Soil Nailing System Research Articles

Safety assessment of excavation with fault tree analysis

How to reduce the probability of failure during the excavation has caused an increasing concern in recent years in China. Fault tree analysis (FTA) is a systematic method of analysing events that lead to an undesirable event and it may be a feasible way to analyse this probability. First, statistical analyses on 342 actual excavation accidents in China are performed based on different accident causes, types of excavation supporting systems and excavation depths. Their frequency distributions are obtained to better understand the problem. Then, the FTA theory is introduced and the fault trees of the soil nailing system and cement–soil retaining wall for safety assessment are established. A case study of safety assessment of soil nailing system for excavation with FTA is carried out and the result shows FTA is useful for safety assessment of excavation.

New Soil Nail Material—Pilot Study of Grouted GFRP Pipe Nails in Korea and Hong Kong

The current method of steel bar soil nail construction is both labor intensive as well as expensive and many engineers are considering the use of new soil nail materials. In the present pilot test, an innovative soil nail is constructed by light weight high strength glass fiber-reinforced plastic (GFRP) pipe with the Tube a' Manchette grouting technique. It is found that this new soil nail system can be handled easily on sites with difficult access. Extensive laboratory as well as field tests were carried out on the GFRP pipe nails and the grouted soil mass and numerical modeling of a field test was performed. The installation of the GFRP pipe, laboratory, and field test results that were carried out in Hong Kong and Korea are discussed in this paper.

INFLUENCE OF NAILS LENGTH ON THE BEHAVIOR OF NAILED-SANDY SOIL SLOPE

Soil nailing is a mean of stabilizing earth slope by installing in situ closely spaced steel or plastic bars called nails in the ground. The installation is usually in progressive manner from top or bottom as excavation proceeds. There are many factors that affected the behavior of soil nailing system such as: horizontal and vertical spacing between nails, soil density, length, and method of installation. This research concerns on nail′s length, which is one of the most important factors. In this work, three dimensional laboratory model, 1760 mm x 850 mm x 1000 mm, was set up simulate nailed sandy soil slope of height 7.00 meter with model scale ‘’10’’. The experimental program was designed and constructed to investigate the behavior of nailed soil slope system with 5.00 mm in diameter steel bars during, after construction, and under footing pressures at different nails length. The results indicate that increasing nails length up to a length equals to the height of the slope reduces the displacement of the slope face as well as settlement under footing with notable reduction. The system provides an economic, practical and effective method for slope stabilization.

Influence of degree of saturation on soil nail pull-out resistance in compacted completely decomposed granite fill

The nail–soil interface shear strength is a key parameter in the design and stability assessment of soil nailing systems. A number of factors will influence the nail–soil interface shear strength. Among these factors, the degree of saturation (Sr) of the soil is an important one especially for permanent soil nail structures. To study the influence of Sron soil nail pull-out shear resistance, a series of laboratory pull-out tests have been conducted on soil nails in compacted completely decomposed granite (CDG) fill prepared to different Sr. The tests were conducted using two specially designed pull-out boxes (with same specifications). In the near-saturated tests, a high Sr(about 98%) was achieved using two special features of the apparatus: a waterproof front cap and back-water pressure pipes at the bottom of the pull-out box. Test results showed that the nail–soil shearing plane migrated outwards into the soil when the Srof the soil increased. Also, peak pull-out strengths of soil nails were strongly influenced by the Srof the soil. Among the tested Sr, the highest values of peak pull-out shear strength were obtained at Srvalues between 50% and 75%.

Numerical Simulation of Pressure Grouting in Soil Nail Pull-Out Tests

Soil nailing is a widely used technique for stabilizing slopes and excavations. In all current design methods, the nail-soil interface shear strength, that is, the pull-out resistance of a soil nail is an important parameter which controls the design and safety assessment of the soil nailing system. The pressure grouting is a cost effective method for increasing the soil nail pull-out resistance and in turn improving the performance of the nailed structure. In this paper, a three dimensional (3-D) finite element (FE) model for pull-out tests is established and verified by comparing simulated results with measured data. This model is then used to simulate the effect of grouting pressure on the soil nail pull-out resistance.

Application of Innovative GFRP Pipe Soil Nail System in Hong Kong

The current method of soil nail construction in Hong Kong is both labour intensive as well as expensive and a search for new soil nail material is required. In the present pilot test, light weight high strength and high corrosion resistance GFRP pipe with Tube a’ Manchette grouting technique is used as soil nail instead of the conventional steel reinforcement. It is found that this material can be handled easily on site with difficult access. From extensive laboratory as well as field tests, it is demonstrated that this new soil nail technique has various advantages for use in Hong Kong and many developed cities. The field test results on this innovative soil nail will be discussed in this paper.

A Laboratory Device to Test the Pull-Out Behavior of Soil Nails

Abstract Soil nailing is an in situ soil reinforcing technique adopted for stabilizing existing slopes in Hong Kong and in many other countries and regions. For the design of a soil nail system, pull-out capacity of a soil nail is an important design parameter. Field pull-out tests are then carried out to verify the pull-out resistance assumed at the design stage. However, the pull-out capacity of a soil nail in the field is influenced by a number of factors, such as variation in the soil properties, variation in the installation procedures, types of soil nail, and stress levels. Thus, field testing has a number of limitations. To overcome the limitations, a new laboratory pull-out testing apparatus was developed to investigate the interface shear strength behavior of the soil nails and surrounding soil. A numerical analysis was carried out to assess the initial stress conditions in the laboratory pull-out test box. A series of laboratory pull-out tests was performed with a cement grouted nail in a Completely Decomposed Granite (CDG) soil. It is aimed at studying the influence of overburden pressure, soil degree of saturation, and surface roughness of soil nail on the interface shear strength. The results indicate that the curves for pull-out tests exhibit a significant peak and post-peak shear strength behavior. And the interface shear strength between the nail and soil is shown to be dependent on the normal stress, the soil degree of saturation, and the surface roughness of the nail. A correlation of the interface shear strength with major influencing factors is then derived for practice design applications. The findings in this study may be a useful reference for geotechnical engineering in soil nailing design and constructions and for better understanding of the soil nail pull-out performance in the soil.

