Alec M. Marshall

Tunnel-Pile Interaction Analysis Using Cavity Expansion Methods

AbstractEvaluation of the impact of tunnel construction on existing buried structures is an important problem. This paper presents an analytical method for estimating the effect of tunnel construction on end-bearing piles located above the tunnel. The method can be used to estimate the safe relative distance between existing piles and newly constructed tunnels. Spherical and cylindrical cavity expansion/contraction analyses are used to evaluate pile end-bearing capacity and the reduction of confining pressure at the pile tip that results from tunnel volume loss. Pile end-bearing capacity is then reevaluated based on the reduced confining pressure at the pile tip. A modified shear modulus is used to account for the effect of pile installation on soil stiffness. The method is used to analyze centrifuge experiments conducted to study this problem. For the experimental data, where the service load applied to the piles during tunnel volume loss ranged between 50 and 60% of the maximum jacking force, the analyt...

Interpretation of Cone Penetration Test Data in Layered Soils Using Cavity Expansion Analysis

Cavity expansion theory plays an important role in many geotechnical engineering problems, including the cone penetration test (CPT). One of the challenges of interpreting CPT data is the delineation of interfaces between soil layers and the identification of distinct thin layers, a process which relies on an in-depth understanding of the relationship between penetrometer readings and soil properties. In this paper, analytical cavity expansion solutions in two concentric regions of soil are applied to the interpretation of CPT data, with a specific focus on the layered effects during penetration. The solutions provide a large-strain analysis of cavity expansion in two concentric regions for dilatant elastic-perfectly plastic material. The analysis of CPT data in two-layered soils highlights the effect of respective soil properties (strength, stiffness) on CPT measurements within the influence zones around the two-soil interface. Results show good comparisons with numerical results and elastic solutions. A simple superposition method of the two-layered analytical approach is applied to the analysis of penetration in multilayered soils. A good comparison with field data and numerical results is obtained. It is illustrated that the proposed parameters effectively capture the influence of respective soil properties in the thin-layer analysis. It is also shown that results based on this analysis have better agreement with numerical results compared with elastic solutions.

Design Oriented Linear-Equivalent Approach for Evaluating the Effect of Tunneling on Pipelines

AbstractThe process of tunneling is associated with ground movements which may lead to stressing of nearby existing buried infrastructure, and potentially poses a risk of damage. The need for an effective evaluation method of the potential risk increases with the ongoing expansion of underground space utilization. This paper presents a new approach for evaluating the interaction between an assumed input of greenfield tunneling displacements and an existing buried pipeline. The approach integrates new developments with previous research findings to establish a practical interaction analysis methodology that can be used in design. It involves the use of an elastic-continuum analysis to solve the soil-pipeline interaction together with an iterative calculation of the equivalent stiffness in order to consider soil nonlinearity. A set of simplified closed-form expressions, which can be used to evaluate maximum pipeline bending moments within the suggested framework, are presented in the paper. A comparison of ...

Effect of Relative Density on Settlements above Tunnels in Sands

This paper presents centrifuge experiment data related to the problem of tunnelling-induced ground displacement in sand. The paper focuses on the examination of the effect that relative density has on greenfield soil displacements above tunnels in sandy ground. Data from a series of plane strain centrifuge tests on tunnels in silica sand are presented. The relative density of the sand ranged from 50% to 90% in the tests. The soil displacement data were obtained using an imaged-based deformation measurement technique and examined to determine features of greenfield settlement, both surface and subsurface. The effect that relative density has on the settlement trough shape is demonstrated and discussed.

Benefits of Global Standards on the Use of Optical Fiber Sensing Systems for the Impact of Construction of New Utilities and Tunnels on Existing Utilities

Distributed Optical Fiber Sensing is a mature technology given its strong record of over 20 years. Nevertheless, underground utilities are yet to embrace it as an everyday tool despite its enormous capability. One dimensional long buried utilities and tunnels offer the best application for the use of this technology. Research studies around the world offer the promise of this technology in monitoring the impact of ground movements on underground utilities and tunnels. No application standards existed that governed the use of this technology within any jurisdiction in the world in September 2012. A global task group on optical fiber sensing systems (OFSS) was born to become a unique pool of talent and experience on the subject with over 40 leading experts from 17 countries, which went on to author two companion standards American Society for Testing and Materials (ASTM) F3079-14 and F3092-14, within ASTM Technical Committee F36. This paper provides a brief overview of how OFSS work, what is in these standards, why OFSS is poised to become the most versatile innovation among all measurement tools for field monitoring, what problems the task group faced during the development of the standards and how the members of the task group resolved these problems, what the benefits are of such global standards and the future plans for the global OFSS task group. The most paramount goal of the authors is to share the lessons they learned during the development of the standards with the delegates of this conference.

