically challenging to determine the critical slip surface of earth slopes. In an unreinforced earth slope, several methods can be used to estimate the minimum factor of safety for non-circular slip surfaces; however, for a reinforced soil slope, it cannot easily be calculated due to the additional effect of reinforcement. The particle swarm optimization (PSO) method can be used to search the critical slip surface efficiently. Shinoda and Miyata [19] calculated the slope safety factors for both reinforced and unreinforced soil slopes by considering force and moment equilibrium. To begin, sensitivity analyses were conducted to investigate the effects of PSO parameters on safety factors. An appropriate PSO parameter range for calculating the safety factor in unreinforced and reinforced soil slopes was determined based on this analysis. Sharafi and Maleki [20] employed a reinforced slope to multi-dimensional seismic loading combinations in order to assess seismic performance of the reinforced sandy slopes. They implemented reduced-scale laboratory models of a shaking table alongside the 3D explicit finite difference method. They concluded that the long-term lateral sliding displacement of the slope has the greatest impact among the combination of the axial components of motion records. The findings have also demonstrated a straightforward logarithmic connection between several intensity indicators and the lateral displacement of a reinforced sandy slope. Because of the mechanism of slope movement caused by earthquakes, and the criteria for seismic performance or failure state, assessing the seismic stability of earth slopes has long been a challenge in geotechnical engineering. A study of rotational sliding mass failures on seismic slopes was performed by Ji et al. [21] in order to resolve these issues. By integrating Newmark's sliding block theory with rotational displacement computations, the authors extended Newmark's analysis of permanent displacement. In addition, they proposed a simplified relationship between a circular failure mass's rotational and horizontal motions. To calculate the reliability index, which can be viewed as a substitute for the probability of failure, uncertainties of soil properties were introduced. A substantial amount of research has been conducted in geotechnical engineering regarding evaluation of seismic stability. In order to address this issue, Ji et al. [22] developed a revised sliding block model incorporating shear strength and dynamic critical acceleration. Additionally, the probabilistic seismic slope displacement distribution was recalculated by incorporating the uncertainties associated with the ground motion. According to their findings, displacement and Arias intensity are approximately linearly correlated on a logarithmic scale. Choudhuri and Chakraborty [23] conducted an analysis of a two-layer cohesive-frictional soil system to determine its probabilistic bearing capacity based on soil spatial variability. It is considered that the cohesion and friction angle of both layers are random fields with lognormal distributions. Numerical analyses were performed using the finite difference code. In order to estimate the bearing capacity of the footing, the Monte-Carlo simulation technique was used. Additionally, the study reviewed the effects of cross-correlation between friction angle and cohesion on the probabilistic properties of bearing capacity and failure probability. Due to significantly high estimates for the standard deviation of existing prediction equations, Nayek and Gade [24] prompted to develop new data-driven prediction models based on artificial neural network technology. Predicting slope displacement is accomplished by combining parameters associated with ground-motion characteristics with the slope's critical acceleration value. A dataset containing 13,707 data points of slope displacement was used to generate several prediction models, including scalars and vectors. The models perform well according to their efficiency. Tiwari and Lam [25] analyzed the displacement of retaining walls (RW) with base restraints during an earthquake. After shaking table experiments were performed on a reduced-scale RW model, an exhaustive finite element analysis (FE) was carried out. There were also investigations into the impact of different backfills on the seismic performance of RWs. Based on the observations, cohesionless backfill may slightly affect the displacement of base restrained RWs. An analytical model has been developed for estimating earthquake-induced displacement of base restrained RW based on results from shaking table experiments and FE simulations. In practice, soils are usually unsaturated, but the traditional approach to evaluating the stability of geosynthetic-reinforced soil structures (GRSSs) is conducted under either completely dry or saturated conditions. Because of suction-induced effects, Deng and Yang [26] developed a useful analytical method for determining the reinforcement strength required for preventing slope failure of unsaturated GRSSs under steady infiltration conditions, based on the reinforcement effect of geosynthetics. According to the results, suction stress plays a more significant role in determining the required normalized reinforcement than tensile strength cut-offs. Nazari et al. [27] examined the probabilistic stability of tiered GRS walls under seismic loads, taking into account soil spatial variability and cross-correlation between input variables. The critical slip surface was identified using random limit equilibrium methods (RLEM). Based on the results, increasing the coefficient of variation from 5 to 15% increased the failure probability from zero to around 9%, raising serious concerns about the stability of the GRS walls. Additionally, it was determined that the probability of failure decreased as the negative cross-correlation between soil