1129215843isrm_sm_in_situ_deformability_-_1979

Prévia do material em texto

In Situ Deformability of Rock 197 
Suggested Methods for Determining In Situ 
Deformability of Rock 
PART 1. SUGGESTED METHOD 
FOR DEFORMABILITY 
DETERMINATION USING 
A PLATE TEST 
(SUPERFICIAL LOADING) 
SCOPE 
1. (a) The plate test which uses surficial loading, often 
referred to as the uniaxial jacking test or plate jacking 
test, is performed in small tunnels or test adits to 
measure the deformation characteristics of a rock mass. 
(b) Two areas, each approximately 1 m in diameter, 
are loaded simultaneously using jacks positioned across 
the tunnel. Rock mass deformations are measured in 
boreholes behind each loaded area and across the tun- 
nel between each loaded area. A typical test facility 
is shown in Fig. 1. 
(c) Incremental and cyclic loading provide data for 
the calculation of elastic, deformation, and unloading 
moduli. The creep characteristics of the rock mass can 
be determined from graphs of displacement versus time. 
PARTICLE BOARD 
TOP PL 
TUNNEL ROCK 4 RESTRAINT 
BASE PLATE--~ GAGE 
(d) The effects of anisotropy can be determined by 
orienting the thrust of the jacks in any desired direc- 
tion. However, it is advisable that the thrust of the 
jacks remains in a plane perpendicular to the axis of 
the test tunnel. 
EQUIPMENT 
2. (a) Equipment necessary for accomplishing the test 
includes items for: preparing the test site, drilling and 
logging the instrumentation hole, measuring the rock 
deformation, applying and restraining test loads, 
recording test data, and transporting various com- 
ponents to the test site. 
3. (a) Test site preparation equipment should include 
an assortment of excavation tools, such as drills and 
chipping hammers. Blasting should not be allowed dur- 
ing final preparation of the test site. 
4. (a) The drill for the instrumentation holes should, 
if possible, have the capability of retrieving core from 
depths of at least 10 m. Some type of borehole viewing 
device is desirable for examination of the instrumen- 
tation holes to compare and verify geologic features 
observed in the core. 
:LAT JACK, APPROX. 
I M DIAMETER 
*CONCRETE / 
/ "-'-MPBX MEASURING ANCHORS 
(5 OR MORE PER HOLE) 
MPBX SENSOR HEAD 
~UBBER SLEEVE OVER 
LEAD WIRES 
NX, 76 MM DIAMETER, 
CORE DRILL HOLE 
APPROX. 6 FLATJACK 
DIAMETERS D E E P ~ 
/ HYDRAULIC 
SCREWS FOR SET 
UP AND REMOVAL 
LEAD WIRE 
PREPARED DIAMETER 
1.5 TO 2 TIMES 
FLATJACK DIAMETEI 
DATA ACQUISITION STEM ----~ 0 @ ® 0 ® 
Fig. 1. Uniaxial jacking test. 
MPa HYDRAULIC PUMP 
~ NOTE: TtMBER PLATFORM 
FOR SUPPORT DURING 
ERECTION NOT SHOWN 
198 International Society for Rock Mechanics 
(b) Instruments for measuring deformations should 
include a reliable multiple position borehole exten- 
someter (MPBX) for each instrumentation hole, and 
a tunnel diameter gauge. All instruments should be of 
sufficient accuracyand sensitivity to be compatible with 
anticipated deformations. Experimental errors in excess 
of 0.01 mm can invalidate test results when the modulus 
of the rock mass exceeds 3.5 x 104 MPa. A discussion 
of the ramifications of experimental error can be found 
in [1]. 
5. (a) The loading apparatus should be capable of 
applying simultaneous uniform pressures to two areas 
on opposite sides of the tunnel, each approximately 1 m 
in diameter. As shown in Fig. 1, the equipment used 
to apply the desired loads to the prepared and instru- 
mented rock may consist of calibrated flat jacks and 
restraint columns having the capability of sustaining 
the maximum desired uniform pressure with a suitable 
factor of safety. The hydraulic pump system with 
necessary fittings, valves, gages, and hoses should have 
sufficient pressure capability and volume to apply and 
maintain desired pressures to within 3?/0 of a selected 
value throughout the duration of the test. 
