The shear strength of liquefied soil, su(LIQ), mobilized during a liquefaction flow failure is normalized with respect to the vertical effective stress (σ 'vo) prior to failure to evaluate the liquefied strength ratio, su(LIQ)/σ 'vo. Liquefied strength ratios mobilized during 33 cases of liquefaction flow failure are estimated using a procedure developed to directly back-analyze the liquefied strength ratio. In ten cases, sufficient data regarding the flow slide are available to incorporate the kinetics, i.e., momentum, of failure in the back-analysis. Using liquefied strength ratios back-calculated from case histories, relationships between liquefied strength ratio and normalized standard penetration test blowcount and cone penetration test tip resistance are proposed. These relationships indicate approximately linear correlations between liquefied strength ratio and penetration resistance up to values of qc1 and (N1)60 of 6.5 MPa and 12 blows/ft (i.e., blows/0.3 m), respectively.Key words: liquefaction, flow failure, liquefied shear strength, stability analysis, kinetics, penetration resistance.

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This paper presents recommendations for selecting the type and magnitude of drained shear strength parameters for analysis of landslides. In particular, the importance, existence, and use of the cohesion shear strength parameter is reviewed. For slope stability analyses, it is recommended that the shear strength be modeled using a stress dependent failure envelope or a friction angle that corresponds to the average effective normal stress acting on the slip surface passing through that particular material instead of using a combination of cohesion and friction angle to represent soil shear strength. Other recommendations for stability analyses include using an effective stress cohesion of zero for residual and fully softened strength situations. To facilitate selection of shear strength parameters for landslide analyses, empirical relationships for the drained residual and fully softened strengths are updated from the previous empirical relationships presented by Stark and Eid. Finally, the paper presents torsional ring shear test results that indicate that pre-existing shear surfaces exhibit self-healing that results in increased shear resistance. The magnitude of healing appears to increase with increasing soil plasticity, and this increase could have implications for the size, timing, and cost of landslide remediation.

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Relationships between cone penetration tip resistance and the liquefaction potential of sandy soils are presented to facilitate use of the cone penetration test (CPT) in liquefaction assessments. The relationships are based on 180 liquefaction and nonliquefaction field case histories where CPTs were performed and illustrate the importance of median grain size and fines content on liquefaction resistance. The proposed CPT-based relationships were developed to describe the field case histories where CPT data are available, and eliminate the need to rely on conversions of standard penetration test (SPT) blow counts to CPT tip resistance used by existing CPT liquefaction-potential relationships. A new conversion between CPT tip resistance and SPT blow count is also proposed using the liquefaction-potential relationships developed from CPT data and existing liquefaction-potential relationships developed from SPT data. Finally, tentative CPT based liquefaction-potential relationships are proposed for clean and silty gravel based on 18 liquefaction and nonliquefaction case histories.

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Slope inclinometers/indicators are used to determine the magnitude, rate, direction, depth, and type of landslide movement. This information is usually vitally important for understanding the cause, behavior, and remediation of a landslide. However, many inclinometer measurements fail to achieve these intended aims because of lack of appreciation of the many factors that need to be correctly implemented during installation, monitoring, and data reduction to yield useful data. This paper presents some guidelines for understanding, installing, and interpreting slope inclinometers and presents three case histories that illustrate some of the pitfalls that can develop if these guidelines are not followed.

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