## 4 Discussion  
In order to gain sufficient risk response time for the decision makers, the GPR model was used during the construction of the Luochongwei station, and a time series length of 5 days was selected for rolling prediction of deformation for the next 3 days. And the deformation prediction results were used as an information source to be fused by the method proposed in this paper in order to realize the early warning of underground pit collapse risk. The results are shown in Figure 9.  
(1) Analysis of actual early-warning results. Figure 9a-f represent the changes in early-warning results over time for different monitoring points. The pink bar indicates the actual early-warning level. The highest actual early-warning level of C1, C5, and C18 is yellow, the highest actual early-warning level of C11 and C15 is orange, and the highest actual early-warning level of C14 is alarm. This shows that the collapse risk of monitoring point C14 is the highest, followed by C11 and C15, and the collapse risk of C1, C5, and C18 is lower. For C14, it can be seen that from day 1 to day 11, the monitoring point is basically in a safe state, indicating that the risk at this point is in a controllable range and no early warning has occurred. From day 12 to day 18, the yellow early-warning status occurs, which indicates that the pit is beginning to have the possibility of unsafe deformation, and the operator should start to pay attention to the deformation situation and communicate it in a timely manner in the daily meeting. The actual early-warning level on day 19 to day 20 is orange, the alarm is triggered on day 21 and eliminated on day 22 to day 23 but is still in the orange early-warning state, indicating that there is a large potential risk of collapse and that immediate measures should be taken until the risk is reduced to a safe state before construction can continue. It is essentially in a safe condition from day 24 to day 40, indicating that the measures taken had a positive effect and that no deformation collapses occurred. After confirmation by the expert on-site inspection, it was found that the occurrence of the above early-warning status was due to the unloading of the pit excavation leading to a large bulge near the monitoring point C14, and there was a high probability of deformation of the supporting structure or a small-scale collapse, which was undesired and required immediate measures to be taken. Firstly, site operators should be evacuated immediately, as well as those in neighbouring units or dwellings that may be affected. Secondly, excavation should be stopped immediately and additional settlement monitoring points outside the pit should be installed. In addition, immediately after, backfilling with grout or backfilling until the settlement trend outside the pit converges should be performed, before it can be stopped, and then the rotary sprayer should be used and cement should be equipped to reinforce the soil. It can be seen that the early-warning level was reduced to safe on day 25, indicating the effectiveness of the response measures taken. For C11 and C15, there is a short time of orange. The C15 monitoring point was at a safe or yellow level from the 1 stday to the 20 th day. Orange early-warning appeared on the 21 st day and the 22 nd day, and it finally reduced to a safe level after on-site disposal. The C11 monitoring point was at a safe or yellow level from the 1 st day to the 18 th day. The orange early-warning appeared on the 19 th day and the 21 st day, and finally reduced to a safe level after on-site disposal. C11 and C15 were deformed due to excavation and unloading near the C14 measuring point. It can be seen from Figure 9c,e that they were quickly reduced to the safety level after on-site treatment. For C1, C5, and C18, there are only two early-warning levels of safety and yellow. Safety shows that the risk of each location is in a controllable state, there are no obvious early-warning signs, and the monitoring data are also in the normal range.