Peat Layers Research Articles

Synsedimentary Compaction of Peat Under the Load of Alluvial System Sediments in the Most Basin (Czech Republic, Lower Miocene): From Weak Compaction to Strong Local Deformation of Clastics and Peat

Alluvial systems affected by peat layer compaction of a variable degree are studied all over the world, especially in areas of large river deltas and coastal plains. Ordinarily studied Holocene peat accumulations do not reach thicknesses of more than 6–10 m. This paper documents four ancient alluvial systems affected by peat compaction during the Lower Miocene in large exposures of open-cast lignite mines within the Most Basin, Czech Republic. Field observations and the study of 3000 borehole sections showed a clear dependence of the thickness and composition of the underlying peat on the scale of the accommodation space for loading by younger alluvial sediments. If the underlying partly compacted peat was tens to hundreds of meters in thickness, significant deformations of the peat appeared during its loading, leading up to the formation of growth faults. In such cases, missing parts of the coal seams were also observed below the alluvial systems. Especially borehole data showed that a linear correlation exists between the thickness of the alluvial sediments and the maximum instantaneous available compaction capacity of the underlying peat.

Revisiting past savanna environments: Pollen analysis of the Colbyn wetland on the southern African central plateau

A high-resolution, radiocarbon dated, pollen sequence of the ecotone between the Grassland and Savanna Biomes, was extracted from a 2.5 m peat core at the Colbyn wetland in South Africa. The lithology indicates transitions between organic sediment, clay, and well-preserved peat layers. The pollen and micro-charcoal records suggest interactions between the seasonal climate, burning and possible human and other disturbance. The vegetation development over the last 4000 cal yr BP is compared with chronologically parallel pollen sequences from the nearby Moreleta River and Rietvlei Dam sequences. The study, that can be correlated with wider regional isotopic records of the region, shows drier conditions c. 3800 to 3400 cal yr BP, and around 800 cal yr BP, and a wetter phase at Colbyn c. 3000–1500 cal yr BP.

Current Assessment of the Wetland Carbon Pool in Different Constituent Entities of the Russian Federation

A current more detailed assessment of the bog and wetland areas in the Russian Federation (RF) and the carbon stock in their peat layers has been conducted. Compared to the previous assessment (Vompersky et al., 1994), the creation of the geoinformation system (GIS) “Bogs of Russia” at the Institute of Forestry Science of the Russian Academy of Sciences (Vompersky et al. 2005), allowed to include, in addition to the cartographic basis, replenishable layers of thematic content and to determine the areas of peatlands and carbon stock in their peat layers not only for the whole country, but also for separate constituent entities of the Russian Federation country as a whole, but also for the constituent entities of the Russian Federation. It is important for the administration of each constituent territory to be aware of the peat reserve volumes in order for sustainable nature management to be maintained. It is shown that the area of bogs and marshlands amounted to 328 million hectares, peat stock — to 216.3 billion tons (abs. dry mass). The stock of carbon associated with the peat was 108.7 billion tons. Compared to previous estimates, the area decreased by 11% and carbon stock by 4%. The Annex to the article contains the data on the bogs and wetlands areas, overall carbon stock in their peat layers and specific carbon stocks per unit area of bogs and wetlands for different constituent entities of the Russian Federation. The carbon stocks estimates were also obtained separately for the main groups of bog and wetland habitat types.

Tropical peat composition may provide a negative feedback on fire occurrence and severity

Loss of peat through increased burning will have major impacts on the global carbon cycle. In a normal hydrological state, the risk of fire propagation is largely controlled by peat bulk density and moisture content. However, where humans have interfered with the moisture status of peat either via drainage, or indirectly via climate change, we hypothesise that its botanical composition will become important to flammability, such that peats from different latitudes might have different compositionally-driven susceptibility to ignition. We use pyrolysis combustion flow calorimetry to determine the temperature of maximum thermal decomposition (Tmax) of peats from different latitudes, and couple this to a botanical composition analysis. We find that tropical peat has higher Tmax than other regions, likely on account of its higher wood content which appears to convey a greater resistance to ignition. This resistance also increases with depth, which means that loss of surface peat in tropical regions may lead to a reduction in the subsequent ignitability of deeper peat layers as they are exposed, potentially resulting in a negative feedback on increased fire occurrence and severity.

