Nail Inclination Research Articles

Influence of load parameters during landslide slope reinforcement with soil nails based on self-drilling hollow steel bars on their bearing capacity and strength properties

Introduction. Soil nails are widely used to reinforce landslide slopes and ground-retaining structures in many countries, including Russia. The interaction of soil nails with the soil base is of high interest to both engineers and researchers. The method of increasing the stability of landslide slopes with soil nails has proved to be versatile and cost-effective. However, the process of designing soil nails is usually carried out using empirical and semi-empirical methods that may ignore a number of important factors.Aim. To determine the most optimal angle of soil nail inclination, as well as to analyze the characteristics of soil movement of a landslide slope along a potential sliding surface and their influence on the bearing capacity of the soil nail and its strength characteristics.Materials and methods. A review of scientific publications on the influence of load parameters during landslide slope reinforcement with soil nails based on self-drilling hollow steel bar on their bearing capacity and strength properties was carried out. The review sample included 11 publications most relevant to the topic under study. Calculations were carried out using the PLAXIS 2D software environment.Results. The conducted calculations and literature review allowed the optimal angle of soil nail inclination in the slope to be established, which corresponds to a value ranging from 0° to 5° to the horizon. The study also showed that the development of shear stresses along the soil nail in time exhibits a non-uniform nature. Therefore, the assumption of a constant value of shear stresses along the entire length of the nail or anchor root can lead to an overestimation of the soil bearing capacity.Conclusions. The obtained results have confirmed the relevance of further research into the influence of load parameters during the reinforcement of landslide slopes using soil nails.

Numerical investigation on performance of nail stabilised vertical cuts

Soil nailing is an earth retention technique commonly used for stabilising steep slopes, retaining excavations and helps in maintaining the ground surface at two different elevations. Ease of installation, economic efficiency and effective performance of soil nailed structures under different loading conditions has resulted in the rapid use of the technique in different temporary and permanent construction applications. This study deals with the finite element analysis of 6 m and 10 m high vertical soil nailed walls to evaluate the performance under static loading. The characteristics of structures are evaluated under different nail inclinations, nail lengths and different site conditions. The response of soil nailed structures under different parameters are assessed with respect to maximum horizontal displacement of the wall, maximum axial force developed along the nail length and lateral earth pressure distribution on the nailed wall. An optimum nail inclination of 15° and nail length ratio of 0.7 has been identified as best suited for a stable vertical cut.

Seismic evaluation of helical soil-nailed walls using shaking table testing

The effects of the nail arrangement and nail inclination on the dynamic performance of helical soil-nailed walls (HSNWs) were evaluated using a series of shaking table tests. The results showed that although a uniform increase in the nail length along the wall height significantly improved the seismic performance of the HSNWs, this improvement could also be achieved to some extent by increasing the length of the nails locally in the lower and upper halves of walls reinforced with horizontal and inclined nails, respectively. The use of inclined nails instead of horizontal ones was an efficient solution for reducing the lateral displacement, the acceleration amplification and increasing the fundamental frequency of HSNWs. The effectiveness of this solution was reduced with the use of shorter nails in the upper half of a wall and eventually minimized by reducing the length of the nails across the wall height. The nails located in the lower half of the wall were identified as having the greatest effect on the seismic performance of HSNWs when horizontal nails were used. The opposite occurred when inclined nails were used. A parabolic failure surface with a specific inflection point was observed to be the potential failure surface of the HSNW. The dimensions of the potential failure surface increased with an increase in the length and inclination of nails. Also, a combination of overturning and base sliding was identified as the predominant deformation mode in HSNWs, although the base sliding mode faded with an increase in the nail inclination.

