Pile-reinforced Slopes Research Articles

Reliability analysis and risk assessment of pile-reinforced slopes considering spatial soil variability and site investigation

ABSTRACT Site investigation data is of great significance for practical slope stability analyses and designs. Previous studies on the probabilistic analysis of pile-reinforced slopes, however, rarely considered the influence of site-specific information, which may lead to a biased judgment of the stability of the soil-pile system, thus resulting in unreasonable designs. This paper proposes a new integrated probabilistic framework to analyse the probabilistic characteristics and quantitative risk of the pile-reinforced slopes considering site investigation data. Particularly, with the aid of the framework, the responses of the stabilising piles under different schemes of investigation boreholes are systematically studied. The Random Finite Difference Method within the framework of Monte Carlo Simulation (MCS) and Subset simulation is employed to explore the uncertainty within the pile-reinforced slope and the associated pile responses. A soil slope is taken as an illustrative example to validate the effectiveness of the proposed framework through various parametric studies on the investigation scheme of boreholes (e.g., numbers, locations, and sampling intervals). It is found that the stability results obtained from the deterministic analysis with mean soil properties and the conventional unconditional random field MCS may be biased compared to the results by the proposed framework considering real-site situations.

Hybrid response surface method for system reliability analysis of pile-reinforced slopes

To consider the complex soil-structure interaction in a pile-slope system, it is necessary to analyze the performance of pile-slope systems based on a three-dimensional (3D) numerical model. Reliability analysis of a pile-slope system based on 3D numerical modeling is very challenging because it is computationally expensive and the performance function of the pile failure mode is only defined in the safe domain of soil stability. In this paper, an efficient hybrid response surface method is suggested to study the system reliability of pile-reinforced slopes, where the support vector machine and the Kriging model are used to approximate performance functions of soil failure and pile failure, respectively. The versatility of the suggested method is illustrated in detail with an example. For the example examined in this paper, it is found that the pile failure can significantly contribute to system failure, and the reinforcement ratio can effectively reduce the probability of pile failure. There exists a critical reinforcement ratio beyond which the system failure probability is not sensitive to the reinforcement ratio. The pile spacing affects both the probabilities of soil failure and pile failure of the pile-reinforced slope. There exists an optimal location and an optimal length for the stabilizing piles.

Landslide Management for Batu Tulis – Cross Bogor – Sukabumi Station Double Lane Project at STA 5+550

In the implementation of the St. Batu Tulis – Lintas Bogor – Sukabumi STA 5+550 project, a significant challenge arose with the occurrence of an avalanche during construction, attributing landslides to substantial land subsidence caused by the destabilization of the slope's soil or rocks. This disruption significantly impacted construction planning, particularly in terms of cost considerations. This study conducted a comprehensive comparative analysis of the stability of the original embankment slope and slopes reinforced with gabions (measuring 2m x 1m x 0.5m), sheet piles (type W-400 A-1000), and bored piles (size D600). To evaluate the stability, it was imperative to determine the safety factor (SF) and slope deformation under applied loads. The Plaxis 8.6 program was employed for the analysis, incorporating all relevant soil parameter data. Safety factor values were calculated as 1.67 for the gabion-bored pile combination slope, 1.62 for the sheet pile-reinforced slope, and 1.63 for the bored pile-reinforced slope. Estimated costs for slope strengthening were as follows: IDR 3,525,789,199.92 for sheet piles, IDR 2,180,309,258.00 for bored pile-gabion combination, and IDR 6,689,603,822.00 for bored piles alone. The budget for slope reinforcement with gabions proved more economical by IDR 1,345,479,941.92 compared to sheet piles and IDR 4,509,294,564.00 compared to bored piles. The reinforcement type selection was based on a cost analysis, prioritizing lower expenses while ensuring construction feasibility. Gabions offer advantages such as economical prices, flexibility, and simple construction methods, but they have drawbacks, including susceptibility of galvanized coated wire to water conditions with high salt or acid content and requiring a wide area for construction due to their large size. Sheet pile reinforcement is resistant to corrosion, durable, and has good performance, but it is unsuitable for supporting very high soil due to the requirement of a large cross-sectional area and not suitable for use in rocky soils due to piling difficulties.