Effects of fire on tree species composition and carbon stocks of a peat swamp forest in Central Kalimantan, Indonesia

ABSTRACT Peat swamp forests are important in the global carbon (C) budget because of the huge amount of C stored in these ecosystems, particularly in below-ground components. Indonesia has some of the greatest extent of peat swamp forests globally, yet many of them are being disturbed by fires that are becoming increasingly frequent. In Kalampangan, Central Kalimantan, the tree species (≥4.8 cm diameter) composition, aboveground biomass (AGB) and litter standing crop of peat swamp forests were sampled, and the overall ecosystem C stock estimated, within two 1-ha sampling plots, one of which was undisturbed (natural) and the other previously burned. The AGB and litter standing crop found in the natural forest totaled 341 and 6.77 Mg ha−1, respectively. The AGB declined more than six-fold to 53.2 Mg ha−1, and the litter standing crop declined by about half to 3.30 Mg ha−1 in the disturbed forest; the total number of tree species declined from 114 to 80 per hectare. The disturbed peat swamp lost just over 200 Mg C ha−1 to the atmosphere due to the combustion of tree biomass and the upper layer of the peat, but C stocks still remained very high overall (c. 1100 Mg ha−1) due to the thick layer of peat (>2 m) making peat swamp forest conservation imperative due to their huge carbon stocks.

Spatiotemporal variations of groundwater and gully impact in two peatland watersheds in the Upper Yellow River, Qinghai‐Tibet Plateau

AbstractThe spatiotemporal variability of groundwater level is an important property of peatland hydrology that directly alternates water storage. Nonetheless, the current understanding of the variations of groundwater level over long periods of time remains limited. In this study, we investigated two peatland watersheds (0.151 km2 for Watershed 1 and 0.844 km2 for Watershed 2) in the Zoige Basin in the upper watershed of the Yellow River to monitor temporal variability of groundwater level using self‐recorded water loggers over 4 years (2017–2021). The main results demonstrate that (1) groundwater level variations were controlled by gully drainage in sites adjacent to the gully but were more affected by rainfall in sites distant from the gully. The groundwater level near the gully downcut was lower than that near the gully without complete downcutting through the pear layer, with a maximum difference of 58.3 cm, indicating the longitudinal effect of groundwater level in the watershed. (2) Because the rainfall had a lag effect on the groundwater level, the length of lag gradually decreased with increased rainfall intensity (i.e., the lag time for sites distant from the gully was about 18 min shorter than that of sites close to the gully in Watershed 1). (3) The peak values of the groundwater level occurred simultaneously with the maximum and minimum rainfall in Watershed 2, and the peak occurrence time was related to the ratio of precipitation to evaporation. In the downstream sites, the groundwater level fluctuated more than the upstream ones in Watershed 2. Moreover, the average groundwater level in the upstream sites was 14.3 cm higher than that of the middle ones, indicating a decreasing trend of water storage along the gully. (4) The differences in groundwater level between wet and dry seasons were clear, but the difference was smaller in the upstream sites due to limited gully incision and higher water storage within the peat layer. Additionally, groundwater level changes were more extreme on rainy days during both the wet and dry seasons, but the different intensities of rainfall resulted in stable groundwater in the dry season and an oscillating groundwater level in the wet season in Watershed 2. This study uncovers the groundwater dynamics in the two peatland watersheds, which is of great significance for understanding runoff variation, ecohydrological processes, and wetland shrinkage.

The First Domesticated 'Cheongju Sorori Rice' Excavated in Korea.

