A laboratory characterisation of the response of intact chalk to cyclic loading

Ahmadi-Naghadeh, Reza; Liu, Tingfa; Vinck, Ken; Jardine, Richard J.; Kontoe, Stavroula; Byrne, Byron W.; McAdam, Ross A.

doi:10.1680/jgeot.21.00198

Cited by 11 publications

(5 citation statements)

References 25 publications

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“…Such a result is in contrast to what has been observed for other materials (e.g. [3]), for which a larger amplitude A causes a faster degradation. Viscous effects might explain the observed behaviour.…”

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confidence: 99%

Experimental investigation of the effects of fatigue on caprock materials in H2 storage projects

Ciancimino,

Maria Cosentini,

Foti

et al. 2023

SEG

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The intermittent nature of renewable energy sources unavoidably limits their application as primary power supplies. In this sense, balancing the production/demand cycles over seasonal and annual timescales is essential for decarbonizing our economy. An effective long-term solution is represented by hydrogen underground storage in depleted hydrocarbon fields [1]. During overproduction periods, extra power is stored in the form of hydrogen in a porous reservoir formation, surrounded by a low-permeability caprock. Ensuring the integrity and the sealing efficiency of such material over the fatigue loading induced by storage/withdrawal cycles is thus fundamental for preventing hydrogen from escaping into the surrounding formations. A substantial amount of research has been conducted in the past to define the impact of fatigue on the response of either hard or soft rocks (e.g. [2]). Nevertheless, very few studies focused on the cyclic behaviour of caprock-like materials, i.e. structured stiff clays subjected to large confining pressures. Those are characterized by the distinctive stress-strain behaviour of clays together with a significantly larger undisturbed shear strength. When subjected to cyclic loading, progressive destructuration takes place, leading to softening of the response and eventually to fragile failure. This research fits within this context, focusing on the development of an effective methodology to assess fatigue-related risks in H2 storage projects. To this end, a series of monotonic and cyclic triaxial tests were performed to investigate the influence of loading frequency f (or, equivalently, the period T = 1/f ), maximum deviator stress qmax and loading amplitude A on the response of the material. The latter is a stiff clay with silt (clay fraction, d < 2mm, is equal to 50% and the silt fraction, d < 60mm, is 49%) with an average carbonate content of 40%. The liquid limit is wL = 43% and the plastic limit is wP = 25%. Specimens were consolidated under K0 conditions to an effective stress state consistent with its lithostatic value (namely, q = 6.3MPa and p’ = 8.1MPa). Monotonic and cyclic shearing were applied through loading-compression paths under undrained conditions. A preliminary summary of the results of the cyclic tests is presented in Figure 1a, where the fatigue life Nf is plotted against the corresponding qmax. Only two tests (represented as triangles in the plot) were interrupted before failure, due to their excessive duration. Most of the tests were conducted employing A ≈ 5.3MPa, except for two tests imposing A = 3.25MPa. The tests were carried out either with T = 5min (f = 3.3∙10-3Hz) or T = 250min (f = 6.7∙10-5Hz). Consistently with previous findings (e.g. [2]), Nf decreases with increasing qmax. In particular, Nf seems to be well predicted by a linear regression (in logarithmic scale) when the tests are conducted at consistent A and f values. The influence of A is instead somehow counterintuitive as decreasing A implies a reduction of Nf. Such a result is in contrast to what has been observed for other materials (e.g. [3]), for which a larger amplitude A causes a faster degradation. Viscous effects might explain the observed behaviour. For a given qmax, adopting a smaller A implies oscillating around a larger mean deviator stress qmean. Assuming that the creep strain rate increases as the stress state approaches the limit state surface [e.g. 4], smaller A values would also imply summing larger creep strains to those induced by cyclic degradation. The dependency of the mechanical response on the strain-rate applied at shearing provides further evidence of the relevance of viscous effects. Figure 1b reports the comparison between two cyclic tests (A and B in Figure 1a) conducted applying the same stress history, but different f (and, thus, average ). The specimen sheared with a lower f (test A) presents a significantly larger accumulation of with increasing loading cycles Ncyc, leading to failure after few cycles. Conversely, slower destructuration takes place in test B, which requires a larger number of cycles to fail. Figure 1c-d compare the cyclic stress-strain responses observed for tests A and B with the monotonic curves obtained employing strain-rates which are consistent with the equivalent average ones implicitly adopted in the cyclic tests ( equal to 0.01%/min and 0.5%/min). The cyclic response observed in test A is well-enveloped by the monotonic curve obtained for = 0.01%/min. Destructuration takes place with cyclic loading, inducing progressive softening of the material response, so that, during the 7th cycle, the strength reduces below qmax, leading to sudden failure. Conversely, about 60 cycles are needed in test B before approaching the monotonic resistance characteristic of = 0.5%/min. The relevance of the strain rate on the material response suggests that laboratory tests should be used with care for boundary value problems having very low loading frequencies, such as hydrogen storage. As those frequencies are not compatible with feasible experimental times, a viable testing procedure might require monotonic and cyclic tests at different strain rates. The cyclic tests shall be done at frequencies larger than the field ones. The monotonic tests shall instead be run at both the strain-rate of the field and the one of the cyclic tests. This would allow rescaling the cyclic response of laboratory tests to the one of the field frequency.

