Causes of arch expansion and anti-arching design method for cement-stablized base layer in arid desert regions of northwest China

To address the severe arch expansion that has emerged in recent years in cement-stablized base layers in the arid desert regions of northwest China, passive prevention measures were conventionally applied. With the cement-stablized base layers exhibiting arch expansion in multiple sections of Xinjiang as research objects, by combining field investigations, laboratory tests, and theoretical analysis, core samples from both arched and non-arched sections of the base and subgrade were drilled to test their physicochemical properties, mechanical strength, microscopic morphology, and phase composition. Controlled laboratory expansion tests under multiple factors were conducted, and the anti-arching effect was verified through water-heat-salt multi-field coupling tests on optimized materials and structures to systematically elucidate the multi-field coupling disaster mechanism of arching in cement-stablized base layers. Accordingly, a set of integrated optimization design methods for materials and structures was proposed for active prevention. Research results indicates that the arch expansion in cement-stablized base layers in the northwestern saline soil regions is triggered by the coupled effects of "water-heat-salt" factors. The fundamental mechanism lies in the chemical reaction between sulfate ions (with contents 1.5-3.6 times the limit specified in the Technical Guidelines for Construction of Highway Roadbases (JTG/T F20—2015)) and cement hydration products, generating expansive substances such as ettringite and gypsum. This leads to an average reduction of 59.74% in the compressive strength of the base layers, while high temperatures significantly accelerate salt migration and reaction processes. The active prevention and control method centered on "salt control, temperature reduction, cement reduction, and structural adjustment" indicates that material optimization is the key. Using large-grade (37.5 mm) and extra-large-grade (53 mm) base layers with low cement content reduces expansion deformation by 12.12% and 27.27%, respectively. The installation of a graded crushed stone insulation layer reduces the expansion strain at the top of the base layer by approximately 83%. A graded gravel interception layer effectively blocks capillary water-salt migration and reduces salt enrichment concentration from 5.1% to 3.9%. For generally low-salt, extremely high temperature, medium-to-high saline soil, and high-salt-high-temperature composite regions, the combinations of anti-arching base layer, anti-arching base layer + insulation layer, interception layer + anti-arching base layer, and insulation layer + anti-arching base layer + interception layer are recommended, respectively. This achieves targeted, zonal, and categorized prevention and control from mechanism to practice.