cohesion (c) and soil friction angle (φ) increased. Furthermore, the random finite element method (RFEM) approach produces a higher factor of safety in comparison to circular and non-circular RLEMs, with a difference of approximately 6% from Sarma's method. The proposed formula develops a shear strength reduction method and incorporates the effects of the inertial forces acting on the reinforced soil. This allows for a more accurate estimation of the sliding displacement of the reinforced soil. A novel numerical-simulation-based slope reliability analysis (NSB-SRA) method was proposed by Chen et al. [28] to decrease the time required for slope reliability assessment when considering spatial variability. In the first step of building a multivariate adaptive regression spline (MARS) model, the dual dimensionality reduction technique was employed to greatly reduce random variables. Following that, NSB-SRA was performed on samples selected by response conditioning method based on MARS models predictions. As a final step, two examples of slopes with spatially variable slopes are presented in order to validate the proposed method. According to the results, MARS in combination with FDM can perform NSB-SRA efficiently. Co-seismic landslides are often triggered by earthquake-induced soil displacement on slopes. In this regard, Ji et al [29] developed Newmark slope sliding model that takes into account both vertical and horizontal ground motions when estimating dynamic pore water pressure. Using the proposed model, the continuous variations in seismic yield acceleration at almost saturated and unrestricted soil slopes can be quantitatively described. As a result, the frequency distribution characteristics of the ground motions can be reasonably used to predict the accumulated seismic displacement. Various researchers used the modified Newmark sliding displacement method in order to identify slopes at risk for landslides resulting from a future earthquake. Using the Newmark slope sliding displacements method, Cheng et al. [30] developed a deep neural network (DNN) prediction and a hybrid prediction models using ground-motion severity indicators. Across a broad range of slope conditions, a significant number of ground motions and critical accelerations (ac) samples were used to generate the proposed model. Comparing the proposed model with conventional regression models, significant reductions in standard deviation can be achieved. To demonstrate its effectiveness in engineering applications, the proposed model were applied in probabilistic slope displacement hazard analyses. Furthermore, geosynthetic-reinforced pile-supported embankments (GPEs) are currently the most commonly used method for practical projects. Xie et al. [31] proposed pile-supported geosynthetic-reinforced soil wall (PGSW) technology for widening embankments using a centrifugal model. Additionally, the cut slope ratio of the existing embankment in PGSW was analyzed using finite difference numerical models. In the PGSW-based technology, the settlements of the existing embankment and the widened portion were smaller than in the GPE-based technology.
The current study developed a performance function for slopes with geosynthetic reinforcement layers. The approach used numerical simulations, statistical analysis, and ground-motion data, which designed 12 control parameters for the slope. Even though the present study followed the same directions as previous investigations, it has undergone an evolutionary phase. Several important differences distinguish the present study from previous research. This study provides a computation programming code using Wolfram Mathematica for calculating displacement based on double integration of acceleration time-history. Consequently, this approach is able to estimate the maximum sliding displacement of reinforced slopes for varying soil, geosynthetics, and seismic conditions. By developing a stochastic model predictive approach and integrating advanced optimization search techniques, an innovative framework for estimating probabilistic lateral sliding displacement of GRS slopes is proposed, utilizing Newmark's sliding block analysis as a basis. The complementary optimization search techniques in conjunction with non-circular methods in this study are part of a comprehensive investigation that improves the accuracy of seismic sliding displacement measurements compared with previous studies. As part of this study, a synthetic dataset containing 972 data points was also generated regarding the seismic sliding of geosynthetic-reinforced soil slopes under strong-ground motion data based on numerical analysis results. Unlike previous studies that focused mostly on unreinforced slopes, this study simulates the realistic behavior of GRS slopes taking into account several uncertainty sources such as soil spatial variabilities, reinforcement properties, and failure surfaces. It also examined combinations of seismic characteristics relating to displacement (Log Dn) as well as Housner intensity (HI), moment magnitude (Mw), closest distance to the rupture surface (Rrup), and significant duration (T5 − 75). Furthermore, this study examined the critical accelerations and cumulative permanent displacements of GRS slopes based on slope properties and seismic motion characteristics. A further originality is that the study illustrates the relationship between motion characteristics such as Arias intensity and critical acceleration ratio on a logarithmic scale. It was concluded, the slope performance is strongly influenced by this factor under operational conditions. Using Spearman correlation coefficients, the most influential motion characteristics are identified, and further insight is gained into geosynthetic-reinforced soil slope dynamics. As a result of the verification, it is confirmed that the proposed formula is well adapted to previous research results.