Tunneling in weak Rocks by Singh and Goel

Hi,
 This book by Bhawani Singh and Rajnish K. Goel is a very easy to read and useful book for the students of the UG and PG courses of Geo-technical Engineering. I got this book from my course teacher, and it is very helpful.

In this post, I want to share with you the quotes those are written in the book, at the bottom of every title line at the start of the new chapter.
I loved these quotes, and they somehow motivated me to read this book.


1. (Chapter No.1 INTRODUCTION)
"College is where you learn how to learn" - Socrates (470 - 399 B.C.)

2. (Chapter No.2  Applications of Geophysics in tunneling and site survey activities)
"And so Geology once considered mostly a descriptive and historical science has in recent years taken on the aspect of an applied science. Instead of being largely speculative as perhaps it used to be, geology has become factual, quantitative, and immensely practical. It became so first in mining as an aid in the search for metals; then in the recovery of fuels and the search for the oil; and now in engineering in the search for the more perfect adjustment of man's structure to nature's limitations and for greater safety in public works." -  Charles P. Berkey, Pioneer Engineering Geologist. 

3. (Chapter No.3 Terzaghi's Rock Load Theory)
"The Geological engineer should apply theory experimentation but temper them by putting them into the context of the uncertainty of nature. Judgement enters through engineering." - Karl Terzaghi

4. (Chapter No.4 Rock Mass Rating (RMR))
"Effectiveness of knowledge through research(E) is E = mc^2; where m is the mass of knowledge and c is communication of knowledge by publications."   - Z.T. Bieniawski

5. (Chapter No.5  Rock Mass Quality Q)
"Genius is 99 percent perspiration and 1 percent inspiration." - Bernard Shaw

6. (Chapter No.6  Rock Mass Number)
 " My attention is now entirely concentrated on rock mechanics, where my experience in applied soil mechanics can render useful services. I am more and more amazed about the blind optimism with which the younger generation invades this field, without paying any attention to the inevitable uncertainties in the data on which their theoretical reasoning is based and without making serious attempts to evaluate the resulting errors."     - Annual summary in Terzaghi's Diary

7. (Chapter No.7 Strength of Discontinuities)
"Failure is success if we learn from it."  - Malcom S. Forbes

8.(Chapter No.8 Strength enhancement of rock mass in tunnels)
 "The behaviour of microscopic systems is generally described by non linear laws. (The non-linear laws may explain irreversible phenomena like instabilities, dualism, unevolving societies, cycles of growth and decay of societies. The linear laws are only linear approximation of the non-linear laws at a point in time and space.)"    -  Ilya Prigogine, Nobel Laureate



In this book,  there are 29 chapters in total, I think it would be a length post to write all of the quotes in one post, let me know if you want the others. If you want to buy the book, go to the Amazon link I have given above. 

Thanks.

Rock Quality Designation (RQD)

Rock Quality Designation  was introduced by D.U. Deere (1964) (Practical Approach to Civil Engineering by Singh and Goel) as an index of assessing rock quality quantitatively. RQD is a modified per cent core recovery which incorporated only sound rock core pieces that are 100 mm or greater in length along the core axis.

RQD  = (Sum of core pieces >= 10 cm)/ total drill length *100

Following are the methods of obtaining RQD :

a. Direct Method

International Society for Rock Mechanics(ISRM) recommends a core size of at least NX (size 54.7 mm) drilled with double-tube core barrel using a diamond bit. All the artificial fractures should be ignored while calculating the core length for RQD.
The relationship between RQD and engineering quality of the rock mass as proposed by Deere in 1968 is given as below:

S.No.          RQD (%)           Rock Quality
 1.                 <25                      Very Poor
 2.                 25-50                   Poor
 3.                 50-75                   Fair
 4.                 75- 90                  Good
 5.                 90- 100              Excellent

RQD determination - Direct Method ( Photo credit- A Practical Approach to Civil Engineering by Singh and Goel)

b. Indirect Method:
1. Seismic Method : The seismic survey method makes use of the elastic properties of strata that affect the velocity of the seismic waves travelling through them. This method is cheap, rapid and relatively easy to apply. We can find out the following information from this method:
a) Location and configuration of bed rock and geological structures in the subsurface.
b) The effect of discontinuities in rock mass may be estimated by comparing the in-situ compressional wave velocity with laboratory sonic wave velocity of intact drill core obtained from the same rock mass.
                RQD(5) = (Vi/Vl)^2 * 100
Where, Vi is the in-situ compressional wave velocity and Vl is compressional wave velocity in the intact rock core.