Comparison of Interface Shear Strength of Soil Nails Measured by Both Direct Shear Box Tests and Pullout Tests

The shear stress–displacement behavior and ultimate shear strength at the interface between the cement–grout nail and surrounding soil are of practical importance in the design and safety assessment of a soil nail system. The most commonly adopted method to measure the interface shear strength of a soil nail is a pullout testing method. The current study attempts to investigate the interface shear behavior between the cement-grouted materials (soil nails) and a completely decomposed granite soil using both a large-size direct shear test apparatus and a laboratory pullout test apparatus. The laboratory testing procedures are briefly described. The main test results obtained are presented, followed by discussion on the shear behavior of the soil–grout interface. The interface shear behavior measured from both the interface shear tests and the pullout tests on the same soil tested in the same or a similar condition are compared and discussed. It is shown that the shear stress–displacement behavior of the soi...

Effects of 3D discrete soil nail inclusion on pull-out, with implications for design

To reduce computational requirements, soil nail systems are usually modelled in finite elements as plane-strain models in which discrete nails are ‘smeared’ as continuous plates. The interaction of adjacent nails across horizontal spacing is assumed to be perfect. Intuitively, the interaction decreases as the spacing increases. A 3D study using a numerical pull-out model attempts to quantify the effect of various parameters on this effect, and hence provides guidelines for the zones of influence of nails according to finite element analysis. The guidelines provide an insight into the extent to which 2D plane-strain analysis is acceptable. The results are compared with numerical analyses from a single-row soil nail problem, and with case histories, to indicate the validity of the guidelines. Pour réduire les calculs, les systèmes de cloutage de sol sont généralement modélisés en éléments finis sous forme de modèles plan-déformation dans lesquels des clous discrets sont ‘étalés’ en plaques continues. L'interaction des clous adjacents à travers un espacement horizontal est supposée parfaite. Cependant, de manière intuitive, l'interaction diminue à mesure que l'espacement augmente. Une étude tridimensionnelle utilisant un modèle numérique d'arrachage tente de quantifier l'effet des divers paramè tres sur cet effet et, de là, de donner des lignes directrices pour les zones d'influence des clous selon les analyses d'éléments finis. Les directives donnent un aperçu de la mesure dans laquelle l'analyse bidimensionnelle plan-déformation est acceptable. Nous comparons les résultats avec les analyses numériques effectuées sur un problème de clous de sol àun seul rang ainsi qu'avec des études de cas, pour indiquer la validité de ces directives.

Effect of constrained dilatancy on pull-out resistance of nails in sandy clay

Soil-nailing technology has been widely used for the support of excavations, and for slope stability. For the design of a soil-nailing system, the pull-out resistance of the individual nails is of paramount importance. In this study, from an objective of strengthening the ground for the preservation of historical kiln sites, a combined technology of chemical grouting and soil nailing called the ‘earth sewing technique’ is presented. Field and laboratory model scale pull-out tests have been conducted to investigate the mobilisation of pull-out force. Triaxial and direct shear tests were performed to investigate and interpret the ultimate bond stress of nails. It has been shown that water content influences the pull-out capacity of nails in unsaturated sandy clay, not only through shear strength parameters, but also through additional normal stress due to constrained dilatancy. La technologie de cloutage des sols a été largement utilisée pour soutenir les excavations et stabiliser les pentes. Pour la conception d'un système de cloutage de sol, la résistance à l'arrachage des clous individuels a une importance primordiale. Dans cette étude, nous présentons, avec pour objectif de renforcer un sol pour la préservation d'un site historique, une technologie de cimentation chimique et de cloutage combinée appelée ‘technique de couture terrestre’. Des essais d'arrachage sur le terrain et sur modèle de laboratoire à échelle ont été menés pour enquêter sur la mobilisation de la force d'arrachage. Des essais de cisaillement triaxiaux et directs ont été réalisés pour étudier et interpréter la contrainte d'adhérence ultime des clous. Nous avons montré que la teneur en eau influence la capacité d'arrachage des clous dans de l'argile sableuse non saturée non seulement à cause des paramètres de résistance au cisaillement mais aussi à cause de la contrainte normale additionnelle due à la dilatance contrainte.

A three-dimensional parametric study of the use of soil nails for stabilising tunnel faces

Abstract Applying an effective nailing system at a tunnel heading, not only improves the stability of the tunnel heading and limits deformation at the tunnel face, but it also reduces volume loss during excavation and hence reduces ground surface settlement. The effectiveness of a soil nail system is affected by many factors such as the diameter and stiffness of the nails. In this paper, a systematic parametric study was conducted to study the axial rigidity of a nail, E n A n , for improving the stability of tunnel headings and reducing ground movements in stiff clay. The parametric study involved a series of three-dimensional elasto-plastic coupled-consolidation finite element analyses. The stability of the tunnel face is improved with increasing E n A n . For a given nail density applied at the tunnel face, an optimum axial rigidity of the nail ( E n A n ) opt can be identified. The efficiency of the nailing system diminishes when ( E n A n ) opt is reached. The use of a soil nailing system reduces the magnitude of stress relief at the tunnel heading during excavation. Thus, this reduction of stress relief minimises the amount of soil yielding and excess pore water pressure generated in the soil around the tunnel heading.