High fill slope collapse: Stability evaluation based on finite element limit analyses

The stability of high fill slopes, which are typically encountered when building airports in mountainous areas, is influenced by complex geotechnical profiles, the fill strength, reinforcement, and rainfall conditions. On 3 October 2009, a catastrophic landslide occurred at Panzhihua Airport in Sichuan Province, China. Investigations indicated that this event was attributable to the presence of carbonaceous mudstone. However, the overall stability of the high fill slope in different construction phases has not been explored. In this study, finite element limit analyses were performed to examine the overall stability of a critical section of the high fill slope in 11 cases that differed in terms of their strength parameters, reinforcement, and rainfall conditions. The results indicate that the original slope stability determined using parameters based on the laboratory shear tests of fill materials was overestimated. Furthermore, the original slope reinforcement with three rows of stabilising piles was ineffective. The safety factor of the pile-reinforced slope was computed to be 0.95 when rainfall infiltration was considered, and the predicted slip surface coincided with the actual failure surface. Random field limit analyses of this slope indicated that the failure probability increased under the assumed rainfall infiltration conditions. Remediation plans could ensure stability against landslides. Overall, reliable parameters and methods must be used to calculate the stability of high fill slopes.

First order reliability-based design optimization of 3D pile-reinforced slopes with Pareto optimality

As verified structures for landslide mitigation, stabilizing piles are often adopted to treat local failure zones of width-limited soil slopes. To achieve a balance between slope safety and construction cost, an optimized piling scheme for treating width-limited soil slopes should be obtained through three-dimension (3D) stability analysis. In this regard, this paper presents a novel calculation framework for the multi-objective optimization (MOO) design of stabilizing piles. It is based on the first-order reliability method (FORM) and considers a 3D width-limited slope failure with geological uncertainties. The study first develops a deterministic 3D stability model of pile-reinforced slopes using limit analysis. Accounting for soil shear strength uncertainties, reliability analyses of 3D reinforced slopes are conducted based on the prescribed pile-reinforcement patterns. Then, a multi-objective probabilistic design procedure combining the Pareto front and reliability analysis results is proposed. The effectiveness and significance of the proposed MOO design framework are demonstrated through two illustrative examples: one involves designing stabilizing piles in a homogenous slope, and the other involves designing for an inhomogeneous earth slope with depth-dependent soil cohesion. To gain better understanding of the probabilistic impact of uncertain pile design parameters on reinforced slope stability, comprehensive parametric studies are conducted.

Reliability analysis of pile stabilized earth slopes using weighted uniform simulation method

The finite element method (FEM) is now widely used for stability analysis of earth slopes reinforced with stabilizing piles for the advantages of better simulation of soil–pile interactive behaviors and clearly capturing the complex failure mechanism of pile-reinforced slopes. However, the implementation of probabilistic simulation to model the influence of inherent random variables onto reinforced earth slopes is still challenging due to the extensive computational resources required for the repeated execution of the Finite Element Method (FEM) simulations. This paper proposes a framework for probabilistically analyzing the pile-reinforced earth slope based on a weighted uniform simulation (WUS) method implemented by secondary development of ABAQUS-via-Python codes. Using the proposed method, important information of probabilistic indices can be obtained with less computational cost, and the influence of different pile design parameters on the probabilistic FEM stability analysis of reinforced slopes is systematically studied. The reliability indices β and the most probable failure points (MPPs) for optimal designs of pile-reinforced earth slopes under different pile design parameter combinations (L, Lx/Ls, S, D) are obtained, which can provide useful reference information for conducting slope reinforcement practicing works. In addition, the influence of uncertainty and correlation of soil strength parameters on the reliability of the reinforced slope is also investigated.

