Geotechnical Engineering

The existence of thick compressible clayey silt deposits along the Sava River provides major obstacle for design and construction of highway embankments in this region. To understand the consolidation and permeability characteristics of this alluvial layer and then to develop reliable soil parameters for earthwork design and construction, a comprehensive soil testing program was carried out. The program consisted of both in situ tests [e.g., standard penetration test borings, piezocone penetration test (CPT) soundings, Marchetti flat dilatometer test soundings, Lefranc test and CPT pore pressure dissipation tests] and laboratory tests (e.g., soil index tests, consolidation tests). The field and the laboratory test results showed that the clayey silt deposit was highly overconsolidated at the top and lightly overconsolidated at greater depths. The findings obtained from this study will be beneficial for future design and construction of Embankments along the Sava River.

The perception of geotechnical problems has, in recent years, been challenged by requirements for balance between traditional engineering and environment-friendly, sustainable solutions. Modern geotechnical engineers have to develop knowledge on the environment surrounding their solutions and thrive within the new discipline of environmental geotechnics. The general trends in the discipline are used as a background to personal experience to establish the place of a generic environmental geotechnics framework within the sustainable development area. Recent developments and potential future trends in areas that could be considered as part of environmental geotechnics are briefly outlined together with the need for training and education.

Remediation was designed for a marginally stable fill slope comprising up to 5 m loose cohesive fill in a residential area adjacent to a deep valley. Excessive ground settlements around a sewage pumping station (SPS) and a tension crack in the vicinity of residential houses in an area near Glasgow were linked to possible burst utilities and gradual washout of fines in the fill. Desk study and ground investigations were carried out to determine the site history and geological setting. Remedial options were considered. In light of confined site space and availability of materials, crushed compacted rock fill was considered the best option for replacement of the soft fill. Topsoil [150mm] was used to cover the rockfill and promote vegetation growth. The advantages of the rockfill over compacted cohesive fill include ease of construction, performance and suitability. Effective drainage including in-slope and contour channel drainage were designed to prevent build-up of pore water pressures in the slope beneath topsoil. Construction sequence including excavation and preparation of temporary cut, installation of drainage layer, deposition and compaction of rockfill material in layers, deposition and seeding of the topsoil layer, construction of permanent surface drainage system and maintenance access was also designed.

Plant root systems frequently permeate both natural and engineered soil slopes, influencing slope stability via mechanical reinforcement and soil drying. These root systems are often loaded by external forces during slope movements and when plant stems are subject to animal foraging or wind gusts. A series of physical model tests were conducted to examine how root geometries, root properties, and soil effective stress states affect the pullout capacity of simple unbranched model roots. Lengths of wood, rubber, and real roots were pulled from dry and partially saturated sand. The tests revealed the importance of the root to soil stiffness ratio during progressive failure, the mechanical properties of soil (and interfaces) at low effective stresses, the root diameter, and the tortuosity of the root material. Scaling issues due to shear banding are more important, and effective stresses under wet conditions are smaller than in conventional geotechnical practice because roots have a relatively small diameter (typically 10−4–10−1 m) and are at shallow depth (typically 0–2 m). After careful consideration of these effects, predictions were made for the pullout capacity of small root sections based on material data for willow roots (Salix viminalis) in sand.

Background
Plants alter their environment in a number of ways. With correct management, plant communities can positively impact soil degradation processes such as surface erosion and shallow landslides. However, there are major gaps in our understanding of physical and ecological processes on hillslopes, and the application of research to restoration and engineering projects.
Scope
To identify the key issues of concern to researchers and practitioners involved in designing and implementing projects to mitigate hillslope instability, we organized a discussion during the Third International Conference on Soil Bio- and Eco-Engineering: The Use of Vegetation to Improve Slope Stability, Vancouver, Canada, July 2012. The facilitators asked delegates to answer three questions: (i) what do practitioners need from science? (ii) what are some of the key knowledge gaps? (iii) what ideas do you have for future collaborative research projects between practitioners and researchers? From this discussion, ten key issues were identified, considered as the kernel of future studies concerning the impact of vegetation on slope stability and erosion processes. Each issue is described and a discussion at the end of this paper addresses how we can augment the use of ecological engineering techniques for mitigating slope instability.
Conclusions
We show that through fundamental and applied research in related fields (e.g., soil formation and biogeochemistry, hydrology and microbial ecology), reliable data can be obtained for use by practitioners seeking adapted solutions for a given site. Through fieldwork, accessible databases, modelling and collaborative projects, awareness and acceptance of the use of plant material in slope restoration projects should increase significantly, particularly in the civil and geotechnical communities.

