Joshua R. Omer

Large-scale pile tests in Mercia mudstone: Data analysis and evaluation of current design methods

Full-scale load tests were carried out on six instrumented large diameter bored, cast in-situ piles formed in Mercia mudstone, as part of the design of a new Viaduct in Cardiff, UK. In this paper, the results from six test piles and extensive data from 218 ground investigation boreholes are systematically processed in order to study the load transfer and resistance mechanisms in Mercia mudstone. Data from strain gauges embedded in each pile are first analysed to calibrate the load-deformation relationship of each pile as-built, taking into account (i) the non-linearity of concrete and (ii) the effect of partial steel encasement on pile stiffness at various levels. The shaft and base capacity of the piles are each predicted using 10 calculation methods belonging to the four basic categories: (i) Undrained analysis, (ii) Drained analysis, (iii) Mixed approach and (iv) Empirical correlation. It is found that the shaft capacity prediction methods are moderately consistent. The standard deviations of the ratio Qsp/Qsm of predicted to observed shaft capacity lies in the range 0.06–0.24. However, 8 of these methods are over-conservative, giving Qsp/Qsm values in the range 0.29–0.67. The remaining two methods yield Qsp/Qsm = 1.01 and 1.49. In contrast, the prediction methods for base capacity are found to be much less consistent. The ratio Qbp/Qbm of predicted to measured base capacity falls in the interval 0.52–1.93, with corresponding standard deviations of 0.16–0.82.

Compaction assessment of recycled aggregates for use in unbound subbase application

AbstractStudy was recently conducted at Kingston University to assess the suitability of using recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) in unbound subbase mixtures. The results showed that the use of 100% recycled aggregates increased the optimum moisture content and decreased the maximum dry density of the sub-base materials in comparison with natural aggregates. Moreover, the replacement of RCA by reclaimed asphalt pavement by 50% decreased the optimum moisture content and increased the maximum dry density in proportion to 100% RCA. The effects of physical properties on 0% air void and compaction curve were discussed for each type of subbase. The CBR values of the subbase materials prepared with 100%RCA is lower than subbase mixture with 100% natural aggregates. The CBR further decreased for replaced subbase with RAP so that 50%RCA + 50%RAP is not suitable for unbound subbase from the point of CBR view. In each mix the trend of CBR value was investigated in terms of water c...

Water Absorption Study Recycled Aggregates for Use Pavement Material

Water absorption properties of recycled materials play an important role in pavement performance. The performance of aggregates changes after absorbing water, then it affects highways layers such as base, subbase, capping. This is why these materials must comply requirements of codes and standards. With regard to the increasing trend of application of recycled aggregates in highways layers, this issue needs more investigation. This research is only a part of our large research programme on three different purposed mixes of unbound subbase mixture below: 1) 100% Recycled Concrete Aggregate (RCA); 2) 100% Lime Stone (NA); 3) 50% RCA + 50% Re-claimed Asphalt Pavement (RAP). Water absorption for each mix has been performed in different size fraction with pyknometer and wire basket methods. The relationship between density, grading and water absorption and its comparison for mixes would be indicating the changes in behaviour of aggregates and future performance of subbase. Laboratory testing showed that 100% Lime Stone had the higher densities than other mixes and water absorption value of 100% RCA was about 40% higher than 50% RCA + 50% RAP in 31.5 mm - 4 mm fraction.

Finite elements analysis of an underground collector installed by pipe-jacking method

Using the commercial software RS2, a 2D finite-element program for soil and rock application, the ground response to pipe jacking in pipeline installation in Avilés (north coast of Spain) was analysed. The geology of the location comprises Quaternary deposits on both flanks of the Avilés estuary and includes different highly variable geotechnical behaviour. Both axisymmetric and plane strain analyses were carried out in RS2 to simulate in 3D the ground response to pipe advancement. The results demonstrate that the vertical displacements at specific positions in the immediate vicinity of the pipeline were small. The maximum deformation at ground surface was shown to be less than 1.5 mm, which was still safe. However, the displacements were found to vary depending on the local properties of the materials drilled. Stress distributions were also computed.

Use of granulated blast furnace slag and lime in cement-bentonite slurry wall construction

This paper describes an experimental investigation on the use of ground granulated blast furnace slag (GGBFS) and lime as stabilizers for cement-bentonite (CB) slurry used in constructing vertical barrier walls. The primary objective is to develop a blended material, which can reduce the permeability and also enhance the strength of CB slurry walls with a shortened curing time. Mixtures comprising various proportions of cement, bentonite, GGBFS, and lime were prepared and tested for particle size distribution (PSD), liquid limit, plastic limit, permeability, unconfined compressive strength (UCS), and constrained modulus. For each mixture, the effect of varying curing time on the results of the aforementioned tests was also investigated. The research results demonstrate that blending CB with optimum fractions of GGBFS and lime lead to decreased permeability and increased UCS of the mixture, without any adverse consequences. Thus, subject to satisfaction of other requirements, it is concluded that a potentially superior material for constructing slurry walls can be achieved by using CB-GGBFS-lime blended mixtures.