Archaeological excavations led by Yung-jo Lee and Jong-yoon Woo were carried out twice at the Sorori paleolithic site, Cheongju, in the Republic of Korea, at the upper stream of the Geumgang river, the Miho riverside. A total of 127 rice seeds were excavated, including 18 ancient rice and 109 Quasi-rice, in 1998 and 2001. At the first excavation, eleven short japonica-type ancient rice and one slender smooth ancient rice with two kinds of Quasi-rice were excavated. The average length of the 11 short rice grains obtained from the first and second excavation was 7.19 mm and the average width was 3.08 mm, respectively. The Quasi-rice are apparently different from the rice and do not have bi-peak protuberances on their glume surface. At the second excavation, six short ancient rice chaffs and some Quasi-rice 2 were found. These short-grained ancient rice were comparable to the ancient rice that were excavated at the Illsan Neolithic site. Geologists and radiologists confirmed that the peat layer in which the rice found was older than 15,000 years. In this study, the morphological characteristics, crushing, and DNA band patterns related to the genetic polymorphism of rice grains in Cheongju Sorori were compared and analyzed for genetic similarities and differences with wild rice, weed rice, and modern rice. The morphological, ecological, and physiological variations in rice grains excavated from the Sorori site were presumed to denote the origin of rice domestication in Korea. It is also suggested that the results of the DNA sequencing of excavated rice are very important clues in estimating the origin of the early domestication of rice.

Effectiveness of the Sustainable Manure Pile Model for Ammonia Emission and Soil

In order to reduce odor emissions and surface water pollution while storing manure in field heaps near a barn, there is a challenge in properly designing manure-storage areas. Therefore, it is important to assess what solutions and conditions, considering environmental requirements, should be considered when storing manure in field heaps. The goal of the research is to determine the impact of various factors on the risk of nutrient leaching, soil, and gas emissions from solid manure heaps, considering climatic factors in the environment. Through various scientific studies, a manure pile model has been developed and evaluated for its impact on the risk of potential leaching and odor emissions (using hyperspectral gas emission analysis mass flow method) from manure and the dynamics of the 0–80 cm soil layer properties (nitrate (N-NO3) and nitrite (N-NO2), ammonia (NH3), mineral, and total N). Based on the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania. An optimal new manure heap model has been identified—a layer of not less than 20 cm of compacted straw (density 150–200 kg m−3) or a 10 cm layer of peat for absorbing manure slurries is formed on the soil surface, the manure heap is surrounded by an earth embankment not less than 30 cm high, the manure heap is covered with a layer of finely chopped straw not less than 10 cm thick, or 5 cm of sawdust, or 5 cm of peat. The manure is stored in the heap for 6–12 months. Following the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania, applicable to the northern part of the temperate climate zone and applying similar requirements to the relevant countries.

Determining peat's vertical hydraulic diffusivity and hydraulic conductivity from naturally occurring hydraulic pressure fluctuations measured at various depths

AbstractThis study presents a method that could be used to assess the in‐situ saturated vertical hydraulic conductivity of deeper and more decomposed peat layers. Deeper peat layers may exhibit very low permeability comparable to clayey sediments, where measurements and sediment sample collection are very difficult. More traditional measurement methods, such as slug‐tests and permeameter tests, have proven difficult to carry out in these conditions, necessitating an alternative method. For surpassing these possible constraints, this paper introduces a field method to quantify vertical hydraulic diffusivity, capitalizing on naturally occurring hydraulic pressure fluctuations measured with buried pressure sensors. The determined diffusivity values are used to calculate vertical hydraulic conductivity of peat using separately measured compressibility and specific storage values. Our research demonstrates the feasibility of using this method to evaluate vertical hydraulic diffusivity in lower peat layers. Calculated diffusivity values, combined with peat compressibility measurements, yield reasonable estimates of vertical hydraulic conductivity for dense fen peat comparable with more widely used in‐situ and laboratory methods. It also shows potential for vertical hydraulic characteristics parametrization in the upper less decomposed and compacted peat layers; however, further research is needed to understand the method's limitations in such conditions. Our approach provides a potential method for measuring in‐situ vertical hydraulic properties of less accessible peat layers, often overlooked, while also providing a way to surpass the scale‐dependency constraints inherent in peatlands' heterogeneous structure. Such information is necessary when studying the hydraulic interactions between groundwater aquifers and peatlands.