Reliability analysis of pile-reinforced slopes in width-limited failure mode considering three-dimensional spatial variation of soil strength

Stabilization pile is a common measurement for landslide mitigation. In previous literatures, the deterministic safety factor Fs method has been well established for pile-reinforced slope stability analysis, for example by limit analysis. However, the Fs method by itself cannot reflect the inherent uncertainty and spatial variability of mechanical properties of soil. This paper presents a probabilistic analysis procedure for width-constrained pile-reinforced slope where the failure pattern and soil spatial variability are both accounted for under three-dimensional (3D) condition. A modified discretization kinematic analysis-based mechanism is employed as the deterministic model. The spatial variability of cohesion c and friction angle φ is modeled as lognormal random fields by using the Karhunen–Loève expansion. The sparse polynomial chaos expansion (SPCE) is used to construct the meta-model to reduce the computational cost in high dimensional stochastic problems. The failure probability, probability density function (PDF), and other useful reliability results can be provided by performing Monte Carlo simulations of the proposed SPCE meta-model. Finally, the influences of soil spatial variability, slope geometry, and pile parameters on the slope reliability are analyzed. The combination of the modified discretization mechanism and SPCE provides a useful tool for the probabilistic analysis of pile-reinforced earth slopes under 3D condition. The probabilistic simulation results are also helpful for reliability design of pile-reinforced slope in practice.

Inclination Factors for Bearing Capacity of Strip Footings on Sheet Pile Reinforced Slopes

Inclination Factors for Bearing Capacity of Strip Footings on Sheet Pile Reinforced Slopes

Hybrid Response Surface Method for System Reliability Analysis of Pile-Reinforced Slopes

Hybrid Response Surface Method for System Reliability Analysis of Pile-Reinforced Slopes

Probabilistic analysis of pile-reinforced slopes in spatially variable soils with rotated anisotropy

Stabilizing piles have been widely used to remediate landslides and reinforce potentially unstable slopes. Previous investigations on the stability analyses of pile-reinforced slopes, however, were mainly based on deterministic analysis methods, where the spatial variability of soil properties was rarely incorporated. Meanwhile, the assumption of isotropy and horizontal transverse anisotropy in previous studies may bring bias to the slope reliability assessment, and thus the optimization design of piles. This study hence aims at systematically investigating the influence of soil spatially variable anisotropy on statistical characteristics of the factor of safety, failure mechanisms, and probability of failure (Pf) of pile-reinforced slopes. An integrated probabilistic analysis framework is used to obtain an optimal reinforcement scheme of stabilizing piles considering different rotational angles of soil strata. Subset simulation is used to enhance the computational efficiency for reliability analysis. A hypothetical slope and a practical slope are studied as illustrative examples with various parametric studies. Results show that the rotated anisotropy has a significant influence on the performance of pile-reinforced slopes and can largely affect the Pf depending on the strata inclination. For slopes with different rotational angles of strata, the number of critical slip surfaces and the slip band range are different and thereby result in different optimal pile designs.

STABILITY CALCULATION OF PILE-REINFORCED SLOPES BY THE LIMIT EQUILIBRIUM METHOD CONSIDERING SLIDING RESISTANCE OF PILES ACCORDING TO ITO-MATSUI METHOD

In the study, advantages and disadvantages of the calculation methods for overall sliding stability of pile-reinforced slopes considering sliding resistance of pile were summarized and analyzed. An automatic program for stability calculation of pile-reinforced slope was established based on the limit equilibrium method considering sliding resistance of piles according to Ito-Matsui method. The program was used to evaluate the effects of the piles, such as position and spacing of the piles on the stability of the slopes.

Vulnerability analysis of pile-reinforced slope under the condition of near-fault impulse ground motions

In order to analyze the impact of the near-fault pulse ground motions on the slope, the method of seismic vulnerability analysis based on IDA is introduced into the stability evaluation. Taking the slope reinforced by stabilizing piles as an example, a typical analysis model is established. The seismic performance is divided into four stages: basically intact, partial damage, severe damage and overall instability. A large number of calculations are used to compare the instability probability of slopes with near-fault and far-field ground motions. The results show that: 1) The calculation model which combines the Newmark and the limit analysis method can reflect the difference between the near-fault and the far-field ground motions. 2) The IM-DM curve with indexs of PGA and displacement has a better fitting effect. The vulnerability analysis based on IDA can be used to evaluate the slope failure risk under seismic loads. 3) The IDA curve shows a monotonous increasing trend. When the seismic intensity is lower(GPA=0∼0.5), there is no obvious difference between the vulnerability curves of the near-fault and far-field. As the intensity increases(GPA=0.5∼1.2), the failure probability of near-fault is significantly higher than the far-field. Meanwhile, the failure mode changed from the partial failure to the complete failure. It is clear that near-fault ground motions have the characteristics of large energy and strong impact, which are more likely to cause slope instability. If the impact of the near-field earthquake is ignored, the disaster may be underestimated.

