Test data underlying the PhD thesis: Characterization of the mechanical properties of wooden foundation piles (G. Pagella) - TU DELFT

An extensive experimental campaign was conducted in this PhD research to characterize the mechanical properties along: 70 “new” full-size saturated spruce (<em>Picea abies</em>) and pine (<em>Pinus sylvestris</em>) foundation piles; 60 historical full-size saturated spruce (Picea abies) and fir (Abies) piles retrieved from two bridges in the city of Amsterdam, 100-300 years old and with different levels of decay. The data were collected from the experimental test campaign on the wooden foundation piles extracted from the soil in Amsterdam. The following methodology is adopted for achieving the main goals:The mechanical properties along the full-size “new” piles are investigated through the execution of large-scale axial compression tests on pile segments, extracted from their head, middle-part and tip. Pile segments with different diameters are investigated (ranging from 130 mm to 280 mm), with the goal of investigating the variability of saturated compressive strength and stiffness along the pile. The relationships between the saturated compressive strength and parameters characterized with visual and machine grading were investigated. On this basis, possible strength classes for the characteristic compressive strength based on visually-graded parameters were determined for spruce and pine piles. The results provide a basis for the engineering design and assessment of timber foundation piles and they can be used together with the provisions given in the new standard (Eurocode 5 2023).The second objective of this work is the detailed characterization, in terms of material and mechanical properties, of the historical saturated piles, with specific reference to the influence of bacterial decay on their remaining saturated compressive strength. The historical piles have been exposed in the soil for approximately 100, 135 and 295 years. Thus, it is possible to assess the remaining compressive strength of the piles in relation to bacterial decay after three distinct periods of service time. Large-scale compressive tests on full-size segments extracted from head, middle-part and tip were conducted to study the effect of decay along the pile. Small-scale compression tests were carried out on samples retrieved from the pile’s cross section, to study the influence of decay radially within the pile. Several techniques are adopted for this characterisation: micro-drilling measurements, computer tomography (CT) scans, and light microscopy observations.The applicability of micro-drilling measurements is studied to assess the amount of decay in the historical piles, as an alternative to the current extraction of drill cores. Correlations between the material and mechanical properties of the samples and the micro-drilling signals are investigated, to check the reliability of micro-drilling in identifying decay both from a qualitative and quantitative point of view. Based on a large database of micro-drilling signals collected from every historical pile segment, an algorithm is developed to determine the amount of decay within the pile at the position of the measurement.Two prediction models are presented: one for the saturated compressive strength of “new” spruce and pine piles, based on machine grading of their dynamic modulus of elasticity, measurable in practice with frequency response measurements. One for the direct prediction of the remaining saturated compressive strength along in-situ historical timber piles, based on the remaining sound cross-sectional area determined with underwater micro-drilling performed on the pile head.The novelty of this research lies in the characterization of the mechanical properties along the length of saturated spruce and pine piles, providing reliable saturated compressive strength values and grading specifications which enable engineers to adequately design timber foundation piles. These values can be used together with the provisions in the new Eurocode 5 2023. An innovative application of micro-drilling measurements is introduced, for the in-situ assessment of historical timber foundation piles and estimation of their remaining short-term compressive strength. This serves as basis for engineering retrofitting of timber foundations currently in use under historic buildings and strategical structures such bridges and quay walls in the city of Amsterdam. The micro-drilling approach contributes to the research framework in the city of Amsterdam, supporting testing and modelling methods for estimating decay, (residual) load-carrying capacity, and remaining service life models of timber pile foundations. This knowledge has broader applicability and potential extension to de delta cities across European countries, such as Stockholm (SE), Hamburg (DE) and Venice (IT), but also overseas locations including Boston (US).

本博士研究开展了大规模试验项目，以表征两类全尺寸饱和原木桩基的沿程力学性能：其一为70根“全新”全尺寸饱和云杉（*Picea abies*）与欧洲赤松（*Pinus sylvestris*）桩基；其二为60根历史全尺寸饱和云杉（*Picea abies*）与冷杉（*Abies*）桩基，这些桩基取自阿姆斯特丹两座桥梁，桩龄为100至300年，且腐朽程度各不相同。
本次试验数据采集自阿姆斯特丹出土木质桩基的相关试验项目。
为达成核心研究目标，本研究采用如下试验方法：
针对全新全尺寸桩基，本研究通过对从桩头、桩身中段及桩尖截取的桩段开展大型轴向压缩试验，表征其沿程力学性能。试验涵盖直径范围130 mm至280 mm的不同规格桩段，旨在探究饱和抗压强度与刚度沿桩身的变异性。研究同时分析了饱和抗压强度与视觉分级、机械分级所得参数间的关联，并据此确定了基于视觉分级参数的云杉与松木桩基抗压强度标准值对应的强度等级。本研究结果可为木质桩基的工程设计与性能评估提供依据，且可与新版标准《欧洲规范5（2023）》（Eurocode 5 2023）中的相关条款结合使用。
本研究的第二项核心目标是从材料与力学性能维度，对历史饱和桩基开展精细化表征，重点探究细菌腐朽对其剩余饱和抗压强度的影响。本次研究涉及的历史桩基在土壤中埋藏时长分别约为100年、135年与295年，据此可评估三类不同服役时长的桩基在受细菌腐朽后的剩余抗压强度。研究人员对从桩头、桩身中段及桩尖截取的全尺寸桩段开展大型压缩试验，以分析腐朽沿桩身的分布规律；同时对从桩横截面截取的试样开展小型压缩试验，以探究腐朽沿桩径向的分布特征。本次表征工作采用了多项技术手段：微型钻孔测试、计算机断层扫描（CT）以及光学显微观测。
本研究探究了微型钻孔测试用于评估历史桩基腐朽程度的适用性，以替代当前主流的钻芯取样方法。研究分析了试样的材料与力学性能同微型钻孔信号间的关联，以从定性与定量两个维度验证微型钻孔技术识别腐朽的可靠性。基于从所有历史桩段采集得到的大型微型钻孔信号数据库，本研究开发了一种算法，可用于确定测量位置处桩身内部的腐朽程度。
本研究提出了两类预测模型：其一基于动态弹性模量的机械分级参数（可通过频率响应测试在实际场景中获取），用于预测全新云杉与松木桩基的饱和抗压强度；其二基于通过桩头水下微型钻孔测试确定的完好剩余横截面积，用于直接预测原位历史木质桩基的沿程剩余饱和抗压强度。
本研究的创新之处在于首次对饱和云杉与松木桩基的沿程力学性能开展系统表征，提供了可靠的饱和抗压强度参数与分级规范，可帮助工程师合理开展木质桩基的工程设计。相关参数可结合新版《欧洲规范5（2023）》（Eurocode 5 2023）中的条款使用。本研究还创新性地将微型钻孔测试应用于历史木质桩基的原位评估与剩余短期抗压强度预测，可为阿姆斯特丹市内历史建筑及桥梁、码头岸壁等战略结构下方在用木质基础的工程加固提供依据。微型钻孔测试方法丰富了阿姆斯特丹的研究框架，可为木质桩基的腐朽程度评估、（剩余）承载能力估算以及剩余服役寿命建模提供测试与建模方法支撑。该研究成果具备更广泛的应用前景，可推广至欧洲多国的三角洲城市，如斯德哥尔摩（SE）、汉堡（DE）与威尼斯（IT），同时也可应用于包括波士顿（US）在内的海外地区。