Stability Evaluation during Staged Construction

Ladd, Charles C.

doi:10.1061/(asce)0733-9410(1991)117:4(540)

Cited by 424 publications

(216 citation statements)

References 66 publications

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“…Furthermore, ðs u DSS =s 0 vc Þ NC is 0·46 for Booneschans fibrous peat and 0·47 for Uitdam sedge-reed peat (Zwanenburg and Jardine, 2015), with s u DSS =s 0 vc ¼ 0Á46 for Taylor River peat with w o = 500% (Foott and Ladd, 1981). These s u DSS =s 0 vc values are remarkably consistent and considerably greater than the range of 0·20-0·27 reported for NC clay or silt materials (Ladd, 1991). Other limited published s u DSS =s 0 vc data for Polish, Irish and Swedish peats (after Carlsten (2000), Farrell andHebib (1998), Farrell et al (1999) and Lechowicz (1994)) show much scatter in the range of 0·38-0·55.…”

Section: Geotechnical Research Volume 4 Issue Gr3supporting

confidence: 68%

“…Correlating with consolidation stress leads to normalised undrained strength ratio, s u TC =s 0 vc , values ranging 0·47-0·78 for conventionally sized triaxial specimens of fibrous peats (see Table 2), indicating that significant strength gains are achieved with consolidation, compared with the typical range of 0·30-0·35 for NC clay and silt materials (Ladd, 1991). (Ajlouni, 2000), with s u TC defined at the phase transformation point on the ESP trace described earlier, whereas ðs u fTC =s 0 vc Þ NC values of 0·62 for CK 0 UC (see Figure 11), 0·61 for CIUC and 0·59 (±22%) for CIUC (Zwanenburg and Jardine, 2015) were deduced based on estimated s u fTC values for Marken peat, Booneschans fibrous peat and Uitdam sedge-reed peat materials, respectively, where s 0 vc is the vertical consolidation stress at the start of the compression stage in the CU TC tests.…”

Section: Cu Tc Testingmentioning

confidence: 98%

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Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

O’Kelly

2017

Geotechnical Research

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Peat deposits are complex natural formations encountered in many geographical areas. Peat itself is considered as a challenging geomaterial, with many aspects of its behaviour seemingly remaining enigmas. This state-of-the-art review paper provides an extensive summary of current knowledge on the strength and shear behaviour of fibrous peats. Critical assessments and interpretations of the undrained strength, effective-stress strength and at-rest earth pressure coefficient parameter values determined for fibrous peat materials using standard and advanced laboratory apparatus are presented, focusing particularly on the consolidated undrained triaxial compression and direct simple shear approaches. Based on documented case histories of embankments, dikes and natural peat slopes, guidance is given for operational shear strength assessments in peat, aimed at bearing capacity and slope stability calculations, considering both the normalised undrained strength ratio and limit equilibrium effective-stress strength approaches. In particular, the botanical origin, structural anisotropy, humification level, likely initial overconsolidated state, tensile resistance associated with the peat fibres and possible scale effect related to the test-specimen size are discussed in the context of the strength mobilised for different testing apparatus. The test methodologies and interpretations of experimental results presented for fibrous peat in this paper should be transferable to other fibrous soil and soil-like materials. Notation

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Section: Geotechnical Research Volume 4 Issue Gr3supporting

confidence: 68%

Section: Cu Tc Testingmentioning

confidence: 98%

Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

O’Kelly

2017

Geotechnical Research

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“…(Ladd, 1991). For SS tests, s u-SS /σ' v values vary from 0.38 to 0.55, with one point lying outside this range.…”

