The construction industry has been greatly developed in the past few decades, especially in the extensive use of underground space. The increasing amount of waste (e.g., soil, sludge, and rock) generated in the underground construction constitutes an important part of construction and demolition waste (CDW) but the related problems are rarely addressed in an independent quantitative study. In order to facilitate recycling of underground construction waste (UCW), quantitative methods for predicting UCW are proposed based on mass conservation in this study. Through on-site investigation and literature review, the source characteristics of UCW and corresponding recycling potential are firstly analyzed. Secondly, the corresponding quantitative mothed is proposed for predicting each type of UCW according to the principle of mass conservation. Finally, the proposed quantitative methods are applied in two real underground infrastructure projects to verify the accuracy. The results show that the accuracy of quantitative methods for predicting shield sludge and engineering soil is 82.03%-95.79% and 94.49% respectively. In addition, detailed geological and geotechnical analysis is the key to accurate management of waste generated in underground civil and infrastructure projects. In both cases, underground construction produced a large amount of construction waste with great recycling potential. UCW can theoretically reach 100% recycling, and full reuse and recycling of UCW will bring huge economic value and be conducive to the sustainable development of the construction industry.

The evaluation of the soil contaminated by heavy metals can help to judge whether the soil meets the standard and whether the pollution will threaten human health and the ecological environment. In this study, the farmland soil from eight districts in Beijing was used as the research object, and the concentration of heavy metal elements, Pb, As and Cd in the soils and agricultural products were analyzed. The analysis results showed that: (1) The evaluation based on the improved Hakanson method suggested that the crops exhibit a significantly higher ability to absorb Cd than to absorb Pb and As. Pb, As and Cd are all at normal level of ecological risk; among them, Cd is mainly in a moderate ecological risk, without strong ecological risk. (2) Based on the Improved analytic hierarchy process(AHP) of evaluation, 0.2317 is the average value of the integrated index of heavy metal pollution of soil in the study area, which is a mild level of pollution. (3) Through the calculation of various parameters in the Influence index of comprehensive quality(IICQ) of soil and agricultural products, it was found that 0＜IICQS＜1, suggesting that the environmental quality of soil is at a clean level. In summary, the pollution of heavy metals Pb, As and Cd in the farmland soils and crops in the eight districts of Beijing, including Fangshan, Daxing, Shunyi, and Shijingshan is at a low level, and no significant impact has been brought to the surrounding environment.