Discussion of “Observation of Ground Movement with Existing Pile Groups Due to Tunneling in Sand Using Centrifuge Modelling” by Ittichai Boonsiri and Jiro Takemura

This discussion aims to highlight the underlying cause of several aspects of the greenfield settlement data presented by Boonsiri and Takemura (Geotech Geol Eng 33(3):621–640, 2015). The discussion considers, for the geotechnical centrifuge tests that were reported, the effects of the boundary conditions imposed at the model tunnel on resulting settlements. Data obtained using the rigid boundary model tunnel in Boonsiri and Takemura (Geotech Geol Eng 33(3):621–640, 2015) are compared against other available data from tests using a fluid-filled flexible membrane model tunnel. It is demonstrated that the boundary conditions used to simulate tunnel ground loss have an important impact on the settlement mechanism; compared to a fluid-filled flexible membrane, a rigid boundary model tunnel results in wider settlement troughs, which do not vary in shape considerably with changes in relative tunnel depth, and can result in higher ratios between the area of the settlement troughs and the tunnel ground loss. The appropriateness of the different tunnel boundary conditions is also discussed.

An Experimental Evaluation of the Weathering Effects on Mine Shaft Lining Materials

Many shaft collapses are related to the deterioration and failure of the masonry shaft lining materials. In modern mine shaft, concrete is widely used to provide support. To analyse shafts stability, the properties of the lining need to be well defined. The behaviour of masonry and concrete can be considerably affected by long-term exposure to harsh mine water. This paper presents a study which focuses on the weathering effects of mine water on lining materials (brick, mortar, and concrete). To reproduce the weathering process, samples were placed into solutions of potable water, artificial mine water, and a more aggressive mine-water solution for just less than one year. Four phases of laboratory tests were conducted throughout the time period to assess the degradation of mechanical properties of the lining materials. Particular attention is given to the degradation of material strength and stiffness. Results indicate that the harsh acidic mine water has pronounced detrimental effects on the strength and stiffness of mortar. The weathering process is shown to have the most significant effect on the stiffness of concrete and mortar. It is also shown that the use of mass loss as an index for evaluation of mechanical properties may not be appropriate.

Centrifuge Model Tests of Rainfall-Induced Landslides

Rainfall-induced landslides and debris flows constitute very serious threats to human lives and infrastructure. In many cases, rainfall characteristics which cause the initiation of landslides are not very well determined and this might lead to the misunderstanding of the failure mechanism, the kinematic characteristics and the run-out distance of the failure. In this paper, the design of three series of centrifuge model tests on soil slopes, subjected to rainfall conditions, is presented. The main goal is to investigate rainfall characteristics which cause failure initiation in soil slopes in respect to soil properties and slope geometry. Tests will be performed in a geotechnical centrifuge at the Nottingham Centre for Geomechanics (NCG) under very well defined initial and boundary conditions. For the accomplishment of these tests, a climatic chamber has been developed which accommodates plane-strain slope models and sufficient instrumentation and embodies a rainfall and an evaporation simulation systems. During the centrifuge tests, changes in pore water pressures and soil state as well as deformations of the slopes will be measured, while rainfall intensity and total rainfall will be accurately defined. Three different soil types will be used to create uniform slope models, i.e. fine sand, silty clay and clay, while rainfall intensity will be proportional to the infiltration capacity. The paper describes, also, the saturation and calibration of Druck PDCR-81 miniature pore pressure transducers and SWT5 tensiometers used for pore water pressure measurements.

Centrifuge model study of thresholds for rainfall-induced landslides in sandy slopes

Rainfall-induced landslides are very common natural disasters which cause damage to properties and infrastructure and may result in the loss of human life. These phenomena often take place in unsaturated soil slopes and are triggered by the saturation of the soil profile due to rain infiltration which leads to the decrease of effective stresses and loss of shear strength. The aim of this study is to determine rainfall thresholds for the initiation of landslides under different initial conditions. Model tests of rainfall-induced landslides were conducted on the Nottingham Centre for Geomechanics geotechnical centrifuge. Initially unsaturated plane-strain slope models made with fine silica sand were prepared at varying densities at 1g and accommodated within a centrifuge container with rainfall simulator. During the centrifuge flight at 60g, rainfall events of varying intensity and duration, as well as variation of groundwater conditions, were applied to the slope models with the aim of initiating slope failure. This paper presents a discussion on the impact of soil state properties, rainfall characteristics, and groundwater conditions on slope behaviour and the initiation of slope instability.

Implementation of Advanced Constitutive Models for the Prediction of Surface Subsidence After Underground Mineral Extraction

Surface subsidence is a typical problem for any underground mineral extraction. In order to choose an appropriate method of extraction, predict damage to infrastructure and other unwanted consequences of surface subsidence, it is necessary to model the surface settlement. Previous research has shown that the conventional constitutive models, which are built into commercial software, encounter considerable difficulties when attempting to predict subsidence troughs. The troughs should be modelled deeper and narrower.