A nature‐inclusive future with healthy soils? Mapping soil organic matter in 2050 in the Netherlands

AbstractNature‐inclusive scenarios of the future can help address numerous societal challenges related to soil health. As nature‐inclusive scenarios imply sustainable management of natural systems and resources, land use and soil health are assumed to be mutually beneficial in such scenarios. However, the interplay between nature‐inclusive land use scenarios and soil health has never been modelled using digital soil mapping. We predicted soil organic matter (SOM), an important indicator of soil health, in 2050, based on a recently developed nature‐inclusive scenario and machine learning in 3D space and time in the Netherlands. By deriving dynamic covariates related to land use and the occurrence of peat for 2050, we predicted SOM and its uncertainty in 2050 and assessed SOM changes between 2022 and 2050 from 0 to 2 m depth at 25 m resolution. We found little changes in the majority of mineral soils. However, SOM decreases of up to 5% were predicted in grasslands used for animal‐based production systems in 2022, which transitioned into croplands for plant‐based production systems by 2050. Although increases up to 25% SOM were predicted between 0 and 40 cm depth in rewetted peatlands, even larger decreases, on reclaimed land even surpassing 25% SOM, were predicted on non‐rewetted land in peat layers below 40 cm depth. There were several limitations to our approach, mostly due to predicting future trends based on historic data. Furthermore, nuanced nature‐inclusive practices, such as the adoption of agroecological farming methods, were too complex to incorporate in the model and would likely affect SOM spatial variability. Nonetheless, 3D‐mapping of SOM in 2050 created new insights and raised important questions related to soil health behind nature‐inclusive scenarios. Using machine learning explicit in 3D space and time to predict the impact of future scenarios on soil health is a useful tool for facilitating societal discussion, aiding policy making and promoting transformative change.

The Growth and Carbon Sink of Tundra Peat Patches in Arctic Alaska

AbstractRecent amplified climate warming in the Arctic has caused profound changes in terrestrial ecosystems, with the potential for strong feedback on climate change. Arctic tundra landscapes have developed patchy and thin organic soil (peat) layers at the surface that may continue to grow into mature peatlands and become a larger carbon sink under future warming. Here we use paleoecological analyses of multiple soil and peat cores collected from the North Slope of Alaska to document and understand the formation and development histories of tundra peat patches and permafrost peatlands. We find a consistent peat development sequence for peat patches, first from mineral soils to sedge peat during the Little Ice Age, and then to Sphagnum peat during the recent warming with high carbon accumulation rates. These findings suggest that climate cooling is likely critical for the initial peat buildup on tundra soils due to reduced decomposition, whereas climate warming triggers the regime shift into an increased abundance of Sphagnum mosses that are likely central to enhancing their carbon sink capacity. Additionally, peat patches become similar to permafrost peatlands in the vicinity in terms of ecosystem processes and carbon dynamics, and therefore may have developed the same ecohydrological feedback system to maintain their long‐term stability. This study implies that the potential future expansion of peat patches into peatlands may strongly alter the carbon balance of Arctic tundra, supporting the new United Nations Environment Programme's report that calls for incorporating widespread shallow peat into understanding the peatland–carbon–climate nexus.

Unveiling subsurface heterogeneity in porous aquifers: Insights from hydrogeophysics and derivative analysis