Parametric Assessment of Soil Nailing on the Stability of Slopes Using Numerical Approach

This study focuses on the stability analysis of slopes reinforced by soil nailing. The effects of slope geometry and nail parameters on slope stability are investigated using PLAXIS 2D. Four different slope angles and three different backslope angles are considered for assessing the effect of slope geometry on the stability of a nailed slope. The factor of safety (FS) was found to decrease with the increasing values of the slope angle as well as the backslope angle. The influence of different nail parameters (nail inclination, nail length, and nail spacing) was also investigated. With the increase in nail inclination, FS was found to increase initially and thereafter, reaching a peak value followed by a drop in FS. The optimum nail inclination was found between 0 and 25° at a horizontal angle, depending on the different slope geometries, which is evident from observation of the slip surface as well. With the increase of nail length, FS increases; however, the increase was small after L/H (length of nail/height of slope) reached a value of 0.9. Moreover, increasing the length of the nail was found to be effective in reducing the lateral movement of the slope. The maximum nail forces are observed in the bottom-most row of nails and increase with the depth. The inclusion of soil nailing with optimum nail parameters can increase FS by 29–75% depending on the slope geometry, signifying the effectiveness of nailing.

Numerical Simulation of Ground Anchor-Soil Nail Retaining Systems for Academic-Learning Purposes

The ever-expanding urban architecture in developing areas requires more land space for construction purposes to be available. For this, utilizing the sub-surface areas through excavations in populous cities is now on the increasing trend. Two major concerns in such excavation projects are excavation-wall stability and the induced ground settlements which can be countered by a soil nailing-ground anchor system. In this regard, influential factors such as nail length and nail inclination angles can affect the overall performance of stabilized ground. Therefore, the focus of the present study is on how the aforementioned influence excavation-induced ground deformations. The numerical simulation is conducted using the software Plaxis 2D. The established numerical models help to explain how changes in the nails’ inclination angles and anchor lengths can change the observed behavior of the walls; from which helpful tips for practicing engineers are drawn accordingly. Such results could also be utilized for classroom presentations to aid students’ understanding of geotechnical engineering concepts.

Performance of Soil Nailing for Slope Stabilization-A Review

A landslide is a geological event involving a wide range of ground motions that leads to the collapse of soil slope. The stabilization of these soil slopes is done by constructing retaining walls to withstand lateral soil pressure. These retaining walls are costly as well as it is difficult to construct as they require wide excavation for the base or bottom slab. One of the many new solutions to slope stabilization is the soil nailing built by strengthening the steep slope by driving reinforcement into the soil. In this study, a review of the origin and mechanism of soil nailing, the construction process of soil nailed retaining walls were discussed. The failure pattern of soil nails is an important factor to be noticed which influence the stability of soil slope was discussed. Numerical studies were given, which are used to determine the adverse effect of orientation and inclination of nails on the stability of soil nailed walls. A couple of case studies were discussed to evaluate the significance of soil nailing on the stability of the slope and to retain the vertical cut. A Laboratory study was considered to estimate the effect of nail inclination and different nail arrangements on settlement of soil slope. A sequential literature review investigates the application, advantages and disadvantages of soil nailing. This study shall help in understanding the various applications of soil nailing in the civil engineering sector.

Stability analysis of mine overburden dump and improvement by soil nailing

The conventional method for carrying out stability analysis of dump involving Limit Equilibrium Method (LEM), when compared with the strength reduction method (SRM) using Finite Element Method (FEM) approach, resulted in overprediction of the factor of safety (FoS). In the present study, slope stability analysis of external overburden dump in Sonepur Bazari opencast mine has been carried out. Morgenstern Price method using constant inter-slice force function conducts the analysis of LEM using Geo-studio Slope/w, and the FEM analysis is carried out using the PLAXIS 2D 2016. The study is carried out to assess the effect of the dump’s friction angle, slope angle, height, and bench configuration. Further, the analysis considering the soil nailing is also conducted by optimizing the number of nails, the distance between nails, length of the nails, nail inclination angle. The stability analysis found that the dump is in a critical state (FoS = 0.92) with a circular failure surface. The optimum slope angle is found to be 30˚. It is observed that LEM cannot detect the increased localized stress concentration at the bench edge. Reinforcement of the dump using the soil nailing technique has affected the dump stability substantially, with an increase of 11% in the FoS; however, the effect of nail orientation on dump stability was less pronounced. Further bench provision to the dump slope increases the FoS by 27%, 21% and 19%, considering the total height of 60 m, 80 m and 100 m, respectively.

