Characterizing a weathering profile over the Kuantan Basalt

Three broad morphological zones can be differentiated; the top pedological soil (Zone I) being 3.60 m thick and comprising brown, soft to stiff, clays. The intermediate saprock (Zone II) is 1.12 m thick and consists of brown, very stiff, sandy silt with many lateritic concretions, whilst the bottom bedrock (Zone III) is an outcrop of vesicular olivine basalt with weathering along joints. Constant volume samples show the saprolite (sub-zone IC) to have dry unit weights of 11.78 to 12.80 kN/m3, whilst the solum (sub-zones IA and IB), and saprock, have values ranging from 10.65 to 11.09, and from 11.35 to 11.50, kN/m3, respectively. Porosities are variable; the saprolite with the lowest values of 52 to 56% and the solum and saprock with values of 57 to 60%. Clay and silt contents increase up the profile with a corresponding decrease in sand and gravel contents. Colloid (<1 μm size) contents especially increase up the profile from 10 to 15% in saprock through 30 to 40% in saprolite and exceeding 57% in the solum, These increasing colloid contents point to the increasing effects of pedological processes. Thin-sections of weathered rims (1-2 cm thick) show alteration of basalt to start with formation of micro-cracks (Stage 1) that become stained by secondary iron oxides and hydroxides. Decomposition of the essential minerals then occurs in the order: olivine (Stage 2), augite (Stage 3), and plagioclase feldspar (Stage 4). An increase in apparent porosity, but a decrease in unit weights and specific gravity, reflect these stages of weathering; the boundary between ‘rock’ and ‘soil’ material occurring when all olivine and augite crystals have decomposed. It is concluded that the weathering profile results from in situ alteration of basalt due to lowering of an unconfined groundwater table; pedological processes giving rise to further alteration.

Meaning, Measurement, and Field Application of Fully Softened Shear Strength of Stiff Clays and Clay Shales

Fully softened shear strength mobilized in first-time slope failures, introduced by Skempton in 1970, corresponds to a random edge-face arrangement and interaction of clay particles in an entirely destructured fabric of stiff clays and clay shales. A series of triaxial compression tests was conducted on reconstituted normally consolidated specimens of 15 stiff clay and clay shale compositions. Based on the laboratory results an empirical correlation for secant fully softened friction angle, ϕ'fssσ'n, was developed for clay compositions with plasticity index in the range of 10 to 250%, in effective normal stress range of 10 to 700 kPa. The laboratory measurements confirm an empirical equation for fully softened shear strength in terms of parameters ϕ'fss100 and mfs. The field application of secant fully softened friction angle was examined by stability analyses of 63 first-time slope failures in 38 geologic materials. These include 45 slope failures with a segment of observed slip surface at residual condition and the back-scarp mobilizing fully softened shear strength, and 18 slope failures with entire observed slip surface at fully softened condition. The back-calculated fully softened secant friction angles for first-time slope failures are in good agreement with ϕ'fssσ'n correlation based on laboratory tests.

Estimation of Distribution Factor for Peak Penetration Resistance Prediction of Spudcan Foundations in Loose to Medium-Dense Sand Overlying Clay

A series of 3D finite element (FE) analyses were performed to estimate the peak penetration resistance of spudcan foundations in sand over clay soil profiles. Elasto-perfectly plastic models following Mohr–Coulomb and Tresca failure criteria were used for sand and clay layers, respectively. The coupled Eulerian–Lagrangian (CEL) approach was used to simulate the large deformation in soil that occurs during the spudcan penetration. The performance of the numerical model was validated against centrifuge test results. A parametric study with a broad range of strength parameters for sand and clay was performed. The numerical results were used to assess the influence of sand thickness (Hs), the diameter of spudcan (D), friction angle of sand, and undrained shear strength of clay (su). A wide range of su was utilized to predict the resistance both of the soft and stiff clays. The calculated peak resistances are compared with a published analytical model. It is demonstrated that the model highly overestimates the peak resistance for stiff clays, most likely because it was developed specifically for soft clays and, therefore, does not account for the influence of su. One of the parameters of the model is revised to account both for su. Comparisons highlight that the modified model is able to capture the simulated peak penetration resistance for both soft and stiff clays.

Impact of Pile Punching on Adjacent Piles: Insights from a 3D Coupled SPH-FEM Analysis

Pile punching (or driving) affects the surrounding area where piles and adjacent piles can be displaced out of their original positions, due to horizontal loads, thereby leading to hazardous outcomes. This paper presents a three-dimensional (3D) coupled Smoothed Particle Hydrodynamics and Finite Element Method (SPH-FEM) model, which was established to investigate pile punching and its impact on adjacent piles subjected to lateral loads. This approach handles the large distortions by avoiding mesh tangling and remeshing, contributing greatly high computational efficiency. The SPH-FEM model was validated against field measurements. The results of this study indicated that the soil type in which piles were embedded affected the interaction between piles during the pile punching. A comprehensive parametric study was carried out to evaluate the impact of soil properties on the displacement of piles due to the punching of an adjacent pile. It was found that the interaction between piles was comparatively weak when the piles were driven in stiff clays; while the pile-soil interactions were much more significant in sandy soils and soft clays.

Measured earth pressures behind an integral bridge abutment

<p>Integral bridges are preferred by bridge authorities and road agencies because they provide a simpler form of construction, with reduced maintenance costs as a result of the elimination of bridge bearings and joints. This simpler construction brings with it design challenges as both the structure and the adjacent fill are constantly moving. Thermal expansion and contraction of the deck causes the abutments to move, leading to changes in pressure in the earth fill behind the abutment. The soil adjacent to the abutment accommodates the cyclic deck expansion and contraction caused by changes in bridge deck temperature. This results in an increase in the stiffness of the fill due to densification. Even if the fill is placed in a loose condition, it will be densified during the lifetime of the structure. The build‐up of pressure depends on the nature of the fill behind the abutment and on the type of abutment. Stiff clays show a relatively low build‐up of lateral stress however sand stresses can increase beyond at‐rest pressure and approach full passive pressures. Much of the research on this type of soil structure action has been done in the laboratory with limit conclusive field testing.</p><p>In this paper earth pressures measured over a 2 year period on a 90m long fully integral bridge are summarized and discussed in relation to measured changes in effective bridge temperature as well as the abutment movement, thus testing the hypothesis that when more strain (i.e. a longer bridge and/or increase in the change in effective bridge temperature) is imparted to the soil, more granular flow occurs, resulting not only in more rapid stress escalation, but also in higher earth pressures.</p>