Groundwater is a crucial resource, particularly in urban areas where the need for alternative water sources is rising. Securing groundwater resources is paramount, requiring a concentrated effort to assess these resources and mitigate the increasing water shortages in urban regions. Despite its significance, the application of hydrogeophysics and derivative analysis in understanding aquifer dynamics is often overlooked and underused. Consequently, this study argues that neglecting the integration of hydrogeophysics dataset and derivative analysis in aquifer characterization leads to developing models that lack solution-oriented approaches, hindering effective groundwater management. This study aimed to enhance understanding of aquifer dynamics for solution-based modeling while emphasizing the importance of integrating hydrogeophysics dataset and derivative analysis to highlight aquifer system heterogeneities. The electrical resistivity tomography and derivative analysis of pumping test were used in this study to image the subsurface and amplify aquifer flow regimes respectively. The results of the electrical resistivity survey revealed a distinct layer of fine to medium-grain sand at depths of approximately 60 m in certain areas intercalated with medium-to-coarse-grain sand and thin layers of peat. Derivative analysis plots indicated that the predominant flow regime is linear and bilinear, with evidence of fracture dewatering during pumping cycles suggesting an unconfined aquifer. Additionally, aquifer heterogeneity and a no-flow boundary were evident during the pumping cycle. This study underscores the efficacy of combining hydrogeophysics and derivative analysis of pumping tests as a robust approach for imaging and validating subsurface conditions. The implications of these findings extend beyond the specific case study, offering valuable insights for groundwater utilization, monitoring, and management on a broader scale. By elucidating effective methodologies, this research enhances groundwater security and meets the escalating demand for sustainable water sources in urban areas. In conclusion, electrical resistivity tomography is an effective tool for characterizing subsurface aquifer systems, while derivative analysis of pumping tests is crucial for highlighting aquifer system heterogeneities. These methods offer a more practical interpretation compared to traditional drawdown versus time curve approaches, making the results invaluable for groundwater usage monitoring and management.

Aerobic and anaerobic decomposition rates in drained peatlands: Impact of botanical composition

Drained peatlands in temperate climates are under threat from climate change and human activities. The resulting decomposition of organic matter plays a major role in regulating the associated land subsidence rates, yet the determinants of aerobic and anaerobic peat decomposition rates are not fully understood. In this study, we sought to gain insight into the drivers of decomposition rates in botanically diverse peatlands (sedge, reed, wood, and moss dominant) under oxic and anoxic conditions. Peat samples were collected from the anoxic zone and incubated for 24 h (short) and 15 weeks (long) under either oxic or anoxic conditions. CO2 emissions, hydrolytic and oxidative exoenzyme potential activities, phenolic compound concentrations, and several edaphic factors were measured at the end of each incubation period.We found that 15 weeks of oxygen exposure of anoxic peat samples accelerated the average CO2 emissions by 3.9-fold. Reed and sedge peat respired more than wood and moss peat under anoxic conditions. Interestingly, CO2 emissions from anoxic peat layers under permanently anoxic conditions were substantial and given the thickness of peat deposits in the field, such activities may play an important role in long-term land subsidence rates and total CO2 emissions from drained peatlands. The results from the long-term incubations showed that decomposition rates appear to be also controlled by factors other than oxygen intrusion such as substrate availability. In summary, the botanical composition of the peat matrix, incubation conditions and time of incubation are all important factors that need to be considered when predicting peat decomposition and subsequent land subsidence rates.

Optimization design of cement mixing columns supported height embankment using Plaxis remote scripting and Gene-expression programming technique

This paper is going to present the advanced feature in Plaxis using remote scripting with Python wrapper. Python allows engineers to create Plaxis models, calculate construction phases, and plot the results automatically. The settlement estimation of a high embankment, supported by cement mixing columns (CMC), is presented as a case study. Approximately 500 models were created and analyzed within a few hours with different embankment heights, soft soil thickness, CMC spacing, and CMC diameter. This original database was used to develop a regression model using a Gene-expression programming (GEP) algorithm. The proposed GEP-based model with high accuracy could be applied to optimize the CMC design. In detail, the coefficient of correlation (R-value) of all phases is high and fluctuates from 0.967 to 0.976, while the mean absolute error of the model is lower than 0.009 m. The parametric study indicates that increasing the height of the fill embankment, the thickness of the peat layer, or the spacing between CMCs causes high settlement, while increasing the CMC diameter could significantly reduce the settlement of the embankment. The research results demonstrate that using Plaxis remote scripting and the GEP technique could help engineers run the numerical analysis much faster, leading to a more in-depth analysis to create better decision-making.