Numerical evaluation on steep soil-nailed slope using finite element method

In conventional design of soil-nailed slope, the nail parameters such as nail spacing (1–2 m), and nail inclination (10º–20º) have been recommended without considering any specific slope angle. Henceforth, this paper presents a numerical evaluation on the soil-nailed slope with flexible facing based on the finite element method in order to investigate the range of those two parameters with any size of nail head in various slope angles (45º, 55º, 65º, and 75º). Based on a minimum factor of safety (FSmin = 1.5), the analysis results indicated that the suggested range of those parameters in the conventional specification was applicable in the slope angle of 45º and 55º with any sizes of nail head. Nevertheless, it was not practical for slope angle of 65º and 75º, which required the size of nail head at least 400 × 400 × 250 mm, with nail spacing less than or equal to 1.5 m, and nail inclination from 5º to 10º.

Shaking Table Tests to Evaluate the Seismic Performance of Soil Nailing Stabilized Embankments

A series of shaking table tests will be carried out on 0.4 m high instrumented soil nailed embankments. The important parameters considered in this study consist of a combination of three different slope angles (β = 30°, 45°, and 60°), three different nail inclinations (i = 0°, 15°, and 30°), and three nail lengths (l = 0.2, 0.3, and 0.4 m). This study revealed that the effect of slope angle on the seismic resistance of steep nailed soil slopes was significant and the minimal magnitude of the facing displacement was obtained with nail inclinations of 0° and 15° for the nailed slopes without facing and with facing, respectively. A model nailed slope with a nail inclination of 15° provided better reinforcement action than the horizontally and 30° inclined nails when stabilizing soil slopes. The maximum axial nail force was obtained at approximately two-thirds of the nail length in the model slopes with facing and at the slope facing for model slopes without facing.

Pseudostatic analysis of soil nailed vertical wall for composite failure

ABSTRACT In the present study, pseudostatic method is used to analyse the stability of soil-nailed vertical wall under seismic conditions. This approach includes an additional inertial force equivalent to the dynamic load caused by earthquake. The soil surface which undergoes failure due to the static and dynamic condition is assumed to be a realistic composite failure surface rather than the conventional planar, circular or log-spiral surfaces. This study investigates the effect of various parameters such as vertical and horizontal seismic acceleration coefficients, friction angle of soil, shear wave velocity, primary wave velocity, amplification factor, nail length, spacing of the nails, and nail inclination on the stability of the vertical soil-nailed wall. A comparison study is made between the results obtained from the present analysis and the values reported in the literature. It is observed the present study with composite failure surface gives higher values of Factor of Safety compared to planar failure surface. Composite failure surface is more realistic and hence more accurate compared to a planar failure surface which gives a conservative value of Factor of Safety.

Analysis of helical soil-nailed walls under static and seismic conditions

The present study investigates the behaviour of helical soil-nailed wall in a dry cohesionless medium under static and seismic conditions. Initially, results from laboratory pullout tests are used to develop a pullout capacity equation, which is subsequently used for stability analysis of helical soil-nailed wall. A detailed parametric study is conducted to evaluate the effect of angle of internal friction of soil, nail inclination, vertical spacing of nails, number of nails, helix size, number of helices, and the face angle on the stability of the soil-nailed wall. Results from the present method are compared and validated with similar existing methods available in the literature. The results suggest that for the given input parameters, the factor of safety (FoS) values from the present method are lower than the pseudo-static and pseudo-dynamic values. Further, the study clearly highlights the significance of input excitation frequency on the FoS of helical soil-nailed walls. In addition, the effects of strain-dependent dynamic properties (shear modulus and damping ratio) on the stability of helical soil-nailed walls are studied using the newly proposed equivalent linear analysis approach. The results computed from the proposed linear and equivalent linear analysis are also compared and discussed in detail.