Pile reinforcement behavior and mechanism in a soil slope under drawdown conditions

Piles are an effective measure for landslide protection under various loading conditions. However, the pile reinforcement mechanism of slopes has not been systematically investigated in previous studies under drawdown conditions. A series of centrifuge model tests were conducted on slopes with various pile reinforcement layouts under drawdown conditions to study the progressive slope failure process and slope failure mechanism. Compared with the unreinforced slope, the pile-reinforced slope had a greater safety limit and underwent less deformation. The failures of the unreinforced slope and pile-reinforced slope were both progressive from the top to the bottom of the slope under drawdown conditions with the same mechanism and could be described in terms of the significant coupling between the deformation localization and local failure. The pile reinforcement mechanism was clarified because the piles delayed the occurrence of deformation localization and decreased the localization degree of the slope under drawdown conditions. The reinforcement effect of piles includes two aspects: the compression enhancing effect and shear reducing effect. The compression enhancing effect was dominant near the piles and gradually decreased with increasing distance from the piles, and the shear reducing effect was dominant near the potential slip surface.

Mass-gravity-scaling technique to enhance computational efficiency of explicit numerical methods for quasi-static problems

Large deformation numerical analysis adopting explicit integration scheme is commonly employed in geotechnical analysis to simulate quasi-static problems involving large soil deformations. The computational time for the conduct of such analysis is often very time consuming particularly for complex 3-dimensional soil-structure interaction problems. As an extension to the mass-scaling technique, a mass-gravity-scaling (MGS) technique is proposed in this study to improve the computational efficiency substantially. By scaling the material density and model gravity correspondingly, the soil initial stress state that is essential for realistic soil response can be maintained. This enables the increase in the critical time step resulting in a significant reduction in computational time. Three quasi-static large soil deformation geotechnical problems involving T-bar penetration, spudcan-pile interaction, and pile-reinforced slope are presented to illustrate the application of the MGS technique simulated in finite element (Coupled Eulerian-Lagrangian and Updated Lagrangian) and finite difference methods. It is established that an appropriate scaling factor should be chosen by considering a trade-off between computational time and accuracy of analysis. For selected problems, a hybrid-MGS technique can be employed by selectively applying different scaling factors over specific domains to improve the accuracy and efficiency of the solution technique.

Centrifuge model tests on pile-reinforced slopes subjected to drawdown

Piles are generally an effective way to reduce the risk of slope failure. However, previous approaches for slope stability analysis did not consider the effect of the piles coupled with the decrease of the water level (drawdown). In this study, a series of centrifuge model tests was performed to understand the deformation and failure characteristics of slopes reinforced with various pile layouts. In the centrifuge model tests, the pile-reinforced slopes exhibited two typical failure modes under drawdown conditions: across-pile failure and through-pile failure. In the through-pile slope failure, a discontinuous slip surface was observed, implying that the assumption of the slip surface in previous stability analysis methods was unreasonable. The test results showed that drawdown led to instability of the piles in cohesive soil, as the saturated cohesive soil failed to provide sufficient constraint for piles. The slope exhibited progressive failure, from top to bottom, during drawdown. The deformation of the piles was reduced by increasing the embedment depth and row number of piles. In addition, the deformation of soils outside the piles was influenced by the piles and showed a similar distribution shape as the piles, and the similarity degree weakened as the distance from the piles increased. This study also found that the failure mechanism of unreinforced and pile-reinforced slopes induced by drawdown could be described by coupling between the deformation localization and local failure, and it revealed that pile-reinforced slopes could reduce slope deformation localization during drawdown.

Statistical Assessment of Factor of Safety for Pile-Reinforced Slopes

AbstractStatistical design of experiments was combined with coupled and uncoupled pile-reinforced slope stability analyses to draw conclusions about the factor of safety (FS) sensitivity to pile-re...

