An Investigation of Two Peat Slope Failures in the Wicklow Mountains

For water content determinations on organic soils, several researchers have adopted lower oven-drying temperatures in the range 35−90°C (instead of the standardised range for mineral soils of 100-110°C) in order to prevent possible charring, oxidation and (or) vaporisation of substances other than water. However, at too low a temperature, not all of the relevant water is driven off. One major consequence of using such a wide range of drying temperatures for more sensitive materials is to produce considerable disparity in interpolated index values and in deduced correlations between water content and other engineering properties. This paper discusses the pros and cons regarding the ovendrying temperature adopted for routine water content determinations on organic sludges and residues. It concludes by recommending a standardised oven temperature of 105-110°C or 105 ± 5°C, a 24-h drying period and a suggested minimum wet specimen mass of 50 g.

Section: Oven-drying Temperaturementioning

confidence: 99%

Drying temperature and water content–strength correlations

O’Kelly¹

2014

“…The fibre content of the peat has been identified previously, at other locations, as a determining factor for the stability of Irish blanket peat (e.g. Boylan and Long 2010). The fibre content represents a direct botanical control on the properties and behaviour of the peat mass since the nature (sizes, forms, tensile strengths, shear strength against amorphous matrix, etc.)…”

Section: Botanical Compositionmentioning

confidence: 91%

Recent peat slide in Co. Antrim extends the known range of weak basal peat across Ireland

Dykes

2022

Peat instability and failure became an important topic of study following a series of damaging landslides in 2003. A peat slide in August 2014 at Croaghan, in the Orra Mountains of Co. Antrim, Northern Ireland, provided the first opportunity to directly compare estimates of peat shear strength from Direct Simple Shear (DSS) and tensile strength (TS) testing. Physical properties of peat from throughout the depth profile were obtained to provide reference characteristics for the strength test results, and to facilitate comparisons with results from locations where detailed botanical compositions have been analysed.Both methods showed that the basal peat at the study site had a shear strength much lower than 6 kPa. The physical properties are the same as at sites 150 km further southwest, so the composition of the peat at the study site is inferred to be dominated by sedges (particularly Eriophorum vaginatum) with some heathers (Ericacae) and mosses (including Sphagnum). The weak basal layer appears to be similarly lacking fibres, which allowed failure to occur in response to adverse water pressures arising from extreme rainfall. Basal shear strength of < 5 kPa is a reasonable starting assumption for planned engineering works on intact blanket peat in Ireland. Key wordsFabric/structure of soils, Landslides, Strength & testing of materials Notation F factor of safety Ksat saturated hydraulic conductivity p'c preconsolidation stress su undrained shear strength σ'v consolidation stress τh-max peak horizontal shear stress φ friction angle

“…Consequently, as summarised in the papers by O'Kelly (2014) and O'Kelly and Sivakumar (2014), there has been much debate regarding the appropriate t range for water content determinations of peat and other highly organic soils using the oven-drying method. Numerous researchers, including Boylan and Long (2010), Goodman and Lee (1962), Hosang and Locker (1971), Landva et al (1983), Marachi et al (1983) and Ng and Eischens (1983), have recommended using lower t values in the range 60-90°C for water content determinations of these soils, which is continued as routine practice to the present day in some commercial and research laboratories. However, as demonstrated experimentally for very different organic soils in the papers by O'Kelly (2004O'Kelly ( , 2005aO'Kelly ( , 2005bO'Kelly ( , 2005c and Skempton and Petley (1970), all of the relevant water is not fully evaporated from the test specimen at these lower t values, with the residual pore water interpreted as dry solids from the viewpoint of performing the water content calculations, thereby resulting in apparently lower values than the correct water content value (O'Kelly, 2004).…”

Section: Introductionmentioning

confidence: 99%

“…Hence, in summary, there are two bipolar views presented in the literature regarding the appropriate t range for water content determinations of peat and other organic soil materialsthat is, t values in the range 60-90°C (see the papers of Boylan and Long (2010), Goodman and Lee (1962), Hosang and Locker (1971), Landva et al (1983), Marachi et al (1983) and Ng and Eischens (1983), to name a few) or the standard t value of 105°C (O' Kelly, 2014;O'Kelly and Sivakumar, 2014;Skempton and Petley, 1970), although the latter studies mainly investigated soils from Ireland and England. For consistency, O'Kelly (2014), O'Kelly and Sivakumar (2014) and Skempton and Petley (1970) recommended that the values of water content corresponding to the t value of 105°C should be deduced and used in place of measured or reported water content values determined on the basis of lower t values, with methods presented in the papers by O'Kelly (2004O'Kelly ( , 2005a, O'Kelly and Li (2018) and Skempton and Petley (1970) for the purpose of performing these calculations.…”

Section: Introductionmentioning

confidence: 99%

Briefing: Water content determinations of peaty soils using the oven-drying method

O’KellyBrendan

FangKunbin

et al. 2022

In order to prevent possible charring, oxidation and (or) vaporisation of substances other than pore water, many researchers have adopted oven-drying temperature (t) values in the range 60–90°C for water content determinations of peat and other highly organic soils. This paper investigates the oven-drying characteristics of six very different highly decomposed peaty soils retrieved from south-west China for t values of 65, 85 and 105°C. Based on the presented experimental data, it is concluded that the standardised t value of 105°C used for testing of inorganic soil is also appropriate (and preferable to using lower t values) for routine water content determinations of these soils, which is in line with the growing consensus formed by other researchers on this topic. Further, the authors recommend a wet specimen mass of approximately 50 g and a 24 h oven-drying period in performing the oven-drying tests for t = 105°C. The paper also describes an existing approach to comparing and standardising water content values determined for the same organic soil, but on the basis of different t values, with the new data presented herein for the six Chinese soils used to strengthen its wider applicability in geotechnical engineering practice and related fields.