2. Volumetric Joint Count Method:
The RQD can be determined by counting the number of joints(discontinuities) per unit volume Jv.  A simple relationship(given by Palmstrom, 1982), RQD = 115 - 3.3*Jv , can be used to convert Jv into RQD for clay free rock masses.

Here Jv is the number of joints per cubic meter of the rock mass.
There are few other methods, which I shall cover up in the upcoming posts.

Thank You!

Helical Auger boring and determination of water content and specific gravity

Theory:
Helical Augers are used to get the disturbed soil samples from the surface or near to the soil surface. The size of augers varies from 75mm to 200mm. These samples can be used to determine the nearest ground water level, or to determine the water content at various depths. Generally hand augers are used up to the depths of 6m but they can be used up to 30 m depths. Other properties such as particle size distribution and specific gravity can also be determined using these disturbed samples.

Hand Augers (Image source: www.bestengineeringprojects.com)

Apparatus/Equipment:

• Helical Auger bore with the handle
• Scale and sample collectors.
• Other apparatus for the water content determination and specific gravity determination, such as the oven, soil cans and pycnometer.

Procedure:

1. Fix the T-handle correctly to the Auger.
2. Press the auger into the ground and rotate the auger clockwise to get it sink into the ground to the required depth in the area under investigation.
3. When the annular space between the blades is filled with the soil, it is withdrawn and cleaned.
4. The cleaned auger is again inserted and the process is repeated.
5. Extension rods are attached when bore hole progresses downwards.
6. Take the samples from the various depths and then various tests are performed to check their properties.

Precautions:

1. The auger is rotated and pressed at uniform rate.
2. Clean the blades of the auger after the experiment is over.
3. Joining of the extension rods should be done carefully.
4. The sample should be collected at every 30cm boring and sample should be extracted whenever the strata is changed.
5. Straight driving should be done.

Limitations:

1. Helical Auger does not work in rocky strata.
2. Sample cannot be obtained under water.

Introduction to Dynamic Soil Properties

Hi, How have you been?

Soil dynamics is the study of the behavior of the soil under the dynamic loads. When the loads are larger such as the earthquake loads, Blasts or the nuclear explosions, the strain rate of the soil is from 0.01% to 0.1%, while the strain rate in the soil is comparably low of order 0.0001% to 0.001 % in case of the small loading such as the loading on the foundation of the reciprocating machines.

In order to analyse and design the structures subjected dynamic loading, we have to study the following dynamic properties of the soil:

1. Dynamic moduli, such as Young's modulus of Elasticity 'E', Shear modulus 'G', and bulk modulus 'K'.
2. Poisson's ratio
3. Dynamic Elastic constants, such as the co-efficient of uniform compression 'Cu'; Co-efficient of uniform Shear 'Ct', co-efficient of non uniform compression and Co-efficient of non-uniform shear. 
4. Damping Ratio
5. Liquefaction parameters, such as the cyclic stress ratio, cyclic deformation and pore water pressure response.

Dynamic properties of the soil are dependent upon the strain, and several laboratory and field techniques been developed to measure these properties over a wide range of strain amplitude.

Resonant column test, Ultrasonic Pulse test, Cyclic simple shear test, Cyclic torsional simple shear test, and cyclic tri-axial compression tests are the type of the laboratory tests used to determine the dynamic soil properties.

Thank you :)

Vertical Piles of a Group subjected to Eccentric Loading.

Greetings!

In order to determine the load distribution  between the vertical piles of a group subjected to eccentric loading, we have to consider the two cases of loading:

(a) When eccentricity is about one axis only

Vpi =  V/n  +-  (V.e.Xi.A)/Ig

Where,  Vpi = Load on the ith pile

              V = Total vertical load acting on the pile group.

Accentric loading on pile group

             n = Total no. of piles.

             e= amount of eccentricity w.r.t. the centre of the pile group. 