Reliability Assessment on Stability of Slopes Reinforced with Anti-sliding Piles in Spatially Variable Soils

A reliability-based analysis method considering spatial variability of soil properties was proposed for stability analysis of pile-reinforced slope system in this paper. A total of 71 three dimensional (3D) finite element simulation results were used to develop a Polynomial Regression (PR) model relating the safety factor (FOS) of the slope system to the key input parameters. The PR model was proved to be reasonably accurate with a high coefficient of determination. It was subsequently implemented into a modified spreadsheet involving First-order reliability method (FORM) and spatial variability factors to perform spatial variability and reliability analyses. Based on the results, some useful conclusions are arrived with regard to the effects of spatial variability factors. In addition, a useful guideline for geotechnical engineers to choose suitable pile locations in engineering practices is provided.

Simplified evaluation on the stability level of pile-reinforced slopes

The stability method was investigated to evaluate the stability of slopes reinforced with stabilizing piles that have become widely used as a reinforcement measure for a diverse range of slopes. A series of centrifuge model tests was conducted to investigate the three-dimensional failure behavior of pile-reinforced slopes, and four primary failure modes were summarized accordingly. A simplified slice method was proposed to analyze the stability levels of pile-reinforced slopes on the basis of an equivalent model that was devised to capture the three-dimensional pile effects. The proposed method was confirmed to be effective in evaluating the stability levels of pile-reinforced slopes with different failure modes by comparing its predicted results with the observations from centrifuge model tests. The method was easily added to the programs of previous limit equilibrium methods without requiring any additional parameters. The method was applied to the real-world pile reinforcement design for a dyke slope. The analysis results showed that the pile layout significantly influenced the safety factor and the critical slip surface of the reinforced slope. There was a pile arrangement zone for the slope in which the piles had a small contribution to the increase of the safety factor, and the zone provided an important reference for the pile reinforcement design.

Pile reinforcement mechanism of soil slopes

Stabilizing piles are widely used as an effective and economic reinforcement approach for slopes. Reasonable designs of pile reinforcement depend on the understanding of reinforcement mechanism of slopes. A series of centrifuge model tests were conducted on the pile-reinforced slopes and corresponding unreinforced slopes under self-weight and vertical loading conditions. The deformation of the slope was measured using image-based analysis and employed to investigate the pile reinforcement mechanism. The test results showed that the piles significantly reduced the deformation and changed the deformation distribution of the slope, and prevented the failure occurred in the unreinforced slope. The pile influence zone was determined according to the inflection points on the distribution curves of horizontal displacement, which comprehensively described the features of the pile–slope interaction and the characteristics of reinforced slopes. The concepts of anti-shear effect and compression effect were proposed to quantitatively describe the restriction features of the piles on the deformation of the slope, namely the reduction in the shear deformation and the increase in the compression deformation, respectively. The pile reinforcement effect mainly occurred in the pile influence zone and decreased with increasing distance from the piles. There was a dominated compression effect in the vicinities of the piles. The compression effect developed upwards in the slope with a transmission to the anti-shear effect. The anti-shear effect became significantly dominated near the slip surface and prevented the failure that occurred in the unreinforced slope.

An analytical method for a slope reinforced with rigid piles

Stability analyses for a slope are mainly performed using limit equilibrium procedures that calculate a safety factor against shear failure. However, for slopes reinforced with rigid piles, failure modes other than shearing can be critical (i.e. the bending failure). Assuming that the rigid piles in a slope fail due to bending, this paper proposes an analytical method incorporating soil arching for the stability analysis of a rigid pile-reinforced slope. To validate the analytical model and perform the stability analysis of a pile-reinforced slope, a three-dimensional numerical simulation technique using the shear strength reduction method is carried out. It shows that the safety factors predicted by the numerical simulation agree well with those of the analytical method, with the differences being less than 16·0%. The safety factor is found to increase with increase in the bending strength of rigid piles; it also increases as the effective cohesion and effective friction angle of foundation soft soils increase. It is also shown that the effective friction angle of soft soils is the most influential factor affecting the safety of a rigid pile-reinforced slope.