Geotechnical and Geological Studies of

Tunnelling

The foundation supporting a civil engineering structure is the most important element of the structure, and will have an affect on the quality, safety and construction costs of the project. Usually, the geotechnical properties of the foundations are determined through engineering geological surveys and ground investigations, prior to construction and will, in some cases, guide the planning and design.

Introduction………..

The geology along a tunnel alignment plays a dominant role in many of the major decisions that must be made in planning, designing, and constructing a tunnel. Geology dominates the feasibility , behaviour , and cost of any tunnel.

Although difficult to appreciate, the engineering properties of the geologic medium and the variations of these properties are as important as the properties of the concrete or steel used to construct the tunnel structure.

ROLE OF GEOTECHNOLOGY IN PLANNING

In a tunnel , the ground acts not only as the loading mechanism, but also as the primary supporting medium.

For the tunnel designer and builder, the rock or soil surrounding a tunnel is effectively a construction material.

Continue…..

Geotechnical Information is needed from the very moment planning begins on any tunnel project.

The earlier that definitive exploration is made, the greater freedom the owner and designer can have in their selection of alignment and construction methods, and, thus, the greater the potential cost savings.

Geotechnical information can be invaluable in the selection of the general corridor as well as the detailed alignment of a tunnel project.

GENERAL PRINCIPLES OF GEOTECHNICAL INVESTIGATIONS

Underground projects have vast uncertainty The cost, and indeed feasibility, of the project is

dominated by geology Every aspect of the geologic investigation for

tunnels is more demanding than investigations for traditional foundation engineering projects

Regional geology and hydrogeology must be understood

Groundwater is the most difficult condition/parameter to predict and the most troublesome during construction

The range of permeability is significantly greater than the range of any other engineering parameter

Selected Challenges of the Underground…………….

Even comprehensive exploration programs recover a relatively minuscule drill core volume that is less than 0.0005percent of the future excavated volume of the tunnel

Engineering properties change with a wide range of conditions, such as time, seasons, rate and direction of loading , etc.; sometimes drastically

It is guaranteed that the actual stratigraphy, groundwater flow, and behaviour observed during construction will be compared to your predictions.

Continue……..

It is important to predict the likely geological conditions ahead of the tunnel face. Various techniques are available to assist in these kinds of predictions. When the survey results are being utilized, the accuracy and reliability of the investigations must be evaluated sufficiently, because the characteristics of these investigations may vary by investigation principle or by characteristics of the research objects.

TUNNELLING GEOLOGICAL INFORMATION EVALUATION TECHNIQUE

The condition of headrace channel tunnel with large water inflow occurred under tunnel excavation is shown in Figure(Shiozaki et al., 2000). In this case the water inflow arose near the fractured zone which was not observed during the ground investigation, causing the tunnel face to collapse putting the excavation on a halt, introducing financial implications.

Furthermore, the amount of oxygen dissolved in the water inflow was rather small and the oxygen concentration in the tunnel was temporarily lowered to 16%, causing safety construction problems .

Case Study……….

A situation of drainage countermeasure in the tunnel:

The ground investigation flowchart for geological evaluation under tunnelling

NO

Yes

The outline of the case study of tunnelling information

Utilization of geological information based on TBM machine data

Geological structure prediction by seismic reflection method (called TSP method)

CASE STUDY OF TUNNELING INFORMATION

Case study on various ground investigation methods during tunnel construction was carried out in order to confirm the suitability of the evaluation flow. In this case, the established purpose of the ground investigation was to ensure the quality and safety under tunnel construction.

such as faults, fractured zones, water contained zones, large-scale cavities etc., became the researched survey object.

In this case study, the researched survey method includes a technique for estimating ground conditions near the tunnel face under construction by continuously collecting machine data of TBM, by TSP method – a kind of seismic reflection method carried out in tunnel.

The outline of the case study of tunnelling information

The TBM method is defined as machine controlled excavation of full cross section tunnelling methodTypical features of the TBM method are as following:- Since excavation cross section of the tunnel

is of a round shape, the stability of the tunnel wall is high due to the arch effect;

As the excavation energy is dispersed, there would be less damage to the tunnel wall.

Utilization of geological information based on TBM machine data

TBM method is a rational tunnelling method because the tunnel support work is minimum

Continue……………….

