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Geotechnical Investigations of Wind Turbine Foundations Using Multichannel Analysis of Surface Waves (MASW)

机译：利用表面波多通道分析（MASW）的风力涡轮机基础的岩土工程研究

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The geophysical technique known as Multichannel Analysis of Surface Waves, or MASW (Park et al., 1999) is a relatively new seismic characterisation method which utilises Rayleigh waves propagation. With MASW, the frequency dependent, planar travelling Rayleigh waves are created by a seismic source and then measured by an array of geophone receivers. The recorded data is used to image characteristics of the subsurface.This thesis explains how MASW was used as a geotechnical investigation tool on windfarms in the lower North Island, New Zealand, to determine the stiffness of the subsurface at each wind turbine site. Shear‐wave velocity (VS) profiles at each site were determined through the processing of the MASW data, which were then used to determine physical properties of the underlying, weathered greywacke.The primary research site, the Te Rere Hau Windfarm in the Tararua Ranges of the North Island, is situated within the Esk Head Belt of Torlesse greywacke (Lee & Begg, 2002). Due to the high level of tectonic activity in the area, along with the high rates of weathering, the greywacke material onsite is highly fractured and weathering grades vary significantly, both vertically and laterally. MASW was performed to characterise the physical properties at each turbine site through the weathering profile. The final dataset included 1‐dimensional MASW shear‐wave evaluations from 100 turbine sites. In addition, Poisson’s ratio and density values were characterised through the weathering profile for the weathered greywacke. During the geotechnical foundation design at the Te Rere Hau Windfarm site, a method of converting shear wave velocity profiles was utilised. MASW surveying was used to determine VS profiles with depth, which were converted to elastic modulus profiles, with the input parameters of Poisson’s ratio and density.This study focuses on refining and improving the current method used for calculating elastic modulus values from shear‐wave velocities, primarily by improving the accuracy of the input parameters used in the calculation.Through the analysis of both geotechnical and geophysical data, the significant influence of overburden pressure, or depth, on the shear wave velocity was identified. Through each of the weathering grades, there was a non‐linear increase in shear wave velocity with depth. This highlights the need for overburden pressure conditions to be considered before assigning characteristic shear wave velocity values to different lithologies.Further to the dataset analysis of geotechnical and geophysical information, a multiple variant non‐linear regression analysis was performed on the three variables of shear wave velocity, depth and weathering grade. This produced a predictive equation for determining shear wavevelocity within the Esk Head belt ‘greywacke’ when depth and weathering data are known. If the insitu geological conditions are not comparable to that of the windfarm sites in this study, a set of guidelines have been developed, detailing the most efficient and cost effective method ofusing MASW surveying to calculate the elastic modulus through the depth profile of aninvestigation site.
机译：被称为表面波多通道分析或MASW的地球物理技术（Park等，1999）是一种相对较新的利用瑞利波传播的地震表征方法。使用MASW，由地震源产生频率相关的平面行进瑞利波，然后由地震检波器阵列进行测量。记录的数据用于对地下特征进行成像。本文说明了如何将MASW用作新西兰北岛下部风电场的岩土工程勘察工具，以确定每个风力涡轮机站点的地下刚度。通过处理MASW数据确定每个站点的剪切波速（VS）剖面，然后将其用于确定基础的风化灰w的物理性质。主要研究站点是Tararua山脉的Te Rere Hau Windfarm北岛的岛屿位于Torlesse greywacke的Esk头带内（Lee＆Begg，2002）。由于该地区的构造活动水平很高，而且风化率很高，因此现场的格瑞瓦克材料高度断裂，风化等级在垂直和横向上都有很大变化。进行MASW以通过风化剖面表征每个涡轮机位置的物理特性。最终数据集包括来自100个涡轮机站点的一维MASW剪切波评估。此外，泊松比和密度值还可以通过风化的格里瓦克的风化曲线来表征。在Te Rere Hau Windfarm站点的岩土基础设计过程中，采用了一种转换横波速度剖面的方法。 MASW测量用于确定具有深度的VS剖面，并使用泊松比和密度的输入参数将其转换为弹性模量剖面。本研究着重于改进和改进用于从剪切波速度计算弹性模量值的当前方法通过对岩土和地球物理数据的分析，确定了上覆压力或深度对剪切波速度的重大影响。在每个耐候等级中，剪切波速度随深度呈非线性增加。这就突出了在为不同岩性分配特征剪力波速度值之前需要考虑上覆压力的条件。在岩土和地球物理信息的数据集分析中，对剪力波的三个变量进行了多变量非线性回归分析。速度，深度和风化等级。当已知深度和风化数据时，这产生了一个预测方程式，用于确定Esk Head带“ greywacke”内的剪切波速。如果本研究中的原位地质条件与风电场的地质条件不相符，则已制定了一套指南，其中详细介绍了使用MASW勘测通过调查地点的深度剖面计算弹性模量的最有效和最具成本效益的方法。

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    Hicks Malcolm Andrew;

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  • 年度 2011
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