Numerical Analysis of Soil Slope Stabilization by Soil Nailing Technique

Slope instability may be a result of change in stress conditions, rise in groundwater table and rainfall. Similarly, many slopes that have been stable for several years can abruptly fail due to changes in geometry, weak soil shear strength or as the effect of an external force. Debris flows (i.e. slope failures) take place without any warning and can have devastating results. So, it is vital to understand the slope failure mechanism and adopt safety prevention measures. Soil nailing is one of the widely used stabilization techniques for soil slopes. In this study, soil nail technique is proposed to upgrade the existing slope in clay. A parametric study was conducted to understand the effects of different nail diameter (i.e. 25mm and 40mm) and nail inclination (i.e. 200, 250, 300, 350 and 400) on slope stability. Morgenstern-Price (i.e. limit equilibrium) method was used to determine the factor of safety of the slope. It was found that the factor of safety of the existing slope improved significantly with three rows of 40mm diameter nail at an inclination of 400.

Slope stability analysis under different soil nailing parameters using the SLOPE/W software

Slope failure is one of the major geological phenomenon that happen due to the topography and weather conditions which cause a wide range of ground movements which needed engineers to plan in order to avoid its risk on human lives and properties by an appropriate stabilizing method. Soil nailing system is considered as one of the major preventive methods and economic systems to overcome the slope failures. In this paper, soil nailing system was studied in term of inclination to determine the most appropriate values for effective stabilization of soil slope using the SLOPE/W software. To validate the results, different soil nail inclinations were applied to a case study, and the Factor of Safety (FOS) of the case study was evaluated as well. The case study is located at Genting Highlands, Pahang. Results showed that the soil nails inclination has significant effect on the stability of the soil slope. For soil slope with steepness of 30°, 45° and 60°, the best FOS found with soil nail inclination (to the horizontal) of 60°, 50° and 40° respectively. The effect of soil nails inclination gives small difference in FOS when the degree of inclination of the soil nails varies within 5° - 20° to the horizontal.

The Effect of Nail Inclination Angle on Improving the Performance of Nailing System in Vertical Excavation

The Effect of Nail Inclination Angle on Improving the Performance of Nailing System in Vertical Excavation

A Typical Design of Soil Nailing System for Stabilizing a Soil Slope: Case Study

Slope failures, is a common issue in construction industry, such that engineers have to avoid its risk on human lives and properties by an appropriate technical design of stabilizing methods. Soil nail is one of such stabilization methods. In this paper, soil-nailing system was studied in terms of inclination, spacing and length to determine the most appropriate values for effective stabilization of soil slope. To find the optimum soil nail system, different soil nail inclination, length and spacing were applied to a hypothetical homogenous soil slope (with inclination of 30o, 40o, 45o, 60o, 70o and 90o) and the Factor of Safety (FOS) was evaluated in each case. To validate the results, the optimum soil nail angle corresponding to a slope of 50o was applied to a case study slope, and the FOS of the case study slope was evaluated as well. The case study slope is located at Cadangan Menjalankan Kerja-Kerja Forensik Di Persiaran Endah, Seputeh Wilayah Persekutuan Kuala Lumpur. Results showed that the soil nails inclination; spacing and length have significant effect on the stability of the soil slope. For soil slope with steepness of 30o, 45o, 60o, 70o, and 90o; the best FOS was found with soil nail inclination (to the horizontal) of 50o, 40o, 20o, 15o, and 10o respectively. The effect of soil nails inclination on the stability of the soil-nailed walls is slight when the degree of inclination of the soil nails varies within 5o–20o to the horizontal. The stability of the slope decreases with the increase of spacing between soil nails. Soil nail length has significant effect on the stability of soil slope with deep-seated slip surface and less effect with shallow slip surface. The bond length behind the slip surface should be enough to allow the nail to use its allowable load.

Seismic analysis of nailed vertical excavation using pseudo-dynamic approach

An attempt has been made to study the behavior of nailed vertical excavations in medium dense to dense cohesionless soil under seismic conditions using a pseudo-dynamic approach. The effect of several parameters such as angle of internal friction of soil (ϕ), horizontal (kh) and vertical (kv) earthquake acceleration coefficients, amplification factor (fa), length of nails (L), angle of nail inclination (α) and vertical spacing of nails (Sv) on the stability of nailed vertical excavations has been explored. The limit equilibrium method along with a planar failure surface is used to derive the formulation involved with the pseudo-dynamic approach, considering axial pullout of the installed nails. A comparison of the pseudo-static and pseudo-dynamic approaches has been established in order to explore the effectiveness of the pseudo-dynamic approach over pseudo-static analysis, since most of the seismic stability studies on nailed vertical excavations are based on the latter. The results are expressed in terms of the global factor of safety (FOS). Seismic stability, i.e., the FOS of nailed vertical excavations is found to decrease with increase in the horizontal and vertical earthquake forces. The present values of FOS are compared with those available in the literature.

