Characterizing void ratio and compressibility of Holocene peat with CPT for assessing coastal–deltaic subsidence

Abstract

Cone penetration testing (CPT) was used to determine the void ratio and compressibility of Holocene peat present in the coastal-deltaic plain of the Netherlands, to explore its application for mapping the subsidence potential of this low-lying area. CPT sounds the mechanical behaviour of subsurface layers when penetrated with a cone, and is the most widely used site investigation method in the Netherlands. In this study 41 peat layers in the coastal-deltaic plain were sounded, and subsequently cored for determination of peat type, organic matter content, degree of decomposition and void ratio. The results revealed that cone resistance depends on the void ratio of the peat layer. The compression parameters coefficient of volume compressibility (m v ) and compression index (C c ) were derived from this. The results further revealed that the compressibility of the peat increases with increasing organic matter content. It is concluded that for mapping the susceptibility of the coastal-deltaic plain to future subsidence by peat compression, CPT has the potential to become a useful tool, as thousands of CPTs are conducted in the Netherlands each year, and their logged measurements are stored in a freely accessible national database.

Disentangling and Parameterizing Shallow Sources of Subsidence: Application to a Reclaimed Coastal Area, Flevoland, the Netherlands

“…During both coring campaigns, the sediments encountered in the cored boreholes were classified into four different lithologies: sand, clay, organic clay, and peat. For the bulk density and porosity of these lithological classes, typical values of sand and clay encountered in Flevoland (De Glopper, ) and peat in the Netherlands were used (Koster, De Lange, et al, ; Table ). Areas with the thickest coastal sequence (4–10 m), that is, the western part of the study area, experienced most subsidence.…”

Peat layer accumulation and post‐burial deformation during the mid‐late Holocene in the Po coastal plain (Northern Italy)

“…Recently formed peat has a very loose structure, high void ratio and consequently high compressibility (van Asselen & Roosendaal, ; Hobbs, ; Koster, Lange, Harting, Heer, & Middelkoop, ; Lefebvre, Langlois, Lupien, & Lavallee, ; Price & Schlotzhauer, ). On the other hand, peats covered by several metres‐thick sediment packages are subject to post‐burial consolidation, through expulsion of pore water and rearrangement of their internal sedimentary structure (van Asselen et al, ).…”

“…Additionally, sedimentological features, such as palaeosols, can be detected within lithologically homogeneous floodplain successions (Amorosi, Bruno, Cleveland et al, 2017). Recently, Koster et al (2016), Koster, Lange et al (2018) proposed a method to estimate the amount of peat compaction based on CPT measurement.…”

Human-caused avulsion in the Rhine-Meuse delta before historic embankment (The Netherlands)

“…We correlated these events to human activity using archaeological artifacts that were found on the natural levees and on top of the peat. Peatland-surface elevation before avulsion was reconstructed for each 14 C sampled site (including compaction correction- Koster et al, 2016Koster et al, , 2018; see the Data Repository) to assess the gradient advantage along the new course through the pristine peatlands over the abandoned course.…”