A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
A modified NX-borehole jack with flexible loading platens
https://orcid.org/0000-0002-6121-3179
Abstract The NX borehole jack test is the most widely used method to determine the deformation modulus of rock mass in the field. The common borehole jack, also known as the Goodman jack, has two drawbacks. The first is that the bending of the platens induces extra values in the displacement gauges (LVDTs), which causes the calculated modulus to be smaller than the actual figure. The second drawback is the demand for a perfect rock/platen contact. A new modified borehole jack has been designed in the present research, which overcomes the drawbacks of the Goodman jack. The new jack incorporates three improvements: (1) LVDTs located in the middle of the jack, (2) flexible platens for full rock/platen contact, (3) a pressure sensor installed at the end of the jack for accurate loading pressure measurement. A detailed theoretical analysis was carried out for the new jack, and experiments on blocks of concrete and sandstone were performed to verify the viability of the conception. The preliminary results suggest that the modified jack has a good theoretical basis, and may lower test requirements for borehole preparation. The process of borehole jack testing was simulated under plane strain conditions. The results indicate that the rock/platen contact condition of the Goodman jack varies with the modulus of rock and the loading pressure, while the contact state of the modified jack is insensitive to the modulus of the rock. The precisions of the jacks were also analyzed. The results show that the precision of the jack is acceptable when the loading pressure is over 30MPa; however, when the modulus of rock is estimated to be over 65GPa, the precisions of the Goodman and modified jack are both quite low.
Highlights The drawbacks of Goodman jack are discussed. A modified jack with flexible loading platen is proposed. Detailed analysis of the modified jack is conducted based on elastic theory. The precisions of the Goodman and modified jack are analyzed.
A modified NX-borehole jack with flexible loading platens
https://orcid.org/0000-0002-6121-3179
Abstract The NX borehole jack test is the most widely used method to determine the deformation modulus of rock mass in the field. The common borehole jack, also known as the Goodman jack, has two drawbacks. The first is that the bending of the platens induces extra values in the displacement gauges (LVDTs), which causes the calculated modulus to be smaller than the actual figure. The second drawback is the demand for a perfect rock/platen contact. A new modified borehole jack has been designed in the present research, which overcomes the drawbacks of the Goodman jack. The new jack incorporates three improvements: (1) LVDTs located in the middle of the jack, (2) flexible platens for full rock/platen contact, (3) a pressure sensor installed at the end of the jack for accurate loading pressure measurement. A detailed theoretical analysis was carried out for the new jack, and experiments on blocks of concrete and sandstone were performed to verify the viability of the conception. The preliminary results suggest that the modified jack has a good theoretical basis, and may lower test requirements for borehole preparation. The process of borehole jack testing was simulated under plane strain conditions. The results indicate that the rock/platen contact condition of the Goodman jack varies with the modulus of rock and the loading pressure, while the contact state of the modified jack is insensitive to the modulus of the rock. The precisions of the jacks were also analyzed. The results show that the precision of the jack is acceptable when the loading pressure is over 30MPa; however, when the modulus of rock is estimated to be over 65GPa, the precisions of the Goodman and modified jack are both quite low.
Highlights The drawbacks of Goodman jack are discussed. A modified jack with flexible loading platen is proposed. Detailed analysis of the modified jack is conducted based on elastic theory. The precisions of the Goodman and modified jack are analyzed.
A modified NX-borehole jack with flexible loading platens
https://orcid.org/0000-0002-6121-3179
Abstract The NX borehole jack test is the most widely used method to determine the deformation modulus of rock mass in the field. The common borehole jack, also known as the Goodman jack, has two drawbacks. The first is that the bending of the platens induces extra values in the displacement gauges (LVDTs), which causes the calculated modulus to be smaller than the actual figure. The second drawback is the demand for a perfect rock/platen contact. A new modified borehole jack has been designed in the present research, which overcomes the drawbacks of the Goodman jack. The new jack incorporates three improvements: (1) LVDTs located in the middle of the jack, (2) flexible platens for full rock/platen contact, (3) a pressure sensor installed at the end of the jack for accurate loading pressure measurement. A detailed theoretical analysis was carried out for the new jack, and experiments on blocks of concrete and sandstone were performed to verify the viability of the conception. The preliminary results suggest that the modified jack has a good theoretical basis, and may lower test requirements for borehole preparation. The process of borehole jack testing was simulated under plane strain conditions. The results indicate that the rock/platen contact condition of the Goodman jack varies with the modulus of rock and the loading pressure, while the contact state of the modified jack is insensitive to the modulus of the rock. The precisions of the jacks were also analyzed. The results show that the precision of the jack is acceptable when the loading pressure is over 30MPa; however, when the modulus of rock is estimated to be over 65GPa, the precisions of the Goodman and modified jack are both quite low.
Highlights The drawbacks of Goodman jack are discussed. A modified jack with flexible loading platen is proposed. Detailed analysis of the modified jack is conducted based on elastic theory. The precisions of the Goodman and modified jack are analyzed.
A modified NX-borehole jack with flexible loading platens
Zhang, Kai (author) / Hou, Rongbin (author) / Gamage, Ranjith Pathegama (author)
Engineering Geology ; 209 ; 152-162
2016-05-28
11 pages
Article (Journal)
Electronic Resource
English
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