             Xi = Distance of the centre of the ith pile from the centre of the pile group, measured parallel to e. 

             Ig = Moment of Inertia of the piles about the axis normal to the direction of eccentricity. 

                 = A.X1^2 + A.X2^2 +.... + A.Xn^2

             A = Area of the pile cross-section and 

           X1, X2, ...... Xn = Distance from centre of gravity of pile group to the line of each pile, measured parallel to e. 

Since, all the piles in the group are assumed to be identical, above equation can be written as:

Vpi =  V/n  +-  (V.e.Xi.)/Sum(Xi.^2).

(b) When eccentricity is about two axes:

When there is eccentricity about both the axes, individual pile loads may be determined by the method of superposition:

Vpi =  V/n  +-  (V.ey.Yi.A)/Ix   +-  (V.ex.Xi.A)/Iy

where, V, n and A have the same meaning. 

  

Eccentric loading on pile group

ex = Amount of eccentricity w.r.t. centre of pile group measured along x-axis.

ey = Amount of eccentricity w.r.t. centre of pile group measured along y-axis.

Ix = Moment of inertia of the piles about x-axis. == A.Y1^2 + A.Y2^2 +.... + A.Yn^2

Iy = Moment of inertia of the piles about the y-axis = = A.X1^2 + A.X2^2 +.... + A.Xn^2

Xi = distance from the centre of gravity of the pile group to the line of each pile, measured parallel to the x-axis, and 

Yi = distance from the centre of gravity of the pile group to the line of each pile, measured parallel to the y-axis.

Reference: Analysis and Design of Sub-Structures by Swami Saran

Thank you :)

Underground Excavation problems

Greetings!
This post contains the brief lecture notes on the topic "Underground Excavation problems".

There are three types of underground excavation problems, which we come across in general:

1. Stability of excavation
2. Dewatering
3. Effect on the adjoining structures

In my previous post, I discussed the first part of this topic, i.e. Stability of Excavation. In this post, I will take up the second part, i.e. Dewatering.

Dewatering:

Dewatering is required for deep construction excavations, such as power houses, pumping stations, bridge foundations and so on. Practically any foundation below water table will require dewatering, however, if the soil has got low permeability i.e. less the 10^(-6) cm/sec, much problem due to seepage of water is not posed, because the discharge is small. 

However, if the discharge  is more, that is case of permeable soils having permeability more than 10^(-5) cm/sec, dewatering is essentially required. Extent of dewatering will depend upon characteristics of soil, presence of water bearing stratas, aquifer parameters and the field permeability.

 The dewatering job is to estimate the rate seepage of water, for this a central circular well is constructed, and the rate of discharge is estimated for a fully penetrating well. 

The rate of discharge will depend upon the geometry and extent of excavation and the desired level of lowered ground water table. 

A no. of wells are placed around the periphery of excavation and the water is pumped out simultaneously out of the wells.

There are three methods of dewatering:

1. Sump Pumping
2. Deep well pumping
3. well point dewatering.

Sump Pumping: If the soil is cohesive, having low permeability, shallow trenches are dug along outer edges of the excavation to collect water and to pump it out through the pumps. It is particularly suitable in clayey and silty clay, where the rate of seepage is low.

This method is inexpensive and easy to operate. The greatest depth upto which this method can be adopted is 5 to 6 m below the pump level.

Deep Well Pumping: Deeps wells are installed along the sides of excavation and water is continuously pumped out. This method is suitable for highly permeable soils such as sand and silty sand. A group of wells is installed, then the effect of pumping is observed, if sufficient control is not achieved, additional wells or pumps may be added. 

Deep wells must be constructed in such a way that they remove the large quantity of water, without allowing the silt to enter into the well casing.

Well Point Pumping: It consist of installation of nos. of well points around usually excavation. The vertical raiser pipes are connected to the header main on ground. The water is drawn into the riser pipe and discharged by the header pipe. The distance between the well points is 1 to 1.5 m. 

Thanks!

Consolidation Test (IS 2720- part 15 - 1986 )

AIM: This test is performed to determine the consolidation properties of a given soil as listed below:

1. Co-efficient of compressibility
2. Co-efficient of volume change
3. Co-efficient of consolidation Cv
4. Compression Index
5. Pre-consolidation Pressure, Cc
6. Co-efficient of permeability, K

STANDARD REFERENCE: IS: 2720(part 15) - 1986 - Determination of consolidation properties.