3D finite element assessment of the effects of energy loops on the load capacity and settlement of bored piles installed in sand

Three-dimensional finite element analyses were carried out to study the geotechnical behaviour of piles fitted with high-density polyethylene (HDPE) tubes as energy loops for harnessing ground heat. The objective was to examine whether the existing analysis methods for conventional piles are applicable to energy piles. Using PLAXIS 3D software, simulations were done for 60 cases of energy piles comprising variously configured HDPE tubes. It was found that HDPE tubes inevitably interact with the soil around the pile such that 6–11 HDPE tubes decreased the load capacity by 18–70%, while 3–4 HDPE tubes had an optimum reinforcing effect on the soil, thereby increasing the load capacity by 30–75% depending on the pile size. However, the tubes had little effect on settlement at ultimate load. Thus, the work highlighted the limitation of conventional methods of analysis and the geotechnical effect of HDPE tubes installed to protrude from the base of an energy pile.

Laboratory simulation of the influence of groundwater rise and drip irrigation on the settlement of a sample of collapsible desert soil

Most types of sand have low susceptibility to settlement when in dry, dense and well-graded states but certain sands, when saturated, exhibit a decrease in suction and tensile strength hence leadin...

Laboratory Simulation of Irrigation-Induced Settlement of Collapsible Desert Soils Under Constant Surcharge

The heterogeneous nature of soil as a load bearing material, coupled with varying environmental conditions, pose challenges to geotechnical engineers in their quest to characterize and understand ground behavior for safe design of structures. Standard procedures for checking bearing capacity and settlement alone may sometimes be insufficient to achieve an acceptable degree of durability and in-service performance of a structure, particularly under varying environmental conditions, whether natural or man-made. There exists a wide variety of problematic soils that exhibit swelling, shrinkage, dispersion and collapse characteristics occasioned by changes in moisture content. Specific examples are collapsible soils, which occur mainly in arid and semi-arid regions, are generally capable of resisting fairly large loads in the dry condition but suffer instability and significant strength loss when in contact with water. A number of case studies in the United Arab Emirates were examined, where lightly loaded structures such as boundary walls, pavements and footpaths had been built on ground overlying collapsible soil strata. Sustained irrigation of the dry landscapes was found to have caused uneven settlement of the collapsible soils leading to continuous distress to the structures as evident from cracking and deformation. To help address the problem, an opportunity has been taken to develop a laboratory method of simulating the loaded behavior of collapsible soils in varying situations and to measure its deformation at constant surcharge and ground water infiltration rates. Finally, relationships were developed to estimate the time and magnitude of settlement, if thickness of collapsible soil is known.

Evaluation of Finite Element, Finite Difference and Elasticity Methods for Hypothetical Raft Foundations Installed on Layered Strata

Different numerical methods including 2-D finite element (FE) analysis were implemented for hypothetical raft foundations of high length/breadth ratios to evaluate the reliability of (1) Boussinesq’s method, (2) “rigid-punch” (RP) elastic methods and (3) finite difference (FD) incorporating subgrade reaction theory. A dedicated computer program was developed and used in addition to professional software packages to analyse uniformly loaded rafts of various length/width ratios and stiffnesses, interacting with multi-layered soils of different properties. It was found that the greater the flexibility of the raft the closer was the agreement between the deformations computed from FE and FD methods and the settlements predicted from FE and RP methods. Additionally, the FE method yielded the most realistic predictions principally because of its capability to model and account for the interactions between soil layers as well as the continuity of the soil support. The results revealed that soil stresses computed from elastic methods were inaccurate in cases where a relatively incompressible bedrock existed within depths equivalent to 4 times the raft width or less. This led to a recommendation that in order to predict raft deformations accurately, only those methods that account for both soil-structure and soil–soil interaction should be used in designing raft foundation in practice.

Computerised processing of ground investigation data and use in predicting the load-settlement behaviour of piled foundations

A new computer program “PILESET” is developed for use in predicting the bearing capacity and load-settlement behaviour of axially loaded single piles. The program can analyse almost any soil profile and accommodates (a) displacement piles (b) replacement (c) friction piles, (d) end-bearing piles, (e) under-reamed piles and (f) partially sleeved piles. A variety of soil input data can be used, including: (i) standard penetration tests, (ii) cone/piezo-cone tests, (iii) pressure-meter tests and (iv) laboratory tests. The above data types can be combined, if desired, for pile analysis by PILESET. The program calculates the shaft and base capacities of a pile based on 23 methods published in design guides in over 10 European countries. PILESET also predicts the pile load-settlement curve using five published methods, which include two modified load transfer (t-z) approaches formulated by the author. To demonstrate the capabilities of the program, analysis is carried out for case study involving seven full-scale screw piles formed in sand and tested to failure. In each case, the load-settlement curve computed using the author’s modified method in PILESET is found to be in excellent agreement with the actual pile test results.