Hydro-Mechanical Batch Processing in Ancient Deep Excavation (ca. 200 BCE): An Engineering Deconstruction of the Longyou Caves

Abstract

*Added: Chapter 3.7: Micro-Drainage and the Morphological Evolution of Swelling Scars The Longyou Caves in Zhejiang Province, China, present a profound archaeological and architectural anomaly: a complex of 24 massive subterranean caverns carved into argillaceous siltstone, with an estimated extraction volume exceeding one million cubic meters. Despite the monumental scale and strict structural tolerances of the site, there is a complete absence of historical documentation and regional spoil heaps. While prevailing theories frequently classify the caverns as ceremonial palaces, elite tombs, or covert military garrisons, these models struggle to reconcile with fundamental geomechanical and logistical constraints. This paper proposes a paradigm shift, hypothesizing that the complex functioned not as an architectural end-product, but as a highly optimized, industrial-scale subterranean quarry designed for the mass extraction of raw material for regional hangtu (rammed earth) mega-projects. Through the application of structural engineering, hydrogeology, and rock mechanics, a cohesive operational model is introduced. We propose a top-down, hydro-mechanical batch-extraction methodology: the controlled, cyclical flooding of strictly horizontal working floors utilized meteoric water (monsoon rainfall) to systematically weaken the rock's structural cohesion via hydration and clay-mineral swelling (slaking). The natural lithostatic pressure of the bedrock prevented structural failure by sealing the load-bearing pillars against moisture penetration. This localized hydro-mechanical softening permitted efficient, dust-free manual scraping layer by layer, thereby recontextualizing the prominent horizontal step-terraces and fine parallel striations across the cavern walls as residual water-level markers and specific ergonomic tool-path geometries, rather than decorative motifs. Furthermore, to account for the consistently narrow 50-centimeter partition walls separating isolated chambers, we hypothesize the utilization of precise surface macro-grid mapping combined with vertical plumb-line projection to maintain absolute geometric alignment during the top-down descent. Finally, the isolated ornamental reliefs found exclusively in Cave 1 are re-evaluated. Rather than indicating a primary ceremonial purpose for the entire complex, they are proposed to act as an administrative hallmark or imperial seal denoting the commissioning authority, providing a logical anchor for the Han Dynasty dating. By replacing conventional architectural assumptions with rigid mechanical, hydrological, and logistical imperatives, this theoretical framework offers a physics-based, highly probable explanation for the construction, rapid operational lifespan, and subsequent abandonment of the Longyou complex.