THEORY: Consolidation is the process of removal of pore water present in the soil gradually due to the application of sustained static load. Because of consolidation, there will be decrease in volume of soil mass.

SIGNIFICANCE: The consolidation data of soil is used to predict the rate and amount of settlement of structure founded on clay primarily due to volume change. In addition, the following information can be obtained for foundations resting on clay using consolidation data.

1. Total settlement of foundation under any given load.
2. Time required for total settlement due to primary consolidation.
3. Settlement for any given time and load.
4. Time required for any percent of total settlement or consolidation.
5. Pressure due to which soil already has been consolidation or compressed.

APPARATUS REQUIRED: 

1. Consolidometer
2. Loading device (Jack or lever system)
3. Ring of non-corrosive material
4. Porous stone
5. Water reservoir
6. Soil trimming tool like wire saw, knife or spatula etc.
7. Balance (0.01 gm sensitivity)
8. Dial gauge (0.01 mm accuracy)
9. Oven
10. Desiccators
11. moisture content cans
12. Stopwatch.
13. Scale ( 0.5 mm least count)

PROCEDURE: 

1. Clean the ring and weigh it empty.
2. Measure the height and diameter of the consolidation ring.
3. For undisturbed soil specimen, insert the ring in the soil mass by pressing with hand and remove the material around the ring.  The soil specimen so cut should project about one centimeter on either side of the ring.
4. Trim the specimen to flush it with the top and bottom of the ring.
5. Remove any soil sticking outside of the ring and weight the ring with the soil specimen.
6. For remoulded specimen, compact the soil in the ring to the desired density and weigh it.
7. Determine the moisture content of the extra soil removed from outside the ring.
8. Assemble the consolidometer with the ring having the soil specimen and saturated porous stones on top and bottom of the specimen. Place the filter paper between the soil specimen and the porous stone.
9. Mount the assembly on the loading frame and the dial gauge is set in position in such a way that the dial is at the beginning of its release run.
10. Connect the system to a reservoir with the same level as that of specimen. Allow the water to flow into the sample till its saturation is achieved.
11. After saturation, note initial reading of the dial gauge.
12. Apply the normal load to give the desired pressure intensity of 2.5 N/cm^2 on the soil specimen. 
13. Not the dial gauge reading at elapsed times of o, 0.25, 1.0, 2.25, 4, 9, 16, 25, 36, 49, 64, 81, 100, 169, 256, 361, 600, 1440 - minutes from the instant of  application of load. The dial gauge readings are taken until 90% consolidation is reached or atleast for 24 hours.
14. Increase the normal load to give the doubled pressure intensity of the previous pressure or 5 kN/cm^2.
15. On successive days, apply the loads to give the pressure of 10, 20, 40 and 80 N/cm^2 for the desired pressure intensity.
16. After the last load is applied, decrease the load 1/4 th the value of the last laod i.e. 20 N/cm^2 and allow to stand for 24 hours.
17. Note the dial gauge reading after 24 hours.
18. Further reduce the load in steps of 1/4th the previous load and repeat the observations.
19. If data for repeated loading is required, the load intensity is increased and observations are repeated.
20. Finally reduce the load to the initial setting load, keep for 24 hours and final dial gauge reading is recorded.
21. Dismantle the consolidation ring and weigh it after gently removing any surface water present.
22. Dry the specimen in the oven for 24 hours and weigh the dry soil specimen.
23. Draw graphs between:

               (a) Dial gauge reading versus under root of time on normal graph sheet and determine t90 for all the pressure by square root of time fitting method.

               (b) Dial gauge reading versus root of time on semi log graph sheet and determine t50 for all pressure by logarithm of time fitting method.

               (c) Void ratio 'e' versus pressure curve.

               (d) Void ratio 'e' versus load of pressure on semi-log graph sheet.

Square root time fitting method

RESULTS AND COMMENTS: 

Average value of the co-efficient of compressibility =

Average value of co-efficient of consolidation, Cv = 

Average value of co-efficient of volume compressibility =

Average value of co-efficient of permeability, K = 

Compression Index, Cc =