This paper presents a piecewise-linear finite-difference model for one-dimensional large strain consolidation called CS2. CS2 is developed using a fixed Eulerian co-ordinate system and constitutive relationships which are defined by discrete data points. The model is dimensionless such that solutions are independent of the initial height of the compressible layer and the absolute magnitude of the hydraulic conductivity of the soil. The capability of CS2 is illustrated using four example problems involving small strain, large strain, self-weight, and non-linear constitutive relationships. In each case, the performance of the model is comparable to other available analytical and numerical solutions. Using CS2, correction factors are developed for the conventional Terzaghi theory which account for the effect of vertical strain on computed values by elapsed time and maximum excess pore pressure during consolidation. © 1997 John Wiley & Sons, Ltd.

Cs2: a piecewise-linear model for large strain consolidation

A new desiccation theory is developed that provides a rational framework for the consolidation and desiccation analysis of soft fine-grained waste soils. The theory includes four consecutive segments that correspond chronologically to the phases that a soft soil layer undergoes in the field after deposition: consolidation under one-dimensional compression; desiccation under one-dimensional shrinkage; propagation of vertical cracks and tensile stress release; and desiccation under three-dimensional shrinkage. A general form of the finite strain governing equation of the overall consolidation and desiccation process is formulated. It includes the cracking function and the nonlinear constitutive relations. The experimentally obtained consolidation and desiccation characteristics for soft china clay, which are needed for the overall analysis of a given field problem, are presented. The predictions of this theory for the response of a hypothetical soft china clay layer undergoing self-weight consolidation, see...

Desiccation theory for soft cohesive soils

Improving the traditional earth construction: a case study of Botswana

In this paper a new empirical relation between the unconfined compressive strength of intact rock and the end bearing capacity of drilled shafts in rock is developed. In addition, an analytical relation between rock mass strength and end bearing capacity is developed to explicitly consider the effect of discontinuities. Specifically, a database of 39 load tests is used in this paper to derive the new relation between end bearing capacity and unconfined compressive strength of intact rock. The derived relation indicates that the end bearing capacity factor, Nc, which is the ratio of the end bearing capacity, qmax, and the unconfined compressive strength, σc, of intact rock, decreases with increasing σc. This is in contrast to many existing relations assuming constant Nc values. Since this new empirical relation is derived from the results of load tests, the effect of discontinuities is implicitly considered. To explicitly study the effect of discontinuities, an analytical relation based on the Hoek-Brown s...

End Bearing Capacity of Drilled Shafts in Rock

Assessment of the stability of a dispersive soil treated by alum

Residual soils are products of chemical weathering and thus their characteristics are dependent upon environmental factors of climate, parent material, topography and drainage, and age. These conditions are optimized in the tropics where well-drained regions produce reddish lateritic soils rich in iron and aluminum sesquioxides and kaolinitic clays. Conversely, poorly drained areas trend towards montmorillonitic expansive black clays. Andosols develop over volcanic ash and rock regions and are rich in allophane (amorphous silica) and metastable halloysite. The geological origins greatly affect the resulting engineering characteristics. Both lateritic soils and andosols are susceptible to property changes upon drying, and exhibit compaction and strength properties not indicative of their classification limits. Both soils have been used successfully in earth dam construction, but attention must be given to seepage control through the weathered rock. Conversely, black soils are unpopular for embankments. Lateritic soils respond to cement stabilization and, in some cases, lime stabilization. Andosols should also respond to lime treatment and cement treatments if proper mixing can be achived. Black expansive residual soils respond to lime treatment by demonstrating strength gains and decreased expansiveness. Rainfall induced landslides are typical of residual soil deposits.

Geotechnical Characteristics of Residual Soils

Large deformation consolidation computer programs are being used extensively by Florida phosphate mining industries for compliance with regulatory activities. Accordingly, a prediction symposium was held to provide a forum of idealized boundary conditions that would demonstrate areas of agreement and the limitations of various computer programs. Nine different program users provided predictions of pond elevation histories and of pore pressure and void ratio profiles after one year for four different waste clay disposal scenarios. Programs to estimate quiescent consolidation of waste ponds having uniform initial void ratios, with or without surcharge loading, and continuous and/or stage filling are available, but less available are programs that handle nonuniform void ratios and/or multilayer conditions with different nonlinear compressibility properties. Presently, piecewise linear programs appear best suited to accommodate the latter. In general, final height predictions for all scenarios were in agreeme...

SOA: Large Strain Consolidation Predictions

A number of currently employed mathematical formulations used in modeling onedimensional quiescent consolidation of phosphatic waste clay ponds are reviewed. It is shown theoretically, as well as t...

Quiescent Consolidation of Phosphatic Waste Clays

Increased usage of drilled shafts to carry high‐foundation loads has resulted in the common practice to socket the shafts into bedrock to transmit these loads. However, end‐bearing uncertainties have lead various designers to rely solely upon skin friction within the sockets to transmit the loads. This paper reviews several design techniques/correlations to estimate rock/shaft friction values from lab tests. These methods rely upon: (1) Unconfined compression (q1) and (2) split tensile (q1)+qu tests on recovered rock cores to estimate the rock shear transfer values. A database of 14 field‐load tests compares the measured versus estimated rock shear values for the various methods, and suggests that a two‐parameter model (qu+qt tests) provides the best estimate or socket friction. A small‐scale field “pull‐out” test on grout anchors is suggested as an alternative method for estimating rock/shaft friction values.

Design of Socketed Drilled Shafts in Limestone

An approach is presented for the analysis of linear and nonlinear response of vertically loaded pile groups. The piles are modeled with finite elements, the pile-soil influence through load-transfer curves and the pile-soil-pile interaction through Mindlin's solution. Good agreement was obtained with the proposed method and elastic results and two recently completed field studies.

F. C. Townsend

Papers

Geotechnical Characteristics of Residual Soils

SOA: Large Strain Consolidation Predictions

Quiescent Consolidation of Phosphatic Waste Clays

Design of Socketed Drilled Shafts in Limestone

Numerical Analysis of Vertically Loaded Pile Groups