in situ tbm penetration tests and rock mass boreability analysis in hard rock tunnels

Drilling is a generally adopted way to express how difficult it is for a tunnel drill to penetrate a rock.
Since the drillability is related to the nature of the rock, the specifications of the boring machine and the operating parameters of the boring machine, an accurate definable quantity has not been obtained so far.
In order to analyze and compare the drillability of rock, a series of tunnel shield friction tests were carried out at a tunnel excavation site.
In the process of rock tunnel excavation, two sets of rock tunnel excavation tests were carried out under different rock quality conditions.
In each step of the penetration test, the rock muck is collected for slag sieve analysis and the shape of large fragments is measured to analyze the effectiveness of TBM crushing under different tool thrust.
The results show that there is a critical point in the penetration curve.
When the thrust of each knife is higher than the critical value, the penetration rate of each revolution speed will increase rapidly with the increase of the thrust of each knife.
The results of slag sieve analysis show that with the increase of thrust, the size of slag increases and the rock crushing efficiency improves.
The muck becomes good when the thrust is greater than the critical value-graded.
The results of the muck shape analysis also show that the chip shape changes from flat to fine and flat as the thrust increases.
The boreable index at the penetration critical point of 1mm/rev
A new index is proposed to evaluate the North property of rock mass.