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confidence: 99%

Experimental investigation of the effects of fatigue on caprock materials in H2 storage projects

Ciancimino,

Maria Cosentini,

Foti

et al. 2023

SEG

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“…The surrounding intact chalk provides stiff radial containment to the reconsolidated putty annuli formed around the pile shafts and constrains any dilation that develops as the putty fails monotonically or degrades under cycling. Ahmadi-Naghadeh et al (2022) investigated intact SNW chalk's undrained cyclic triaxial behaviour under in-situ stress conditions. High quality samples could withstand one-way deviator stress amplitudes, q cyc = Δσ 1 -Δσ 3 , up to 700 kPa in a fully stable manner.…”

Section: Monotonic and Cyclic Behaviour Of Snw Chalkmentioning

confidence: 99%

Axial cyclic loading of piles in low-to-medium-density chalk

et al. 2024

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Comprehensive field investigations into the axial cyclic loading behaviour of open-steel pipe piles driven and aged in low-to-medium density chalk identify the conditions under which behaviour is stable, unstable or metastable. Post-cycling monotonic tests confirmed that stable cycling enhanced pile capacity marginally, while unstable cases suffered potentially large losses of shaft capacity. Metastable conditions led to intermediate outcomes. The patterns by which axial deflections grew under cyclic loading varied systematically with the normalised loading parameters and could be captured by simple fitting expressions. Cyclic stiffnesses also varied with loading conditions, with the highest operational shear stiffnesses falling far below the in-situ seismic test values. The monotonic and cyclic axial responses of the test piles were controlled by the behaviour of, and conditions within, the reconsolidated, de-structured, chalk putty annuli formed around pile shafts during driving. Fibre-optic strain gauges identified progressive failure from the pile tip upwards. Large factors of safety were required for piles to survive repetitive loading under high-level, two-way, conditions involving low mean loads, while low amplitude one-way cycling had little impact. A simple ‘global’ prediction procedure employing interface shear and cyclic triaxial tests is shown to provide broadly representative predictions for field behaviour.

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“…Cyclic loading was central to ALPACA. More than 20 locally instrumented cyclic triaxial tests were conducted on intact chalk specimens, which demonstrated a response more like that of crystalline rocks or metals than sedimentary soils (Ahmadi-Naghadeh et al, 2022). Noting that the near shaft, fully de-structured chalk, dominates axial capacity development in chalk, Liu et al (2022) conducted suites of locally instrumented monotonic and cyclic triaxial tests on chalk that had been de-structured by dynamic compaction at natural water content before re-consolidation to the conditions applying adjacent to the pile shafts.…”

Section: Snw Test Site Conditions and Chalk Characterization Studiesmentioning

confidence: 99%

“…describe also the monotonic and cyclic tests performed on the larger ALPACA Plus piles.10Dissemination of resultsThe ALPACA and ALPACA JIP results are being disseminated through a coordinated series of open access journal papers byAhmadi-Naghadeh et al (2022),Buckley et al (2020a), (2023),Jardine et al (2023),Liu et al (2022 andVinck et al (2023) and articles in international conferences, including OSIG-2023. Parallel studies at another chalk site are reported byVinck et al (2023);Pedone et al (2023) andWen et al (2023a, b) report on related advances in numerical analysis.…”

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confidence: 99%

Driven pile behaviour in low-to-medium density chalk: the ALPACA JIP outcomes

Jardine,

Liu,

Kontoe

et al.

9th International SUT Offshore Site Investigation Geotechnics Conference Proceedings “Innovative Geotechnologies for Energy Tra

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A laboratory characterisation of the response of intact chalk to cyclic loading

Cited by 11 publications

References 25 publications

Experimental investigation of the effects of fatigue on caprock materials in H2 storage projects

Experimental investigation of the effects of fatigue on caprock materials in H2 storage projects

Axial cyclic loading of piles in low-to-medium-density chalk

Driven pile behaviour in low-to-medium density chalk: the ALPACA JIP outcomes

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