Section: Laboratory Testingmentioning

confidence: 97%

Evaluation of peat strength for stability assessments

Boylan

Long

2014

Proceedings of the Institution of Civil Engineers - Geotechnica

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SynopsisIn this paper guidance is given for the assessment of peat strength for stability assessments based on laboratory undrained simple shear tests (SS). When considering the stability of peat, these tests will yield a conservative estimation of the in-situ strength of the peat mass. The study was motivated by recent interest in renewable energy developments in upland peat areas. The results of more than 111 SS tests from 16 sites in Ireland, Scotland and the Netherlands were studied. It was found that peat strength is strongly influenced by its stress history and also varies as a function of the water content and degree of decomposition (fibre content). The normally consolidated normalised strength ratio (s u /σ v ') from SS tests of peat was found to be approximately 0.4, which is towards the lower bound of previously published data for peat. Comparisons of strengths derived from SS and field vane tests showed the ratio of the strength derived from the two tests was influenced by the degree of decomposition and that previously published correction factors for field vane strengths are inappropriate. Guidance is given for engineers working on future schemes on upland peat areas.

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“…6. Undrained strength ratios were evaluated using the SHANSEP technique (Ladd, 1991) using triaxial testing, with the results shown in Figure 7. Those results were used to estimate pre-earthquake shear strengths beneath the affected structures, with the results in Figure 6.…”

Section: Laboratory Testingmentioning

confidence: 99%

“…Based on the ICU triaxial compression test results as indicated in Figure 7, the averaged undrained shear strength (s u ) of the upper 10 m clay is approximately 68 kPa. Considering the effects of anisotropy, the averaged undrained shear strength (s u-ave ) can be taken as 80% of the triaxial compression s u (Ladd, 1991), which is about 55 kPa. Using Vesic (1973) bearing capacity theory, the ultimate bearing capacity for the mat foundation is 350 kPa.…”

Section: Bearing Capacity Failure Potential Evaluationmentioning

confidence: 99%

Cyclic Softening of Low-Plasticity Clay and Its Effect on Seismic Foundation Performance

Chu

Stewart

Boulanger

et al. 2008

J. Geotech. Geoenviron. Eng.

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Significant occurrences of ground failure in the form of liquefaction, ground softening, and lateral spreading occurred in Wufeng, Taiwan during the 1999 Chi-Chi earthquake (M w = 7.6). The Wufeng region is located adjacent to the ruptured fault on the foot wall, and experienced peak accelerations ∼0.7 g. We describe the results of field investigations and analyses of a small region within Wufeng that exhibited a range of ground performance. The investigated region consists of an E-W trending line of 350 m length. The east end of the line is a residential area with single-story structures for which there was no surface evidence of ground failure. The west end of the line had 3-6 story reinforced concrete structures that were heavily damaged structurally, but which also underwent extensive foundation failures including differential settlement, foundation punching failures, and full foundation bearing failures. No ground failure was observed in the free-field at the west end of the line. Surficial soils consist of low-plasticity silty clays that extended to 8-12 m depth in the damaged area (west side), and 3-5 m depth in the undamaged area (east side). Analyses were performed of the potential for cyclic softening of the clays, which effectively investigates the potential for large cyclic shear strains to develop. The resistance of the clay to cyclic softening is evaluated using the results of material-specific strength testing (both monotonic and cyclic). The seismic demand applied to the soil is evaluated from ground response analyses (to investigate demand from ground shaking) as well as soil-structure interaction analyses (to investigate demand associated with base shears and moments in both six-and one-story structures). Results of the analysis indicate low factors of safety in foundation soils below the six-story building during earthquake shaking, which contributes to bearing capacity failures at the edges of the foundation due to rocking effects. Similar analyses indicate high factors of safety (above unity) in foundation soils below one-story buildings as well in the free field. Accordingly, analysis of the site within a framework that systematically accounts for the clayey nature of the foundation soils successfully predicted the field performance.

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Stability Evaluation during Staged Construction

Cited by 424 publications

References 66 publications

Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

Measurement, interpretation and recommended use of laboratory strength properties of fibrous peat

Evaluation of peat strength for stability assessments

Cyclic Softening of Low-Plasticity Clay and Its Effect on Seismic Foundation Performance

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