PROCEDURE 
6. Site preparation 
(a) The area selected for testing should be carefully 
prepared. All loose rock material should be removed 
by using chipping hammers and drills. In order to 
reduce the restraining influence of adjoining rock, an 
area with a diameter 1½ to 2 times that of the test 
pad should be prepared. The two test areas should be 
concentric with and in planes oriented perpen- 
dicular to the axis of the restraint column assembly. 
If blasting is required for initial test surface prep- 
aration, care should be exercised to produce surfaces 
which are relatively free from blast damage. Detailed 
site preparation procedures can be found in [2]. 
(b) An instrumentation hole should be core drilled 
into each prepared test surface. Care must be exercised 
to insure that the two holes are coaxial with each other 
and with the restraint column assembly. 
(c) Examination of the core and the instrumentation 
hole itself will assist in locating anchor points for the 
MPBX's. The anchors should be located so that they 
are not placed on joints, and so they bracket zones 
of structural or lithologic change. The deepest anchor 
should be located approximately 6 flat jack diameters 
below the rock surface in order to provide a fixed point 
to which the movements of all other anchors can be 
referenced. In general, the remaining anchors should 
be concentrated in the zone of maximum stress between 
the rock surface and a point approximately 3 jack dia- 
meters back from the surface. Figure 2 illustrates some 
recommended locations. It is desirable for the sensor 
head and all anchors to be attached to the side walls 
of the instrumentation hole. This precludes the neces- 
sity of monitoring the movement of the test setup com- 
ponents, since all measurements will be referenced in 
the rock. 
7. Equipment installation 
(a) The complete installation of a proposed type of 
restraining and load applying setup together with 
deformation measuring instrumentation is shown sche- 
matically in Fig. 1. A properly located wooden platform 
(not shown in Fig. I) allows for alignment of all test 
components. The space between the flat jack assembly 
and rock should be filled with small aggregate concrete. 
,=., 
F, 
r~ 
.1 ROCK SURFACE 
~ SENSOR H E ~ ~'~ 
OPEN JOINTS " ~ ~ 
NO STRUCTURAL 
OR LITHOLOGIC 
FEATURES 
JOINTS 
I 
iii.! ..... 
I I 
LITHOLOGY 
CHANGE 
NOTE: NOT TO SCALE 
~ - - ~ v ~ l l l l l l r ~ 7 ~ 
;OUGE 
SEAM 
O D ~ 
3 D ~ 
6 D - - 
SCALE 
D= Jack D i a m e t e r 
Fig. 2. Typical anchor locations. 
In Situ Deformability of Rock 199 
The concrete should be allowed to cure sufficiently to 
obtain adequate strength prior to commencement of 
the test. The space between the fiat jack and the base 
and top plates should have a special partical board 
filler (wood chips and resin) or other suitable material 
fabricated to accommodate the flat jack configuration 
on one side and the base plate on the other side. 
8. Testing 
(a) After all components of the instrumentation are 
installed in the drill holes, they should be checked (elec- 
tronically or mechanically). After the loading and re- 
straining components are installed, another check 
should be made of the instrumentation. A final check 
of all mechanical, hydraulic, and electronic components 
should be made after the concrete pads are placed and 
again before the first load increment is applied. 
(b) Tests should be conducted continually on a 24-hr 
a day basis utilizing load ranges and increments com- 
patible with the particular design considerations under 
investigation. 
(c) While the test is in progress, rock deformations 
monitored by the instrumentation should be recorded 
continuously or at sufficient intervals to obtain desired 
data. If a noncontinuous recording system is utilized, 
a minimum of four readings during the first hour of 
each load increment or decrement is recommended. 
(d) The maximum test pressure, number of cycles to 
the maximum pressure, and number of pressure incre- 
ments in each cycle will be determined by test con- 
ditions and desired information. A maximum pressure 
of 1.2-1.5 timesthat imposed by the structure is usually 
considered adequate. At least five pressure increments, 
each followed by a period of zero pressure, should be 
used for each cycle. A typical one-cycle loading 
sequence is shown in Fig. 3. 
(e) The duration of each pressure increment will be 
determined by the creep characteristics of the rock 
mass. Until the behavior of the rock mass is well under- 
stood, at least 48 hr should be allowed for each pressure 
increment followed by 24 hr at zero pressure. Obser- 
vations during the first pressure increments can be used 
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D E F O R M A T I O N , MM 
Fig. 3. Rock Surface deformation as a funct ion of bearing pressure. 