TBM Machine

it is unable of conducting geological observation of the tunnel face because the cutter head is fixed with a disk cutter, which is pressing against the tunnel face during the excavation. And keeping the excavation without understanding the change in the geology of the tunnel face may cause collapse of the tunnel face and the tunnel wall.

In excavation and construction of a tunnel using a TBM, the risk of accident is existed, though there is a merit for quality assurance, etc…

Therefore, it is important to reduce the risk of the TBM method by clarifying the ground conditions around and ahead of the tunnel face, and incorporating this information in the construction management plan.

Disadvantage of the TBM method:-

Evaluation flow of the TBM machine data…….

In evaluating the ground conditions according to the TBM machine data, each machine data item is subjected to examination:-

Cutter electric current: current of the cutter head rotating motor

Pure penetration rate: intrusion speed of the cutter head

Thrust: pressure of the promotion jack Bearing capacity: oil pressure of gripper jack

which ensures reaction force

Geological characteristic evaluation according to TBM machine data

a) Sheared off lining: it occurs for tunnel passing through active faults; b) Slopes failure induced tunnel collapse: it occurs when the tunnel

runs parallel to slopes generating landslides passing through the lining; c) Longitudinal cracks: it occurs when the tunnels subjected to higher

deformations due to surrounding ground; d) Traverse cracks: it occurs when the tunnel has weak joints; e) Inclined cracks: it occurs for a combination of longitudinal and

transversal cracks; f) Extended cracks: it occurs when there is the partial collapse of

linings for seismic intense deformation; g) Wall deformation: it occurs when there is a transverse reduction due

to the invert collapse; h) Spalling of lining: it occurs when the transversal section completely

collapses.

CRACK DISTRIBUTION ALONG THE TUNNEL LINING

Deformation modes of tunnels due to seismic wavesThe behaviour of a tunnel is sometimes approximated to that of an elastic beam subject to deformations imposed by the surrounding ground. Three types of deformations (Owen andScholl, 1981) express the response of underground structures to seismic conditions 1) axial compression and extension2) longitudinal bending3) ovaling/racking

carries out VSP exploration in the tunnel, and developed prospecting system called TSP202 including the data analysis software.

A receive point is set at 50m away from the tunnel face, and within this distance usually 24 shot points by explosion are set. Array measurement is carried out between the receiver and shot points. As an output in the TSP method may show the reflection event crossing position ahead of the tunnel face, the change of property of reflection plane can be judged from the change of the phase.

Geological structure prediction by seismic reflection method (called TSP method)

“IAEG2006 Paper number 716” “Tunneling information - An oriented construction technique using geological information”

“PLANNING AND SITE INVESTIGATION IN TUNNELLING” “Harvey W. Parker” Parker, Harvey W. (1996), Geotechnical Investigations, Chapter 4 of Tunnel Engineering Handbook,

2nd Edition, edited by Kuesel & King, Chapman & Hall, New York, 1996.   http://www-civ.eng.cam.ac.uk/geotech_new/people/bolton/geotechnology.html http://geology.com/articles/what-is-geology.shtml Research paper on “PLANNING AND SITE INVESTIGATION IN TUNNELLING” by “Harvey W.

Parker” Research paper on “Tunneling information - An oriented construction technique using

geological information” by“KAZUHIRO ONUMA, HIROYOSHI KASA, HIROYUKI YAMAMOTO and SHINJI UTSUKI”

Research paper on “Tunnels under seismic loading: a review of damage case histories and protection methods” by “ G. Lanzano+, E. Bilotta, G. Russo” Department of Hydraulic, Geotechnical and Environmental Engineering (DIGA).

(University of Naples Federico II, Italy and+ SAVA Department, University of Molise, Campobasso, Italy ).

Research paper on “Effects of Seismicity on Rock Support in Tunnels of Different Sizes” by “ Rajinder Bhasin & Amir M. Kaynia” (Norwegian Geotechnical Institute), “D.K.Paul, Y. Singh and Shilpa Pal” (Department of Earthquake Engineering, IIT, Roorkee)

Research paper on “Engineering Survey System for TBM (Tunnel Boring Machine) Tunnel Construction” by “Andrew Hung Shing Lee, Hong Kong”

References………….

Thank you……………. Any Questions???