Effect of Wetting on the Pullout Resistance of Grouted Soil Nails

2012 ◽  
Vol 226-228 ◽  
pp. 1304-1307
Author(s):  
Jason Y. Wu ◽  
Jr Min Chang
Keyword(s):  
Fine Sand ◽  
Shear Resistance ◽  
Test Results ◽  
Pullout Capacity ◽  
Interface Shear ◽  
Soil Nails ◽  
Soaking Time ◽  
Pullout Resistance ◽  
Soil Nail ◽  
Pullout Tests

In this research, laboratory pullout tests were conducted on grouted soil nails to study the effect of wetting on the interface shear resistance between nail and soil during pullout. Deformed bars with equal size to the true soil nails were used as model nails. The soil used was silty fine sand collected at the site and prepared to a very dense condition. Rainfall infiltration was simulated using duplicated soil nails inundated by water for different periods. Test results indicated that the peak pullout resistance strongly decreases upon wetting, with a reduction of about 60% after soaking for 28 days. However, the experiments showed that there is a threshold water content (or soaking time) beyond which the effect of infiltration on the pullout resistance is reduced. The laboratory protocols developed in this study offered an easy scheme for the prediction of the pullout capacity of a grouted soil nail upon wetting.

Pullout resistance of single and double nails in a model sandbox

2003 ◽  
Vol 40 (5) ◽  
pp. 1039-1047 ◽  
Author(s):  
Yung-Shan Hong ◽  
Cho-Sen Wu ◽  
Shang-Heng Yang
Keyword(s):  
Surface Roughness ◽  
Unit Length ◽  
Test Surface ◽  
Roughness Factor ◽  
Test Results ◽  
Overburden Pressure ◽  
Soil Nails ◽  
Pullout Resistance ◽  
Soil Nail ◽  
Group Efficiency

Pullout tests on single and double soil nails were conducted in a model sandbox. The test parameters included variations in the surface roughness, the ratio of nail length to nail diameter, the overburden pressure, and the distance between two nails. The characteristic of a single asperity, the asperity number per unit length, and the ratio of the thread depth to the soil particle size were used to define the surface roughness factor. The test results showed that the apparent friction coefficients at the soil–nail interface were dependent upon the surface roughness of the nail. Group efficiency was used to evaluate the effectiveness of a nail when installed within a group. The test results showed that the group efficiency of a double-nail system was dependent upon the surface roughness factor and has a linear relationship with the nail distance until 100% efficiency is reached. The minimum required distance for 100% efficiency also varied with the surface roughness factor.Key words: apparent friction coefficient, group efficiency, pullout test, surface roughness factor.

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

2007 ◽  
Vol 44 (11) ◽  
pp. 1314-1328 ◽  
Author(s):  
Li-Jun Su ◽  
Terence C.F. Chan ◽  
Y.K. Shiu ◽  
Tony Cheung ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Degree Of Saturation ◽  
Interface Shear Strength ◽  
Interface Shear ◽  
Soil Nails ◽  
Soil Nail ◽  
Pull Out ◽  
Decomposed Granite ◽  
Soil Interface ◽  
Completely Decomposed Granite

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 Sr on 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 Sr of the soil increased. Also, peak pull-out strengths of soil nails were strongly influenced by the Sr of the soil. Among the tested Sr, the highest values of peak pull-out shear strength were obtained at Sr values between 50% and 75%.

Experimental investigation of compaction-grouted soil nails

2017 ◽  
Vol 54 (12) ◽  
pp. 1728-1738 ◽  
Author(s):  
Qiong Wang ◽  
Xinyu Ye ◽  
Shanyong Wang ◽  
Scott William Sloan ◽  
Daichao Sheng
Keyword(s):  
Large Scale ◽  
Scale Model ◽  
Interface Shear ◽  
Soil Nails ◽  
Soil Nail ◽  
Pull Out ◽  
Grouting Pressure ◽  
Large Scale Model ◽  
Ultimate Failure ◽  
Surrounding Soil

An innovative compaction-grouted soil nail was designed by injecting grout into a special latex balloon (grouting bag) to avoid bleeding and penetration of grout into the surrounding soil. A series of large-scale model tests was performed to study the surrounding soil responses due to grouting and the subsequent pull-out resistance of the soil nail. The experimental results show that grouting pressure plays an important role in the enhancement of the density and (or) strength of the surrounding soil. In addition, during the pull-out process, the compaction-grouted soil nail exhibits a strain-hardening behaviour without a yield point. This is a significant advantage of this new soil nail, indicating that it can enable soil masses to remain stable against a relatively large deformation before ultimate failure. The main factors behind the improvement of the pull-out resistance of the new soil nail are, first, the compaction–densification of the soil near the grouting bag due to grouting, resulting in the enhancement of the shear strength of the soil, and, second, the enlargement of the grouting bag, causing the increase of the interface shear and end resistance to the pull-out of the soil nail.