200 Internat ional Society for Rock Mechanics 
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In Situ Deformability of Rock 201 
to modify time requirements for successive increments. 
Jack pressure should be maintained within 3% of the 
target value for the duration of each increment. The 
time frame for a typical test is shown in Fig. 4. 
CALCULATIONS 
9. (a) Data gathered during the test may be plotted to 
provide a display of Deformation vs Time, Pressure, 
or Depth. These plots aid in the analysis of the creep, 
rebound, and permanent set characteristics of the rock 
mass. Example plots are shown in Figs 3, 4, and 5. 
(b) Deformation measurements for the various load 
cycles are utilized to compute deformation moduli 
according to appropriate formulae. Because of their 
simplicity, expressions based on the theory of elasticity 
I-3] are normally used to approximate actual field con- 
ditions. 
(c) For a uniformly distributed pressure on a circular 
area, the displacement at any point beneath the center 
of the area may be expressed: 
2q(1 -/~2) 1-( a2 + z2) 1/2 _ z] 
w=- E 
qz(1 + #)[z(a 2 + z2)_1/2 _ 1] (1) 
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0.6 
0.9 
1.2 
1.5 
1.8 
2.1 
2.4 
2.7 
5.0 
3.4 
3.7 
4.0 
4.3 
4.6 
4.9 
f 
ROCK DISPLACEMENT ( M M ) 
0.102 0.203 O. 305 0.406 O. 508 0.610 
A N C H O R DEPTHS 
SENSOR HEAD 0 .0 M 
ANCHOR ONE 0 .5 M 
ANCHOR TWO I. I M 
ANCHOR THREE 1.8 M 
ANCHOR FOUR 2.4 M 
ANCHOR FIVE 3 . 2 M 
ANCHOR SIX 4 . 3 M 
ANCHOR SEVEN 6. I M 
O-DEPTHS WHERE 
ROCK DEFORMATION 
WAS MEASURED 
WHEN LOADS WERE 
APPLI ED AT SURFACE 
( 0 - DEPTH ) 
5.2 
5.5 
561 I 
I / D E E P E S T EXTENSOMETER ANCHOR 
6 j d r I ~ I 
I 
Fig. 5. Uniaxia l displacement vs depth referenced to deepest anchor at 6.9 M P a bearing pressure. 
202 International Society for Rock Mechanics 
where: 
wz = displacement in the direction of the applied 
pressure 
z = distance from the loaded surface to the 
point where displacement is calculated 
q = pressure 
a = radius of loaded area 
/2 = Poisson's ratio 
E = modulus of elasticity 
At the surface z = 0 and the expression reduces to: 
2(1 - / 2 2) 
wz = o - - qa . (2) 
E 
(d) When loads are applied with a circular flat jack 
with a hole in the center, the effect of the unloaded 
area in the center must be subtracted. Using the 
notat ion: 
a 2 : outer radius of flat jack 
al = inner radius of flat jack or radius of hole 
_ 2 q ( 1 - 2) 
Wz /2 [(a 2 + z2) l /E(a2 + z2) 1/2] 
E 
z2q( 1 + /2) Z2)- 1/2 + [(a 2 + _ (a 2 + z2) - 1/2]. (3) 
E 
After substituting appropriate values for al, a2,/2, and 
Z, equation (3) reduces to: 
= E ( K z ) . (4) Wz 
If displacements Wzl and Wz2 are measured at points 
z I and z 2, the indicated deformation modt~lus of the 
material between zl and Zz may be calculated from: 
Ea = q W~, W~2 ]" (5) 
R E P O R T I N G OF RESULTS 
10. The report should include the following: 
(a) A complete geologic description of the test site in- 
cluding core logs, photos of core, photos of prepared 
test areas, and a description of local blast damage. 
(b) A description of the testing apparatus including 
photos of installed equipment, a schematic diagram of 
the equipment, specifications for accuracy and sensi- 
tivity of all pressure and deformation instruments, and 
calibration data for all instruments. 
(c) Tabulations of unreduced data. 
(d) Plots of deformation versus pressure such as in 
Fig. 3. Information from this plot can be used to deter- 
mine the shape of the stress strain curve, to obtain 
values for calculation of various moduli, and to deter- 
mine rebound and elasticity characteristics. 
