Effect of geomorphologocal setting on the erosion rates of sandstone in the coastal spray zone

弥生大桥是连接日本青岛和九州本岛的桥梁，由4个高3m、墙角70 °的四棱锥台砂岩块砌桥墩支撑。桥墩的四个侧壁分别大致面向东、南、西和北。由于风化和侵蚀，每个砂岩块体都有一个盘状凹陷。1992年和1994年分别对四个桥墩的所有墩块进行了沉降深度的测量，分别对应于大桥建成后的41年和43年。平均侵蚀深度以南向墙最大，西向墙和东向墙依次减小。这种侵蚀深度的差异主要是由于日照造成的。侵蚀深度与日照的关系可用线性函数表示。四个桥墩的回归线在图纸上是平行的。最高线为第四墩线，最低线为第一墩线。开发并建立了一种新的岩石表面水分原位无损监测技术。该方法和仪器对阐明盐风化的实际条件和机理是非常有用的.岩石表面水分变化的测量表明，岩石表面水分大波动的分布与深部凹陷的分布相吻合.用热示踪仪拍摄了桥墩的热红外图像。从这些图像中，我们可以获得有关盐风化的有用信息。

Yayoi Bridge, connecting Aoshima Island with Kyushu main island in Japan, is supported by four piers, which are masoned with sandstone blocks and are frustum of pyramid in shape, 3 m in height and 70ﾟ in wall angle. Four side walls of the piers face approximately east, south, west, and north, respectively. Each sandstone block has a dish-like depression due to weathering and erosion. The depth of the depression was measured for all blocks of the four piers in 1992 and 1994 corresponding to 41 and 43 years after the completion of the bridge respectively.The results of our research are summarized as follows.1. The average erosion depth is the largest on the south-facing wall, becomes gradually smaller on the west- and east-facing walls in this order. This difference in erosion depth acording to wall aspect mainly due to insolation. The relationship between erosion depth and insolation is expressed by linear function. The regression lines of four piers are parallel on graph paper. The uppermost line is a line of 4th pier and the lowest is of 1st pier.2. A new technique for nondestructive in situ rock-surface moisture monitoring was developed and established. This method and instruments are very useful to clarify the actual conditions and the mechanism of salt weathering.3. The measurement of rock-surface moisture change indicates that the distribution of large fluctuation in rock-surface moisture is coincident with the distribution of deep depression.4. Thermal infrared images of the piers were taken by themo-tracer. From the images, we can obtain useful informations on salt weathering.