# Mechanism of Mining-Induced Dynamic Loading in Shallow Coal Seams Crossing Moaling Terrain
## 6 Engineering Case Validation
### Dynamic Variation Patterns of Support Loads  
To investigate the dynamic variation of the support load during mining through the Maoliang terrain, the above parameters are substituted into Equation (10), and the dynamic variation of the support load during mining through the Maoliang terrain is shown in Figure 10.  
As shown in Figure 10, it can be observed that as the working face advances, there is a significant difference in the variation trend between the support load and the Maoliang terrain load, showing a lag in the support load response. Before entering the Maoliang terrain zone, the support load is 7237 kN per support. When the working face advances 25 m into the Maoliang terrain zone, the support load gradually increases, reaching a peak value of 9266 kN per support at 125 m, which is a 28.04% increase compared to the pre-entry load. At this point, the peak position of the support load lags behind the peak Maoliang terrain load by approximately 25 m. As the working face further advances 25 m beyond the Maoliang terrain zone, the support load gradually decreases and returns to its original level. These results indicate that the Maoliang terrain load has a significant impact on the support load and exhibits a lag effect with a lag distance of approximately 25 m.  
The lag phenomenon is closely related to the interaction mechanism between the surface soil layer and key bedrock strata, which is manifested in the following three ways:  
1. Spatiotemporal differences in key stratum fracturing  
In the Maoliang terrain zone, the thick surface soil layer transfers its self-weight load to the working face through an upper key stratum. Due to the large span and high flexural stiffness of the upper key stratum, more strain energy must accumulate before fracturing, causing its fracturing position to lag behind that of the lower key stratum. The lower key stratum fractures earlier, forming a \"step rock beam\" structure, while the \"hinged masonry  
Figure 10: Dynamic variation of support loads during mining across the Maoliang terrain.  
beam\" structure formed by the fractured upper key stratum gradually transfers the soil layer load to the supports. This results in the peak support load responding later than the peak Maoliang terrain load.
2. Synergistic deformation effect between soil and bedrock  
The surface soil layer has low mechanical strength and cannot bear loads independently, relying on the deformation of the key bedrock strata. When the upper key stratum starts to rotate and subside, the soil layer deforms synchronously with the key stratum blocks, forming a \"surface soil-key stratum synergistic deformation body\". The time lag between the compressive deformation of the soil layer and the fracture displacement of the key stratum introduces a delay in the load transfer.
3. Hierarchical adjustment of stress transfer paths  
Before entering the Maoliang zone, the support loads primarily originated from fracturing of the immediate roof and lower key strata. After entering the zone, the stress transfer path transforms into a multi-level mode: \"surface soil layer \(\rightarrow\) upper key stratum \(\rightarrow\) lower key stratum \(\rightarrow\) supports\". Following the fracture of the upper key stratum, loads are transmitted gradually through contact stresses at the articulated joints between blocks rather than direct vertical loading, causing delays in stress wave propagation. Additionally, the parabolic load distribution of the Maoliang terrain (with higher central loads and lower lateral loads) causes the middle of the key stratum to reach the fracturing strength first, and the time required for fracturing to propagate laterally further exacerbates the lag in load transfer.