(e) Plots of deformation versus time as in Fig. 4. This 
plot is useful for studying the creep characteristics of 
the rock. It should be kept during testing to establish 
time requirements for each load increment. 
(f) Plots of deformation versus depth referenced to 
the deepest anchor as in Fig. 5. This deformation pro- 
file is used to identify anomalous areas with lower or 
higher moduli than the average. Once such zones are 
identified, they can be correlated with core from the 
instrument holes. If MPBX anchors are located pro- 
perly, the moduli of these zones can be calculated using 
equation (5). 
(g) Calculated moduli pertinent to design problems. 
Care should be taken to identify the depth interval in 
the rock mass and stress range for each modulus. 
R E F E R E N C E S 
1. Benson R. P., Murphy D. K. & McCreath D. R. Modulus testing 
of rock at the churchill falls underground powerhouse, Labrador, 
from determination of the in situ modulus of deformation of rock, 
American Society for Testing and Materials STP477, (1969). 
2. Misterek D. L., Slebir E. J. & Montgomery J. S. Bureau of recla- 
mation procedures for conducting uniaxial jacking tests, paper 
presented at American Society for Testing and Materials Annual 
Meeting, June 24-29, 1973, Philadelphia, Pennsylvania. 
3. Timoshenko S. & Goodier J. N. Theory of Elasticity. McGraw- 
Hill, New York (1951). 
PART 2. SUGGESTED 
METHOD FOR FIELD 
DEFORMABILITY 
DETERMINATION USING 
A PLATE TEST 
D O W N A BOREHOLE 
SCOPE 
1. (a) This test is used to determine the in s i t u deform- 
ability characteristics of a rock mass. Successively higher 
bearing pressures, in loading and unloading cycles, are 
applied to the flattened end of a borehole and the 
resulting rock displacements are recorded. 
(b) Elastic and deformation modulae may be derived 
from graphs of bearing pressure versus displacement. 
Time dependent (creep) properties may be determined 
from graphs of displacement versus time. 
(c) The method allows the testing of several horizons 
at various depths, with a minimum of expense to gain 
access to each test horizon. In the limit a semi-con- 
tinous log of deformability as a function of depth can 
be obtained. 
(d) The direction of loading necessarily coincides 
with the borehole axis, usually near-vertical, so that 
no information can be obtained regarding rock aniso- 
tropy. The size of the loaded area is limited by the 
capabilities of available drilling equipment and is 
usually smaller than in other plate tests (see PART 1). 
(e) The method is usually employed to provide infor- 
mation for the design of foundations, as an alternative 
to the method of PART 1 where access to the proposed 
foundation level cannot readily by obtained by an ex- 
ploratory trench or addit. 
In Situ Deformability of Rock 203 
APPARATUS (e.g. Figs 1 and 2) 
2. Equipment for drilling, cleaning and preparing the 
test hole including: 
(a) A drill or boring machine to produce a test hole 
of diameter at least 500 mm 1. to the maximum depth 
of investigation. 
(b) Casing as necessary to stabilize the walls of the 
hole. 
(c) Groundwater lowering or other equipment to 
allow preparation ofthe bearing surface and instal- 
lation of the bearing plate in dry conditions. 
(d) A bottom auger, reaming bit or hand tools to 
prepare the bearing surface flat (+ 5 mm) and perpen- 
dicular to the hole axis (+3°). 
(e) Equipment to remove debris from the hole. 
(f) Equipment for taking core samples to a depth 
of at least 3 m below the bearing surface, the diameter 
of the exploratory hole to be less than 109/o that of 
the bearing plate. 
3. Equipment for installing and bedding-in the bearing 
plate including: 
(a) equipment for lowering the plate into the test hole 
(b) materials and ancilliary equipment for preparing 
a bedding layer beneath the plate, for example of 
cement mortar and plaster of paris. 
4. A circular bearing plate of diameter at least 500 mm 
and sufficiently rigid to distort by not more than 1 mm 
under the test conditions. 2 
5. A loading column to transmit the applied force from 
the reaction system to the test plate, such that: 
(a) it resists buckling and carries the applied load 
without distortion sufficient to affect test results 
(b) it is hollow to take the measuring column. 
(c) the resultant load acts centrally to the bearing 
plate (+3 mm) throughout the test. 