Bervie Braes is a 750 m long, and up to 55 m high, coastal slope above a residential area and harbour in Stonehaven, Scotland, with a history of instability mostly associated with the road traversing the slope. This paper outlines the most probable causes of the instability on the slope and details the hazards that had to be taken into account during the design and construction of stabilisation measures. The hazards associated with hydrology in terms of future potential change in rainfall patterns and intensity, but also in terms of providing adequate drainage capacity and flows, were juxtaposed against the geotechnical hazards of shallow landslips and erosion near the surface, as well as deep-seated landslides on the slope. Owing to the complex nature of the hazards and the need for longer life expectancy of the design, the soil nailing option was combined with eco-engineering strategies to provide resilience for a changing climate. A risk-based approach considering the number of lives at danger during a catastrophic failure was adopted when deciding on the priority of the areas of the slope to be stabilised. The sustainability of the design solution and the construction methods were constantly monitored and re-appraised throughout the project.

Determination of optimal pavement structural thickness is a fundamental prerequisite to the achievement of a balanced Value Engineering (VE) design that culminates in enhanced structural performance as well as cost and construction time reduction. With increased socio-economic activities and rate of development, the demand on road and air transport and the reciprocal pavement structural performance requirements have become increasingly intensified. In this Study, a new mechanistic-empirically derived thickness-modulus ratio theory is introduced and applied in developing mechanistic model equations for determining the appropriate layer and full-depth pavement structural thicknesses required considering varying material properties, layer stiffness, loading factors and environmental conditions. The versatility and precision of this approach in achieving an optimal performance based balanced design for different pavement structural types under varying environmental conditions, is introduced. The dexterity and computerization advantages of the proposed approach are demonstrated  through an illustrative design example. 

The Limit Equilibrium method of analysis has a variety of advantages. However, this method requires a large amount of computation and an arbitrary iteration process for obtaining the overall minimum factor of safety. Within the iteration process, locating the critical slip surface is of the greatest essence.
The proposed method of embankment stability analysis provides a simplified approach of directly locating the critical slip surface on the basis of which the minimum Factor of Safety (FS) can be computed.
General solutions are developed for the rotational stability analysis of reinforced embankments with and without ground improvement constructed on soft ground that has an undrained shear strength varying with depth. The general cases of an embankment having a berm, dry or wet tensile cracks, and multiple layers of reinforcement are considered. The additional friction caused by the reinforcement force normal to the slip plane is incorporated into the solution. The solutions are presented in the form of simple equations. The relationship between the critical slip circles through the embankment with and without geosynthetics reinforcement is expressed explicitly. The simplified analysis procedures and supporting computational examples allow the user to obtain the solutions using hand computations. A simple computer program in the form of excel worksheets can be developed to quickly obtain the final results. Applications and illustrative examples of embankments reinforced with geosynthetics and steel strips, are given. In order to validate the effectiveness of the proposed method, comparative analyses are made with results obtained using other approaches. The results also compare very well to the solutions obtained from the method of slices using the computer programs SB-SLOPE  and PC-STABL6 for the geosynthetics reinforced embankment.

The degree of effective improvement of the OPMCS (Optimum Mechanical and Chemical Stabilization) technique in enhancing the vital geotechnical engineering properties of ground and geomaterials is illustrated through some typical results based on laboratory and in-situ experimental testing performed on various geomaterials within the East and Central African region. A case example of the most recent application of the OPMC technology in realizing Value Engineering (VE) design and construction of a runway pavement for the Isiolo International Airport in the Eastern State of Kenya is also provided, whilst case study analyses are carried out for a road pavement structure in Juba, a pad foundation in the Jonglei Flood Plains of Southern Sudan and a retaining wall along a steep slope in Addis Ababa, Ethiopia.
The results from this Study demonstrate that the degree of improvement of the consolidation properties, bearing capacity, shear strength and Young’s modulus (elastic stiffness) are mainly a function of the quantitative and qualitative level of OPMCS.

