基于热、力荷载传递机理的能量桩鲁棒性设计原理

Energy piles are a new sustainable technology for civil engineering. They extract geothermal energy from the ground subsurface to meet the cooling and heating needs of buildings, and provide clean energy. The energy piles can be developed from traditional bored piles through installing the geothermal loops in the pile structural elements. Hence this new technology for efficiently reducing carbon emission does not require too much additional construction cost. However, due to the uncertainty in temperature change, soils, design models and mechanical loads, the current geotechnical design of energy piles is realized with empirical approaches. The factor of safety used for energy piles is at least twice of those used for traditional piles, which leads to considerable additional cost. To this end, this research aims at investigating the thermal-mechanical load-transfer mechanism for energy piles under uncertain environment through (1) developing a three-dimensional geotechnical design model for energy piles based on finite difference method, (2) conducting soil laboratory and field tests and implementing the temperature-dependent soil parameters into the energy pile model, (3) calibrating model and parameter uncertainty using Bayesian approach based on field test data, and (4) quantifying the various uncertain factors on the bearing capacity and performance of energy piles. This research will propose a robust geotechnical design approach that can meet the strength, performance and cost requirements for energy piles. The robust design approach can minimize the influence of uncertain factors on the geotechnical design. The outcomes of this proposed research will enhance the applications of this green building technology to achieve the energy efficiency and the carbon emission reduction for the civil engineering industry in China.

能量桩是一种利用地热来给城市建筑提供制热和制冷的可持续土木工程技术，有助于减少碳排放。该方法在传统的钻孔灌注桩内预埋管状换热器，额外的建造费用少，因而是一种经济高效节能的减排技术。然而由于温度变化、土体参数的变异性、模型误差、外部荷载等众多不确定因素的影响，目前的能量桩岩土设计普遍采用经验法，其安全系数是传统桩的2至3倍，带来严重浪费。本课题通过研发基于有限差分方法的能量桩三维岩土模型，开展试验研究土体参数受温度变化影响的规律，并采用贝叶斯方法利用现场实测数据校核模型误差和参数误差，精确量化各种不确定因素对承载力和服役性能的影响，得到不确定环境下温度循环和力学荷载共同作用下的桩土荷载传递规律，提出能同时满足强度、服役性能和造价等多个目标的能量桩鲁棒性设计方法，将不确定性因素对其岩土设计的影响降到最低。本课题的研究成果将推广这一绿色建筑技术，和进一步促进我国土木工程建设中的经济高效节能减排。

本项目研发了能量桩的岩土设计的鲁棒方法。能量桩是一种利用地热来给城市建筑提供制热和制冷的可持续土木工程技术，有助于减少碳排放。然而由于温度变化、土体参数的变异性、模型误差、外部荷载等众多不确定因素的影响，之前的能量桩岩土设计普遍采用经验法，其安全系数是传统桩的2至3倍，带来严重浪费。本项目研发了基于有限差分方法的能量桩岩土设计模型（包括理论公式和代码），并使用贝叶斯方法利用现场实测数据校核模型误差和参数误差。基于研发的能量桩可靠度模型，精确量化了各种不确定因素对能量桩承载力和服役性能的影响，得到了不确定环境下温度循环和力学荷载共同作用下的桩土荷载传递规律。本项目在国际上首次提出并完成了可以量化和控制各种不确定因素对能量桩岩土设计的影响的能量桩岩土模型，包括能量桩的首个（1）能量桩的随机场模型、（2）能量桩的鲁棒模型和（3）全周期设计模型。 以上三个独立又相互关联模型已经发表在国际著名SCI期刊和国际会议上，可以为后续的理论研究、工程应用，国产工业设计软件的研发提供基础。