The Influence of Geometric Structure of Geogrids on the Pullout Resistance

2011 ◽  
Vol 261-263 ◽  
pp. 586-590
Author(s):  
Di Wu ◽  
Chao Xu
Keyword(s):  
Geometric Structure ◽  
Geometric Characteristic ◽  
Test Results ◽  
Pullout Force ◽  
Unresolved Problem ◽  
Pullout Resistance ◽  
Reinforced Soils ◽  
Pull Out ◽  
Pullout Tests

The influence of geometric characteristic of geogrid on pullout behavior is still an unresolved problem in the application of geosynthetic reinforced soils. The laboratory pullout tests were employed to investigate the effects of geometric structure features on the pull-out test results. The results of this study indicate that the effect of geometric structure on pullout behavior is reflected in two aspects: geogrid type and mesh form of geogrid. The variation of geogrid types can lead to the changes of the pullout force and pullout modulus. For the latter one, the reduction of longitudinal and transverse geogrid ribs not only causes the decrease of friction and transverse rib bearing resistance, but also changes the mesh form which is the geometric structure of grids.

Experimental study on the pullout resistance of pressure-grouted soil nails in the field

2013 ◽  
Vol 50 (7) ◽  
pp. 693-704 ◽  
Author(s):  
Cheng-Yu Hong ◽  
Jian-Hua Yin ◽  
Hua-Fu Pei ◽  
Wan-Huan Zhou
Keyword(s):  
Water Content ◽  
Field Tests ◽  
Soil Samples ◽  
Soil Nails ◽  
Pullout Resistance ◽  
Soil Nail ◽  
Grouting Pressure ◽  
Overburden Stress ◽  
Drill Holes ◽  
Surrounding Soil

The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet fully understood. In this study, a series of tests was conducted to evaluate the pullout response of grouted soil nails in a field slope. A new innovative grouting packer system was developed to control the grouted length and maintain the cement grout pressure of the grouted part. By using the grouting packer system, a total of 10 soil nails placed at different soil depths were grouted with different pressures in the field. The pullout results of present field tests and a number of past laboratory tests indicate that the apparent coefficient of friction (ACF) decreases with the increase of overburden stress even though grouting pressure is applied. In addition, when the overburden stress is unchanged, the obtained ACF values in the field tests appear to increase almost linearly with the increase of grouting pressure. After the soil nails were completely pulled out of the ground, the surfaces of the soil nails and surrounding soil were examined. It is found that the water content of the soil samples at the soil–nail interfaces decrease substantially compared to the water content of soil samples in drill holes. Measurement results also show that the failure surfaces of soil nails shifted about 16 mm on average into the surrounding soil due to the application of grouting pressure.

Laboratory study on pullout capacity of helical soil nail in cohesionless soil

2017 ◽  
Vol 54 (10) ◽  
pp. 1482-1495 ◽  
Author(s):  
M. Sharma ◽  
M. Samanta ◽  
S. Sarkar
Keyword(s):  
Double Helix ◽  
Test Procedure ◽  
Failure Criteria ◽  
Cohesionless Soil ◽  
Pullout Capacity ◽  
Overburden Pressure ◽  
Soil Nails ◽  
Dense Sand ◽  
Soil Nail ◽  
Different Types

Helical nails are a new alternative to conventional soil nails or tie-backs for stabilization of slopes, excavations, and embankments due to ease of installation, minimal site disturbance, and immediate loading capability. Pullout capacity of helical nails is a critical parameter for their design. This study investigates the pullout behaviour of helical soil nails installed in dry dense sand through a series of laboratory tests. The tests were performed on seven different types of helical nails in a displacement-controlled manner. The paper describes the test procedure, results and highlights the influence of different parameters on the pullout capacity. Results show that roughness of the nail shaft significantly influences the peak pullout capacity of helical soil nails. A linear relationship between peak pullout force and overburden pressure is observed for different types of helical soil nails, indicating that it satisfies the Mohr–Coulomb failure criteria. A helical soil nail having a double helix of unequal diameter and the same interspacing shows higher pullout capacity than a helical soil nail having a double helix of the same diameter. The position of the helix and spacing-to-diameter ratio of the soil nail with a double helix of unequal diameter plays a significant role on the peak pullout capacity.

Tilt Table Test for Interface Shear Resistance Between Flowlines and Soils

2003 ◽  
Author(s):  
Shadi S. Najjar ◽  
Robert B. Gilbert ◽  
Eric A. Liedtke ◽  
Bill McCarron
Keyword(s):  
Shear Resistance ◽  
Test Method ◽  
Shear Stresses ◽  
Test Results ◽  
Tilt Table Test ◽  
Tilt Table ◽  
Interface Shear ◽  
Effective Normal Stress ◽  
System A ◽  
Loading System

This paper describes a tilt table test method for measuring the shear resistance between flowlines and supporting soils. This shear resistance is important in considering buckling and walking in the design of flowlines. A significant challenge in measuring the shear resistance is the very low effective normal stresses that exist at the interface in field conditions. Since the measured stresses will be small, even small amounts of friction in a test device can adversely affect the results. The tilt table method overcomes this problem by using gravity to apply the normal and shear stresses to the soil-flowline interface, eliminating the need for a mechanical loading system. A set of test results is presented to demonstrate how the test method can be used to measure the resistance between the flowline and the soil. These results illustrate that the type of flowline coating and the effective normal stress affect the shear resistance.

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