6. A loading and reaction system including for example 
a. hydraulic jack, reaction piles or anchors and ancillary 
equipment, such tha t 
(a) load is applied axial to the loading column. 
(b) loads can be varied throughout the required range 
and can be held constant to within 2~o of a selected 
value for a period of at least 24 hr. 
(c) the travel of the loading jack should be greater 
than the sum of anticipated displacements of the test 
plate and reaction beam. 
(d) the reaction system should be of appropriate 
materials, design and construction to satisfy these re- 
quirements and to ensure safe operation of the test 
equipment. 
(e) reaction anchors should if used be located further 
than l0 test hole diameters from the bearing plate. 
7. Load measuring equipment, for example a load 
cell or proving ring, to measure the applied load with 
an accuracy better than __+ 2 ~ of the maximum reached 
in the test. 
8. Equipment to measure displacement of the centre 
of the bearing plate 3 in a direction axial to the test 
* N u m b e r s refer to N O T E S a t t he e n d o f the text. 
hole, such that: 
(a) The system should have a range greater than the 
maximum plate displacement in the test, and an overall 
accuracy better than + 0.05 mm. 
(b) The system reference beams, columns and clamps 
should when assembled be sufficiently rigid to meet this 
requirement. 
(c) The reference anchors for displacement measure- 
ments should be rigidly installed at a distance greater 
than 10 test hole diameters from the loading plate and 
reaction anchors. 
9. A timing device to measure test durations of up to 
48 hr, reading to l see. 
P R O C E D U R E 
10. Test site selection 
(a) The test site is selected to allow testing at the 
actual foundation level with loading in the direction 
of foundation loading, alternatively testing of rock con- 
sidered typical of anticipated conditions. 
(b) Attention should be given not only to the test 
hole location, but also to suitable locations for reaction 
and reference anchors, to groundwater and other con- 
ditions that may influence the conduct of the test. 
(c) Selection of horizons for loading should be 
checked before the test starts, by examining in detail 
a core taken from beneath the proposed bearing sur- 
face. 
11. Drilling and preparation 
(a) Test hole and anchor locations are accurately 
marked out and the holes drilled to the required elev- 
ations. The test hole is cased as necessary to ensure 
stability throughout the test. Exploratory core is taken 
to a depth of at least 3 m below the proposed test hor- 
izon, and the choice of horizon confirmed or modified. 
Detailed geotechnical logs of all boreholes should be 
prepared by examining core and/or the walls of the 
hole. 
(b) When groundwater is encountered in the test 
hole, steps should be taken to lower the water table 
(for example by pumping from well points surrounding 
the test area) for long enough to allow installation of 
the bearing plate. 
(c) The bearing surface is trimmed flat (___ 5 ram), and 
its elevation recorded. All debris should be removed.* 
One or more layers of mortar or plaster scree, total 
thickness less than 30 mm, are placed to cover the bear- 
ing surface and the bearing plate installed before the 
last layer of scree has set. The delay between excavation 
of the bearing surface and installation of the equipment 
should not exceed 12 hr. 5 
(d) Reaction and reference anchors are installed and 
the equipment assembled and checked. A small seating 
load (approximately 5~ of the maximum test value) 
is applied and held until the start of testing. 
(e) The water table should be allowing to return to 
its normal elevation before the start of testing. 
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In Situ Deformability of Rock 205 
Jack 
Dial 
i 
-I To reference 
beam 
Loading column 
Measuring 
column support 
Measuring 
Fig. 2. Details of plate-test equipment. 
ht liner 
......" ~ P l a s t e r of Paris 
;ement mortar 
12. Testing 
(a) With the seating load applied (paragraph lid), 
load and displacement should be observed and 
recorded over a period not less than 48 hours to estab- 
lish datum values and to assess variations due to 
ambient conditions. 6 
(b) Loads and load increments to be applied during 
the test should be selected to cover a range 0.3-1.5 qo, 
where qo is the stress intensity produced by the pro- 
posed structure, v 
(c) Load is increased in not less than five approxi- 
mately equal increments to a maximum of approxi- 
mately 1/3 the maximum for the test. At each increment 
the load is held constant (___3~) and displacement 
recorded as a function of time until it stabilizes. 7 The 
procedure is continued for decreasing load increments 
until the seating load is again reached. 
