Numerical simulation of intelligent compaction for subgrade construction

During the compaction of a road subgrade, the mechanical parameters of the soil mass change in real time, but current research assumes that these parameters remain unchanged. In order to address this discrepancy, this paper establishes a relationship between the degree of compaction K and strain ε. The relationship between the compaction degree K and the shear strength of soil(cohesion c and frictional angle φ) was clearly established through indoor experiments. The subroutine UMAT in ABAQUS finite element numerical software was developed to realize an accurate calculation of the subgrade soil compaction quality. This value was compared and analyzed against the assumed compaction value of the model, thereby verifying the accuracy of the intelligent compaction calculation results for subgrade soil. On this basis, orthogonal tests of the influential factors(frequency, amplitude, and quality) for the degree of compaction and sensitivity analysis were carried out. Finally, the ‘acceleration intelligent compaction value’, which is based on the acceleration signal, is proposed for a compaction meter value that indicates poor accuracy. The research results can provide guidance and basis for further research into the accurate control of compaction quality for roadbeds and pavements.

Mechanical behaviour analysis and support system field experiment of confined concrete arches

Soft rock control is a big challenge in underground engineering.As for this problem,a high-strength support technique of confined concrete(CC)arches is proposed and studied in this paper.Based on full-scale mechanical test system of arch,research is made on the failure mechanism and mechanical properties of CC arch.Then,a mechanical calculation model of circular section is established for the arches with arbitrary section and unequal rigidity;a calculation formula is deduced for the internal force of the arch;an analysis is made on the influence of different factors on the internal force of the arch;and a calculation formula is got for the bearing capacity of CC arch through the strength criterion of bearing capacity.With numerical calculation and laboratory experiment,the ultimate bearing capacity and internal force distribution is analyzed for CC arches.The research results show that:1)CC arch is 2.31 times higher in strength than the U-shaped steel arch and has better stability;2)The key damage position of the arch is the two sides;3)Theoretical analysis,numerical calculation and laboratory experiment have good consistency in the internal force distribution,bearing capacity,and deformation and failure modes of the arch.All of that verifies the correctness of the theoretical calculation.Based on the above results,a field experiment is carried out in Liangjia Mine.Compared with the U-shaped steel arch support,CC arch support is more effective in surrounding rock deformation control.The research results can provide a basis for the design of CC arch support in underground engineering.

乳化沥青与泡沫沥青冷再生技术发展综述

针对乳化沥青与泡沫沥青冷再生技术发展过程中的关键问题,介绍了冷再生技术的发展现状,分析了乳化沥青与泡沫沥青混合料的材料组分性能,总结了冷再生沥青混合料配合比设计方法和路面结构设计方法,论述了相关路用性能演化规律以及施工工艺和施工设备,提出了冷再生技术的未来发展趋势。研究结果表明:冷再生沥青混合料的材料组成成分间相互作用机制及强度破坏机理复杂,回收沥青混合料来源和掺量以及沥青老化程度、沥青以及外加剂种类及含量均会显著影响冷再生沥青混合料的材料性能;不同的冷再生沥青混合料设计方法在级配选择、沥青等级、成形方法、养护方式以及性能评价指标等方面差别较大,大多采用试验测试法指导配合比设计;冷再生沥青路面设计方法经历了从经验法到力学-经验法的转变,通常将冷再生材料视为无黏结颗粒材料或者沥青黏结材料进行结构设计,目前仍缺乏符合冷再生沥青混合料材料特性的力学失效设计准则;在工程应用方面,应充分考虑冷再生结构层位及力学响应,明确抗车辙、抗水损害、抗疲劳和低温抗开裂的性能需求,以指导冷再生沥青混合料的材料组成设计;未来应从施工工艺和材料组成两方面加强冷再生沥青混合料性能优化研究,建立以力学指标为基础的养生时间评估体系,完善适用于中国气候条件的冷再生结构层施工规范,加强现场试验的数据检测和收集工作,实现对冷再生沥青路面结构设计方程的有效标定。

基于精细化DEM建模的冷再生混合料断裂性能分析

冷再生沥青混合料包含水泥、乳化沥青、旧料等成分,具有材料组成复杂、界面结构多变的特点,其对冷再生混合料的抗裂性能具有显着影响。以冷再生沥青混合料的断裂性能为研究对象,提出一种精细化的数值建模方法,该方法包括细观结构特征精细重构和力学参数精确获取。采用彩色乳化沥青区分材料内部真实组成结构,并经过图像处理和MATLAB程序处理导入离散元(DEM)数值仿真软件中,进行冷再生混合料结构精细化重构;结合SEM原位力学测试方法获取考虑试件尺寸和加载速率影响的沥青砂浆精确力学参数,建立精细化的离散元数值仿真模型;基于精细化建模开展冷再生沥青混合料断裂性能和关键失效机理分析,并通过室内试验进行验证。数值仿真和室内试验结果表明:基于细观结构精细化重构和材料参数精确获取的离散元建模方法可以有效模拟分析冷再生沥青混合料的断裂性能;冷再生混合料的整体断裂特性属于脆性断裂,抗拉强度低的冷再生沥青砂浆是混合料内部的薄弱区域,混合料内部主要断裂界面为冷再生沥青砂浆-骨料界面。提高沥青砂浆黏聚强度和材料内部界面强度可以显著改善冷再生沥青混合料的抗裂性能。