Abstract
We have evaluated the frictional stress of ground anchor of compression type with a large diameter based on the pulling test.
The concluding remarks of these test results are as follows:
1) The relationship between the pull-out load and displacement at the anchor head is roughly linear till the pull-out of anchor. In addition, the frictional stress of the lower side of the fixed anchor develops, larger than that of the upper side in the process of loading. Finally they become equal at the time of pull-out.
2) Regardless of soil type, the displacement of fixed anchor at the time of pull-out is about 10mm. The relationship between the frictional stress and displacement can be approximated by a hyperbola according to Equation (4), and these expressions are largely similar except for silt rock.
3) Two failure patterns were observed: the frictional resistance reaches the limit or the bond resistance reaches the limit. When the bond stress is much lower than the value of the Formula (8), the former pattern was observed. While the value was equivalent to the value of the Formula (8), the latter pattern was observed.
4) When the ultimate friction stress is analyzed in relation to SPT-N value, the variation is very large. On the other hand, the ultimate friction stress is possible to be estimated accurately by using the value of yield pressure in borehole lateral load test in gravel and sand, and by using the undrained shear strength in hard clay and soft rock.
5) The bond resistance in gravel reaches the limit at the time of pull-out, and the residual bond stress is 1/3 of the ultimate value. On the other hand, the frictional resistance in silt rock reaches the limit at the time of pull-out, and the residual friction stress is 1/2 of the ultimate value and 1/2 of the value of undrained shear strength.
6) There was no sharp decline in pulling load in the case of friction failure. But a sharp decline was observed in the case of bond failure. Hence friction failure is desirable as a design consideration.