(d) The procedure 12(c) is repeated for maximum 
cycle loads of approximately 2/3 and 3/3 the maximum 
for the test. 
13. The equipment is removed from the test hole and 
further tests may be carried out on deeper horizons 
by re-drilling in the same hole (paragraphs 11 and 12). 
CALCULATIONS 
14. (a) Graphs are plotted of incremental settlement 
(or uplift in the case of unloading) against the logarithm 
of time (Fig. 3). 
(b) Bearing pressure versus settlement curves are 
plotted for each test (Figs 4 and 5). 
(c) Deformation modulae may be determined from 
tangents to the pressure-settlement curve. In Fig. 6 
three such moduli are defined where 
and 
Ei is the initial tangent modulus 
E e is the elastic modulus obtained from a re- 
loading cycle 
Ey is a "yield" modulus. 
206 
Qli 
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i 
International Society for Rock Mechanics 
• '" 451 k P a 
~ 71~ kPa 
-~__1180 k P a 
I I I 
10 100 1000 
Time (minutes) 
Fig. 3. Typical relationships between incremental displacement and time for various load-intensities. 
(d) The modulus is calculated from the formula 
dq ~ D ( 1 - v 2) I~ E = 
where 
q is the applied pressure 
p is the settlement 
D is the plate diameter 
v is Poissons's ratio (between 0.1ar/d 0.3 for 
most rocks) 
lc is a depth correction factor given in Fig. 7. 
(e) A time-dependent parameter R (known as the 
creep ratio) is determined for each load increment. The 
parameter R is defined as the incremental settlement 
per cycle of log time divided by the total overall settle- 
ment due to the applied pressure. The relationship 
between R and applied pressure may be presented 
graphically (Fig. 8). 
REPORTING OF RESULTS 
15. The report should include the following 
(a) Diagrams and detailed descriptions of the test 
equipment and methods used for drilling, preparation 
and testing. 
(b) Plans and sections showing the location of tests 
in relation to the generalized topography, geology and 
groundwater regime. 
(c) Detailed geotechnical logs and descriptions of 
rock at least 3 m above and below each tested horizon. 
(d) Tabulated test results, graphs o f displacement 
versus time for each load increment, and graphs of load 
versus displacement for the test as a whole (e.g. 
Fig. 4). 
(e) Derived values of deformability parameters, 
together with details of methods and assumptions used 
in their derivation. Variations with depth in the ground 
should also be shown graphically as 'deformability pro- 
files' superimposed on the geotechnical log of the test 
hole. 
NOTES 
1. The test hole should preferably be of sufficient 
diameter to allow manual inspection, and preparation 
of the bearing surface. Where the hole is insufficiently 
0. 
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Fig. 4. Typical plate-test results for Grade II chalk. 
In Situ Deformability of Rock 207 
0 
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Load intensity (k Pa ) 
2 0 0 4 0 0 6 0 0 8 0 0 I 0 0 0 1200 
E 
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Fig. 5. 
large for manual inspection it must be core-drilled to 
provide adequate samples for a detailed geotechnical 
log of ground conditions. 
2. The bearing plate, if of steel unreinforced by webs, 
should be at least 20mm thick for a diameter of 
500 mm. 
3. If required, the displacement of rock at any level 
below the bearing plate may be monitored, using rods 
passing through a hole in the centre of the plate and 
rigidly anchored in the exploratory drillhole. 
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E ® 
~o.52 
i~=0.49 
~ ~ _ =, 0.25 case la) 
s,--O.O 
I 
- I 
1 
I 
% 
i~:0.5 
~ ' " " I ""l ,,,,.4f._ "1 . . . . i-case (bl 
5 tO 15 20 
• - Z / D 
o _,.IDI., - ~ I 
Fig. 7. (a) Uniform circular load at base of unlined shaft. (b) Uniform 
circular load within semi-infinite solid (case treated by Fox, 1948). 
4. When the test hole is large enough, rock trimming 
and installation of the bearing plate should be carried 
out by hand. When this is not possible, cleaning may 
be carried out with an auger or similar device operating 
at the end of a drill rod assembly, and the mortar scree 
placed using a tremie or bottom opening bucket. 
5. Particularly when testing weaker rocks there'will 
be rebound, loosening and possibly swelling associated 
with excavation of the bearing surface and changes in 
groundwater conditions. This may be minimized by 
reducing the delay between excavation and testing to 
a minimum. 