Seismic analysis of soil nail performance in deep excavation

Deep excavation is a common part of development to utilize underground space in densely populated areas. Protection of contiguous building and properties is a primary design concern space. Soil nailing is one such technique to exchange conventional retaining system for deep excavation. It will also donate to significant saving in cost and time of construction compared to conventional retaining systems. In this study an attempt has been made to have a deep vertical excavation on ground of 10 m height using soil nail wall. Also studied the enactment of soil nail wall under different nail inclination to horizontal i.e., Ѳ = 0° and Ѳ = 15° with water table. The finite element analysis of soil nail wall was carried to study the behavior of maximum horizontal wall displacement, maximum horizontal nail displacement, base heave, maximum axial force in nail, maximum shear force in nail, maximum bending moment in nail under both static and seismic conditions using PLAXIS 2D. The process of construction is carried out in stages and a value of Global factor of safety (FSG) is maintained above 1.5 to make sure its stability. The length of nail has a major impact on the behavior of soil nail wall system; increase in nail length will increase the FSG. Results of the numerical analysis direct that the use of soil nail wall is desirable to impart stability to retaining systems.

Numerical Analysis of the Effects of Soil Nail on Slope Stability

Soil nailing is one of the good techniques for the improvement of natural and artificial slope. By the application of soil nails the stability can be increased of an unstable slope. The appropriate position of reinforcement can give the ultimate result, and it will be solution of reducing cost. In this paper, an attempt has been made to show the stability of a reinforced dry slope at different nail angles with horizontal axis, and determine the optimum nail inclination to get maximum factor of safety. The analysis was based on numerical analysis by using SLOPE/W (Geo-slope 2007). The factor of safety has been determined using the limit equilibrium (LE) method within the Morganstern-Price method along with MohrCoulomb expression. The results show that the factor of safety (FOS) of slope increases with the application of soil nail. The results also show that with the increase of inclination the factor of safety of the slope increases, but after reaching the maximum value further increases of inclination it decreases. The optimum angle of nail was found at 30 with the horizontal.

Analysis of resistance factors for LFRD of soil nail walls against external stability failures

This paper presents reliability analyses of soil nail walls against two external ultimate limit states, global and sliding stabilities, which are related to the external stability failures of soil nail walls. Reliability analyses are conducted using Monte Carlo simulation technique. Soil nailing is a popular retaining system in highway construction and slope stabilization, and its current design practice is still based on the working stress design. There remains a need to establish a more rational design framework—load and resistance factor design—based on the concept of limit state design and reliability analysis for soil nail walls. The development of load and resistance factor design approach must consider multiple ultimate limit states, associated with external, internal, and facing failures. The analyses of resistance factors against two external failures are conducted in this study considering various influencing factors, including statistical parameters of soil friction angle, ultimate bond strength between soil and nails, soil type, wall geometry (wall height, back slope angle, and face batter angle), and nail configurations (nail inclination angle, drillhole diameter, and nail spacing). In the end, a series of resistance factors are proposed for potential application of load and resistance factor design approach against external failures for soil nail walls according to different design codes.

Stability Analysis of Slope under Different Soil Nailing Parameters Based on the GeoStudio

In order to investigate the influence of different soil nailing parameters on the safety factor of a slope, the slope stability is analyzed by the GeoStudio software with different analysis methods. Soil nailing parameters (such as nail inclination, nail horizontal space, nail diameter and length) that influence the slope stability are analyzed by the Morgenstern-Price method. As the results show, the slope has the highest safety factor when the obliquity of soil nailing is about 15°, the safety factor decreases with the increase of soil-nail horizontal space with an evident acceptable space range of 2 m or less and increases linearly with the increase of soil-nail diameter and length. However when the soil-nail length equals approximately the height of the slope, the safety factor increases slowly. These results can provide a design base for field engineers.