Evaluation of heavy roller compaction on a large-thickness layer of subgrade with full-scale field experiments

Abstract

Subgrade construction is frequently interrupted due to precipitation, soil shortage, and environmental protection. Therefore, increasing the thickness layer is required to reduce construction costs and to allow highways to be placed into service earlier. This paper presents a series of full-scale field experiments evaluating the compaction quality of gravel subgrade with large-thickness layers of 65 cm and 80 cm using heavy vibratory rollers. An improved sand cone method was first proposed and calibrated to investigate the distribution of soil compaction degree across the full subgrade depth. Results showed that dynamic soil stresses caused by the heavy vibratory rollers were 2.4–5.9 times larger than those of traditional rollers, especially at deeper depths, which were large enough to densify the soils to the full depth. A unified empirical formula was proposed to determine the vertical distribution of dynamic soil stresses caused by roller excitation. It was demonstrated that soils were effectively compacted in a uniform fashion with respect to the full depth to 96.0%–97.2% and 94.1%–95.4% for the large-thickness layers of 65 cm and 80 cm within 6 or 7 passes, respectively. Empirically, linear formulae were finally established between soil compaction degree and the subgrade reaction modulus, dynamic modulus of deformation, dynamic deflection, and relative difference of settlement to conveniently evaluate the compaction qualities. It is demonstrated that increasing the thickness layer by means of heavy rollers can significantly reduce the cost and time burdens involved in construction while ensuring overall subgrade quality. 目的 本文旨在通过65 cm和80 cm松铺厚度路基的全比尺现场试验，提出保障大厚度路基压实效果的施工工艺和评价方法，以提高路基填筑的施工效率、降低能耗和碳排放。 创新点 1. 改进适用于大厚度路基压实度评价的灌砂法；2. 建立碾压轮载作用下的路基内部动态土压力计算修正方程；3. 提出大厚度路基压实施工工艺及验收指标与压实度的关联关系，对大厚度路基压实质量进行可靠快速评价。 方法 1. 采用改进的灌砂筒及其标定方法，对大厚度路基的压实度进行分层检测；2. 基于现场土压力分层监测，获得碾压机械作用下动态土压力沿路基深度的衰减规律；3. 通过对每一遍碾压后的压实度、沉降差、K30、动态回弹模量、动弯沉进行多点检测和分析，获得各物理力学指标随碾压遍数的变化规律及其相互关联关系。 结论 1. 高能级压实下的65 cm和80 cm松铺厚度路基动土压力可达0.19∼1.18 MPa和0.079∼1.19 MPa，可采用修正后的Boussinesq方程表达；2. 路基压实效果与应力水平和土层下部支撑密切相关，底层土体压实度提升前上层土体难以致密化；3. 高能级碾压机械可保证大厚度路基全深度有效压实，且动弯沉作为大厚度路基压实质量评价指标更为可靠。