随着采掘向深部延伸，岩溶陷落柱已成为华北煤田矿井开采最隐蔽的致灾地质因素之一。柱壁角是描述陷落柱形态特征的重要指标之一。

以西山煤田上下煤层综采均切割过的265个岩溶陷落柱为数据源，通过分区、统计、函数构建、地质类比，挖掘西山煤田岩溶陷落柱柱壁角中蕴藏的地质信息，获得如下认识：(1) 西山煤田陷落柱平均柱壁角为84.29°，超50%的陷落柱柱壁角在85°~90°，平均柱壁角自西北到东南逐渐增大，从82.05°增大到87.57°。(2) 西山煤田陷落柱柱壁角与8号煤层揭露的陷落柱面积成反比，依据柱壁角与陷落柱面积大小关系，陷落柱划分为：充分塌陷陷落柱(90°~85°)、次充分塌陷陷落柱(<85°~81°)、不充分塌陷陷落柱(<81°)；对应的2号煤层陷落柱面积分别为<556、556~1 700、>1 700 m²，等效半径为<13.3、13.3~23.3、>23.3 m；对应的8号煤层陷落柱面积分别为<1 250、1 250~2 750、>2 750 m²，半径分别为<20、20~30、>30 m。充分塌陷陷落柱一般发育有柱顶空腔，柱体结构较为松散，可导通顶板裂隙水与柱顶空腔水，以及底板承压奥灰水，是西山煤田导水陷落柱的一种重要类型。

类比地质历史时期降雨量结果显示，具有“北柱南相”的西山煤田岩溶陷落柱，可能形成于气候湿热的古近纪渐新世时期，强烈的岩溶作用吸收了大气中的CO₂，并锁定在沉积区，可能是导致全球大气CO₂含量急剧降低的重要原因。

As coal mining expands into deep parts, karst collapse pillars have become one of the most concealed disaster-causing geological factors in coal mining from mines in North China. The pillar wall angle of a collapse pillar serves as an important index used to describe the morphology of the collapse pillar.

With 265 karst collapse pillars cut by the fully mechanized mining of the upper and lower coal seams in the Xishan coalfield as the data source, this study extracted the geological information contained in the pillar wall angles of karst collapse pillars in the Xishan coalfield through zoning, making statistics, function construction, and geological analogy, obtaining the following insights: (1) The collapse pillars in the Xishan coalfield exhibit an average pillar wall angle of 82.49°, with over 50% of them manifesting pillar wall angles ranging between 85° and 90°. Their average pillar wall angles increase gradually from 82.05° to 87.57° from northwest to southeast. (2) The wall angles of collapse pillars in the Xishan coalfield are inversely proportional to the areas of the collapse pillars revealed by the No. 8 coal seam. Based on this relationship, the collapse pillars can be categorized into completely collapsed pillars (90°‒85°), less completely collapsed pillars (85°‒81°), and incompletely collapsed pillars (< 81°). Correspondingly, collapse pillars in the No. 2 coal seam exhibit areas of < 556 m², 556‒1 700 m², and > 1 700 m² and equivalent radii of < 13.3 m, 13.3-23.3 m, and > 23.3 m. Furthermore, collapse pillars in the No. 8 coal seam have areas of < 1 250 m², 1250‒2750 m², and > 2 750 m² and equivalent radii of < 20 m, 20‒30 m, and > 30 m. The completely collapsed pillars generally exhibit cavities on their tops and loose structures, which can connect fracture water in the roofs to water in cavities on pillar tops and confined Ordovician limestone water in the floors. Therefore, completely collapsed pillars are significant hydraulically conductive collapse pillars in the Xishan coalfield.

The analogy with rainfall in the geological history reveals that the karst collapse pillars in the Xishan coalfield, exhibiting the characteristics of karst sinkholes and caves in southern China, might have been formed during the Paleo-Oligocene with hot humid climates. During this period, CO₂ in the atmosphere was absorbed due to intense karstification and was then locked in sedimentary areas. This might be an important reason for the sharp decrease in global CO₂ concentration in the atmosphere.