Modeling Geospatial Distribution of Peat Layer Thickness Using Machine Learning and Aerial Laser Scanning Data

Organic horizons including peat deposits are important terrestrial carbon pools, and various chemical, biological, and water exchange processes take place within them. Accurate information on the spatial distribution of organic soils and their properties is important for decision-making and land management. In this study, we present a machine learning approach for mapping the distribution of organic soils and determining the thickness of the peat layer using more than 24,000 peat layer thickness measurements obtained from field data, airborne laser scanning (ALS) data and various indices obtained from therein, as well as other cartographic materials. Our objectives encompassed two primary aims. Firstly, we endeavored to develop updated cartographic materials depicting the spatial distribution of peat layers. Secondly, we aimed to predict the depth of peat layers, thereby enhancing our understanding of soil organic carbon content. Continentality, a wet area map, latitude, a depth to water map with catchment area of 10 ha, and a digital elevation model were the most important covariates for the machine learning model. As a result, we obtained a map with three peat layer thickness classes, an overall classification accuracy of 0.88, and a kappa value of 0.74. This research contributes to a better understanding of organic soil dynamics and facilitates improved assessments of soil organic carbon stocks.

Utilization of Sand Cushion for Stabilization of Peat Layer Considering Dynamic Response of Compaction

Utilization of Sand Cushion for Stabilization of Peat Layer Considering Dynamic Response of Compaction

The applicability of scanner method to investigate rhizosphere in wetlands

Temporal changes in rhizosphere, including roots and rhizomes, are prerequisites for understanding plant community dynamics, while observation methods have room for development. Monitoring roots and rhizomes by non-destructive methods is desirable, particularly in wetlands, because plants often develop shallow roots that are determined by the water level. Here, we examined the applicability of flatbed scanner method, which allows for least destructive monitoring. The examination was performed on a post-mined peatland in Sarobetsu mire, northern Japan, where herbaceous plants are dominant. Photos (297 mm in height × 216 mm in width) were taken periodically using a scanner in transparent boxes installed in peat layers from 2020 to 2023. Most photos taken by the scanner showed clear for image analyses and were analyzed for temporal changes in root area and length of dominant species. Although root extraction was conducted automatically using open-source software, manual operations were required to increase root detectability and identification. The belowground plant organs were separated into main roots, fine roots, adventitious roots and rhizomes. The roots were mostly distributed within the photo planes, except for the deep rhizomes of Phragmites australis, indicating that this method captured most roots. In total, 62% of the roots were distributed above the groundwater level of which average was 7 cm below the peat surface. The examined species fluctuated in root area and length with upward trends and developed at different depths. We conclude that the scanner method proposed in this study is applicable to monitoring root dynamics, evaluated by the recruitment and growth at species level for the long term and provides a new insight into understanding rhizosphere dynamics in wetland ecosystems.

Conventional Sphagnum peatlite substrate can be reduced by 50% in stratified substrate systems while growing equivalent size and quality Pentas lanceolata

