Abstract
The formation process of EDZs (excavation damaged zones) in the roadways of deep underground mines is complex, and this process is affected by blasting disturbances, engineering excavation unloading, and adjustment of field stress. The range of an excavation damaged zone (EDZ) changes as the time and space change. These changes bring more difficulties in analyzing the stability of the surrounding rock in deep engineering and determining a reasonable support scheme. In a layered rock mass, the distribution of EDZs is more difficult to identify. In this study, an ultrasonic velocity detector in the surrounding rock was used to monitor the range of EDZs in a deep roadway which was buried in a layered rock mass with a dip angle of 20–30°. The space-time distribution laws of the range of EDZs during the excavation process of the roadway were analyzed. The monitoring results showed that the formation of an EDZ can be divided into the following stages: (1) the EDZ forms immediately after the roadway excavation, which accounts for approximately 82%–95% of all EDZs. The main factors that affect the EDZ are the blasting load, the excavation unloading, and the stress adjustment; (2) as the roadway excavation continues, the range of the EDZs increases because of the blasting excavation and stress adjustment; (3) the later excavation zone has a comparatively larger EDZ value; and (4) an asymmetric supporting technology is necessary to ensure the stability of roadways buried in layered rocks. Additionally, the predictive capability of random forest modeling is evaluated for estimating the EDZ. The root-mean-square error (RMSE) and mean absolute error (MAE) are used as reliable indicators to validate the model. The results indicate that the random forest model has good prediction capability (RMSE = 0.1613 and MAE = 0.1402).
Highlights
Eoretical analysis, numerical simulations, and field tests are commonly used to predict the size of an excavation damage zone (EDZ) in underground engineering. eoretical analyses are based mainly on different constitutive models and failure criteria, such as Mohr–Coulomb and Hoek–Brown failure criteria [19], which do not consider the effect of intermediate principal stress on EDZs. e Drucker–Prager criterion and unified strength theory have been used to solve the elasticplastic problem of surrounding rocks in underground roadways [20, 21]
Numerical simulation and field testing are two effective methods in the stability analysis of rock engineering [22,23,24,25] that have been widely applied to investigate the distribution ranges of EDZs. e size of an EDZ is a function of time and moisture and has a significant effect on its development, which is affected by rock mass structure, initial stress, and tunnel radius [26,27,28,29]
To validate the predictive models based on the predicted and measured values, 16 testing samples were validated by the optimized random forest model. e results are presented in Figure 13 and show actual vs. predicted EDZ by linear regression and random forest algorithm using the test data
Summary
The size of the EDZs in different sections, in order from the largest to the smallest, is as follows: Section 3, Section 2, and Section 1, as shown in Figure 9. e order of the EDZ size is opposite of the excavation order of the sections. Us, based on the distribution regular of the EDZ, the supporting technology was modified as follows: the length of the bolts was changed from 2.0 m to 2.5 m at the top left corner and the lower left corner of the roadway and the length of bolts was kept at 1.5 m at the other positions. After these changes, the occurrence of roof caving and floor heaving was reduced
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