Within the framework of classical visco-elasto-plastic theory, the strength and yielding characteristics of geomaterials at relatively large strains are described by defining a yield locus whereby the behavior within this locus is considered either rigid, linear elastic or non-linear elastic. Nevertheless, recent research has shown that such simplifications are inadequate in characterizing the overall stress-strain behavior of geomaterials over a wide range and most researchers have proposed multiple kinematic yield surfaces to better describe the elasto-plastic behavior observed within the larger scale yield envelope.
As a consequence, most of the recent constitutive models describing the plastic behavior of geomaterials including clays, sands and soft rocks under cyclic loading are derived from the elasto-visco-plasticity theory along with the concept of the non-linear kinematic hardening rule. However, despite the various numerical and modeling research that has been undertaken, a quantitative method of determining the limiting boundaries of the sub-yield surfaces based on experimental test results has yet to be proposed.
In this Study, methods of determining sub-yield strain limits and multi-kinematic hardening sub-yield surfaces are proposed, their application introduced and a comparison of experimental and modeled results made.

One important measures of country’s development is the status of its roads. India is abundant in natural resource
but this situation can never be fully utilized by inferior quality and poorly maintained road system. India has the second
largest network of roads in the world. It is, however, also known for its poor roads. One of the elements by which the
public evaluates the quality of roads is the smoothness of pavements, for both the newly constructed and rehabilitated
pavements (Indian highways April 2008).
Realizing the benefits of concrete roads, the Ministry of Surface Transport of India has approved considerable
concrete road projects. High degree of evenness and better riding quality, together with long service life and minimum
maintenance costs have made it popular surfacing material throughout the world. There is no doubt about the importance
of obtaining improved pavement smoothness. Not only does it gives a better and safer ride, but also reduce the vehicle
maintenance cost and is better able to sustain heavy traffic load. Nor it is an unattainable goal with research backed
innovations in technology, equipment and materials offering a wide array options to choose from, the engineer is many
steps closer to the perfect pavements (Sharma 1998).
So the path to the perfect, problem free concrete pavement is by no means a smooth one, given the tough
standards tighter specifications on mat levelness being enforced today. Under the modern construction methodology, the
utilization of proper equipment is also equally important. However the engineer has at his command a battery of modern
technologies, innovations and automation in machinery like slip form pavers and all at the push of button. Slip-form
paving techniques are now more widely used for laying concrete pavements. This has enabled pavements to be laid more
quickly and more economically than in the early 1990’s, when more traditional paving techniques were still in use.
In this paper, the highly mechanized technique of construction of concrete pavement, known as slip form paving
has been addressed. Different stages and the critical factors during the paving operation are discussed in this paper. The
comparative study of different type of paving techniques for concrete pavement is also highlighted in the paper.

Keywords: Slip form Paver, dowel bar placing, trimming and leveling, confirming plate paver, oscillating beam type
paver.

ABSTRACT: In response to the growing importance of sustainable undertaking, purchasing and building,
designers, consultants and pavement managers now tend to make more rational decisions than before when
comparing the pros and cons of the construction, maintenance and management of various types of road
pavements. Asphalt and concrete pavements offer specific advantages that need to be compared when selecting
the most favorable option for long-life pavements. Financial decisions can be based on life cycle cost. Life Cycle
Cost analysis is to arrive at such an economic equitable assessment of competing design alternatives and it
further useful for budget planning. The paper describes life cycle cost analysis of the assets of road pavement by
using present worth method. The information regarding the user cost and vehicle operating cost as per IRC
recommendation is also discussed in detail.
KEYWORDS: Life cycle, life cycle management, life cycle costing, economic evaluation, present worth method,
vehicle operating cost.