Floriculture crop production heavily relies on the use of peat-based substrates to quickly mass produce containerized crops. The sustainability of using peat moss has been an increasing concern for both horticultural stakeholders and the community. The concept of stratifying soilless substrates (i.e., vertically layering unique substrates atop of each other within the container) has been shown to reduce peat moss applications by upwards of 50 %. Although, most stratified substrate research has only studied an equal partition in which the substrate is evenly split into two layers. This necessitates further studying modification of the limits and optima for the depth of each layer. This study evaluated adjusting this stratified depth layer for possible further benefits, such as reduced water and peat moss applications. Lucky Star Dark Red Pentas lanceolata ‘PAS1231189’ was grown in one of four substrate treatments, including a (1) non-stratified 100 % peat and perlite blend (peat-lite), (2) 13.4 cm peat-lite placed above 4.4 cm pine bark (PB) horizon with the container consisting of 75 % (by vol.) peat-lite and 25 % (by vol.) PB; (3) 8.9 cm peat-lite placed above 8.9 cm PB layer with the container consisting of 50 % (by vol.) peatlite and 50 % (by vol.) PB; (4) 4.5 cm peat-lite placed above 13.3 cm PB with the container consisting of 25 % (by vol.) peat-lite and 75 % (by vol.) pine bark. Crops were placed on irrigation-actuated lysimetry systems to maintain substrate volumetric water contents between 0.20 and 0.30 cm3 cm−3. This study identified successful production of pentas in stratified profiles when the depth layer is ≥ 50 % peatlite by vol., with equal growth to pentas grown traditionally (i.e., 100 % peat-lite; non-stratified). Crops grown in a 25 % peat-lite : 75 % PB depth layer experienced significantly reduced growth with regards to growth index, quality, and dry biomass. Moreover, crops grown in the 25 % peat-lite by vol. also experienced faster peak inflorescence with a subsequent continuous decline in flower development due to water stress; whereas, plants grown in ≥ 50 % peatlite by vol. continued to develop blooms throughout the study. This study demonstrates that a popular floriculture crop can be grown by stratifying expensive floriculture media above inexpensive PB with little to no differences in growth if the stratified peat layer is equal or greater than 50 % the container vol.

A Case Study of Assessing the Accuracy of Secondary Consolidation Prediction Using Qualitative Approach

Infrastructure constructed, especially over soft organic soil layers, can be subjected to excessive settlement within its life cycle due to the complex behaviour of the soft soil with time. However, with necessary actions prior to construction, the impacts from such soil layers can be mitigated to some extent. The case under consideration is a leisure resort in Matara, a 15-storey hotel resting on a raft foundation near the southern coastal line of Sri Lanka. With time, some cracks have formed within the building, and an investigation was done to identify the cause for the crack formation. It has been determined that cracks have appeared due to the excessive settlement of the subsurface. Furthermore, ground investigation results suggest that a peat layer is beneath the building within a depth of 15-24m. As per the survey report on the settlement of the building, secondary consolidation of the soft soil significantly impacts the excessive settlement. Therefore, three methods were used to predict the secondary consolidation settlement of the peat layer beneath the building. The methods are prediction using empirical correlations, laboratory experiment results that will follow the constant coefficient of secondary consolidation throughout time and the qualitative method, which assumes that the secondary consolidation coefficient varies with time. Based on the above techniques, predictions were made, and results suggest that the qualitative method has a significant accuracy compared to the actual settlements of the building. These observations provide some proof that the coefficient of secondary consolidation varies with time according to the qualitative approach and does not remain constant throughout the lifespan of the building as suggested by conventional methods. KEYWORDS: Coefficient of secondary consolidation, Crack formation, Settlement, Soft soil, Time-dependent settlement

Sedimentary and stratigraphic architecture in the geoarchaeological context of Late-Holocene deposits in the eastern coastal plain of Belgium: Zwin region – Hoeke

A sedimentary investigation was carried out into the rise and fall of mediaeval Bruges’ maritime access. Because the mediaeval metropolis had no direct connection with the North Sea, its maritime connectivity during the High- and Late-Middle Ages depended on a tidal channel, known as the ‘Zwin’. In order to reconstruct the mediaeval physical environmental situation correctly, the entire Holocene sedimentary record was studied through undisturbed mechanically-drilled cores and electrical cone penetration tests (CPT-e). A detailed sedimentary analysis was complemented with radiocarbon dating and datable archaeological finds to resolve a timeframe for the sedimentary evolution. Tidal channel systems with diverse morphologic and sedimentologic characteristics prevail and cover a period from at least the Roman period till the Late-Middle Ages. The presence of a single peat layer directly on top of the Pleistocene substrate and the stratigraphic position of the tidal channel deposits relative to this peat layer, proves that no seawater entered this part of the Belgian coastal plain before the Late-Holocene. The tidal channel system that was active during the heydays of Bruges (the Zwin) was the last natural one. It silted up due to a further reduction of the accommodation space as a consequence of new embankments, possibly expedited by storms.