- Title
- Experimental study of pressure grouted soil nail system
- Creator
- Bhuiyan, Mohammad Zahidul Islam
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Soil nailing is a reinforcement technique, used to reinforce in situ ground to stabilize it more effectively and economically, in which the reinforcing slender elements (typically steel bars), called soil nails, are inserted into a soil mass by different installation methods such as driving, jacking or pre-drilling. The nailing technique is extensively applied for slopes, excavations and retaining walls. Conventionally, frictional soil nails (e.g., driven, drilled and grouted nails) are commonly used in practice, based on the soil conditions, project cost and construction flexibility, and the pullout resistance of the frictional nails primarily comes from the frictional resistance developed at the nail/soil (driven nail) or grout/soil interface (drilled and grouted nail). The frictional soil nails do not show any end bearing resistance and, thus, soil-nailed structures have the potential to undergo a relatively large lateral deflection after construction. Therefore, the frictional resistance is considered an important parameter for the design and safety assessment of conventional soil-nailed structures. In soil nailing practice, primarily, this parameter is still evaluated using field-based experience rather than a detailed scientific knowledge of nail-soil interactions. Nowadays, pressure grouting is being progressively used for soil nailed structures as an alternative to the frequently used conventional gravity/low pressure grouting, since this grouting technique has the ability to increase the bond strength significantly, which in turn increases the pullout resistance of a grouted soil nail. The objective of this research is to develop a reliable and efficient method for enhancing the pullout resistance of soil nails through experimental research. This thesis concentrates on the experimental study of pressure-grouted anchor-type nail systems, which are being developed in the Priority Research Centre for Geotechnical Science and Engineering, The University of Newcastle, Australia. To conduct the fully instrumented experimental study, a new volume-controlled injection system was developed and the existing apparatus was redesigned and modified for pullout testing of the pressure-grouted nail system. The physical model study was comprised of three test groups. The underlying objective of Group 1 was to evaluate the effects of grout injection rates on the pressure-grouted soil nail system. To assess the grouting rate effects on the grout injectability and the pullout resistance of the pressure-grouted soil nail, pressurized grout (w/c = 0.50) was injected through the pre-buried soil nail by the newly developed volume-controlled injection pump at different injection rates, viz. 4.0 L/min, 5.0 L/min, and 6.5 L/min. Note that a latex membrane was used as a liner around the grouting outlets of the pre-buried hollow nail to form a Tube-a-Manchette (TAM) for direct injection of grout into the surrounding soil, simulating compaction grouting, which resulted in the formation of a grout bulk around the outlets (injection points). The results obtained from this experimental study (Group 1) revealed that the volume of injected grout (i.e., grout penetration) increased as the injection rates increased, and thus the pullout resistance of the pressure-grouted soil nail also increased with the injection rate. It was found that the pullout resistance of the nail was governed by the injected grout volume rather than the injection pressure and the grouted nail acted as an anchor, showing a significant strain-hardening behaviour in pullout resistance. In addition, the results indicated that the expulsion (seepage) of water from the pressurized neat cement grout was directly and proportionally related to the injection rate, i.e., the higher the injection rate, the higher the seepage of water. In the case of Group 2, a series of fully instrumented physical model tests were conducted to evaluate the performance of the grout, including its bleeding resistance, propagation and pressure transfer mechanism into the surrounding soil under pressurized injection conditions. Like Group 1, a pre-buried soil nail with a Tube-a-Manchette (TAM) facility was used for direct injection of the pressurized additive-mixed grout into the soil surrounding the nail to evaluate the grout-soil interaction in sand. As a grouting fluid, three different grout compositions with water/solid (cement + additive) ratio (w/s) varying from 0.30 to 0.50 were used and the performances of these grouts were compared with a traditionally used neat cement grout (w/c = 0.50). The results of Group 2 indicated that addition of an additive (a blend of superplasticizers and suspension agents) in a neat grout mix decreased the viscosity of the grout significantly by reducing the agglomeration tendency of the cement particles in suspension. The viscosity of the cementitious grout increased exponentially as the water solid (w/s) ratio decreased, whereas fluidity increased by increasing the w/s ratio. Consequently, the injectability (penetration) of the grout into a soil mass increased with decreases in viscosity of the injecting grouts. Furthermore, it was found that the volume of grout injected not only influenced the pullout capacity of pressure-grouted nails but the shape of the bulb formed inside the compacted fill also affected this type of nail performance, since highly fluid grouts (e.g., w/s = 0.40 and 0.50) formed irregular grout bulbs (deformed bulbs) that failed easily due to the stress concentration at a very small pullout displacement without mobilizing its maximum pullout capacity for a specified grout volume. Therefore, an additive-mixed cementitious grout of w/s ratio 0.30 was suggested as an effective and alternative grouting fluid compared with the conventional neat grout (w/c = 0.50) for the pressure grouted nail system because of its high bleed resistance, high compressive strength, high bond strength, low shrinkage and high fluidity. Based on the performance of the pressure-grouted (pre-buried) soil nail with and without an additive-mixed grout (Test groups 1 and 2), an innovative driven and grouted soil nail (termed here the x-Nail) was designed and developed. The innovative x-Nail is a hybrid soil nail that introduces compaction grouting in a purely frictional driven nail. The innovative design makes it possible to drive the x-Nail into in situ ground, together with a latex balloon that is used for compaction grouting in order to form a grout bulb at the driven end of the nail to improve its pullout resistance. The ultimate objective of Group 3 was to investigate the performance of a newly developed driven and grouted soil (termed here the x-Nail) compared to a conventional driven soil nail (purely frictional nail). For compaction grouting, a special type of additive-mixed cement grout (w/s = 0.30) was used because of its zero bleeding and high bond strength, which was injected by the developed volume-controlled injection system to control injection volume. The pullout testing results of the innovative x-Nail showed that the pullout capacity of the grouted x-Nail was much higher compared with the conventional driven (purely frictional) soil nail. The pullout force of the grouted driven nail increased almost linearly with increases in diameter of the grout bulb (i.e., the larger the bulb diameter, the higher the pullout force), since the grout bulb provided a significant amount of end-bearing resistance that resulted from the passive resistance of the soil situated in front of the bulb. Almost 90% of pullout force was resisted by the expanded grout bulb. Consequently, the grouted x-Nail worked as an anchor instead of a frictional nail and showed a displacement-hardening behaviour in pullout force. Overall, it could be said that the x-Nail is a promising alternative means of soil reinforcement, which might be capable of withstanding a relatively large deformation before failure.
- Subject
- soil nail; compaction grouting; pullout force; pressure grouting; laboratory test; Injection rate; zero bleeding grout
- Identifier
- http://hdl.handle.net/1959.13/1415529
- Identifier
- uon:36917
- Rights
- Copyright 2020 Mohammad Zahidul Islam Bhuiyan.
- Language
- eng
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