6. Small fluctuations in displacement are likely to 
result from changes in the groundwater regime, tem- 
perature and other environmental effects. 
7. At higher applied loads the displacement may not 
completely stabilize in a rcasonab!c ',imc: a criterion 
150( 
0 
n 
, - I00( 
.m 
m =.. 
5o¢ 
"10 
g 
. J 
I & 
I~l o T4.1 
+ ; i T 4 . 2 
~l x x T4.3 
+ T2.1 
+ X~ A A T2 .3 
t 
X ~ 0 A 
+ I 
I I I I ! 
0 ~0 20 30 40 50 6b 
R(per cent) 
Fig.8. Relationship bctween load-intensity and creep ratio R fromplate 
Fig. 6. Idealized pressure-displacement curve for plate-loading test. tests. 
208 International Society for Rock Mechanics 
that readings should continue until the rate of displace- 
ment is less than 2~o of the incremental displacement 
per hour may be used. This criterion may be modified 
to suit the purpose of the test. The final increment in 
any one cycle should be held for as long as practical 
if the displacement is still increasing. 
PART 3. SUGGESTED 
METHOD FOR 
MEASURING ROCK MASS 
DEFORMABILITY USING 
A RADIAL JACKING TEST 
SCOPE 
1. (a) This test measures the deformability of a rock 
mass by subjecting a test chamber of circular cross sec- 
tion to uniformly distributed radial loading; the conse- 
quent rock displacements are measured, from which 
Elastic or Deformation modulae may be calculated. 1. 
(b) The test loads a large volume of rock so that 
the results may be taken to closely represent the true 
properties of the rock mass, taking into account the 
influence of joints and fissures. The anisotropic defor- 
mability of the rock can also be measured. 
(c) The results are usually employed in the design 
of dam foundations and for the proportioning of pres- 
sure shaft and tunnel linings. 
APPARATUS 
2. Equipment for excavating and lining the test 
chamber including: 
(a) Drilling and blasting materials or mechanical 
excavation equipment, z 
(b) Concreting materials and equipment for lining the 
tunnel, together with strips of weak jointing material 
for segmenting the lining. 3 
3. A reaction frame usually comprising steel rings of 
sufficient strength and rigidity to resist the force 
applied by flat jacks or pressurising fluid. 4 The frame 
must also act as a waterproof membrane when load 
is applied by water pressure. When load is applied with 
flat jacks the frame must be provided with smooth sur- 
faces; hardwood planks are usually inserted between 
the flat jacks and the steel rings. 
4. Loading equipment to apply a uniformly distributed 
radial pressure to the inner face of the concrete lining, 
including: 
(a) A hydraulic pump capable of applying the 
required pressure and of holding this pressure constant 
* Numbers refer to NOTES at the end of the text. 
to within 5% over a period of at least 24 hr, together 
with all necessary hoses, connectors and fluid. 
(b) Flat jacks, when used for load application 
(Fig. la), should be designed to load the maximum of 
the full circumference of the lining, with sufficient sep- 
aration to allow displacement measurements, and 
should have a bursting pressure and travel consistent 
with the anticipated loads and displacements. 
(c) Water pressure, when used for load application 
(Fig. l b) requires water seals to contain the pressurized 
water between the concrete lining and the reaction 
frame. Special water seals are also required to allow 
the passage of extensometer rods through the lining 
and reaction frame; pressurized water should not be 
allowed to escape into the rock since this will greatly 
affect the test results. 
5. Load measuring equipment comprising one or more 
hydraulic pressure gauges or transducers s, of suitable 
range and capable of measuring the applied pressure 
with an accuracy better than _+2~o. 
6. (a) Displacement measuring equipment to monitor 
rock movements radial to the tunnel with a precision 
better than 0.01 ram. Single or multiple position exten- 
someters conforming with the ISRM "Suggested 
Methods for Monitoring Rock Displacements" should 
be used. Directions of measurement should be chosen 
with regard to the rock fabi'ic and any direction of 
anisotropy. 
(c) Measurements of movement should be related to 
reference anchors rigidly secured in rock, well away 
from the influence of the loaded zone. When using mul- 
tiple position extensometers the deepest anchor may 
be used as a reference provided it is situated at least 
2 test chamber diameters from the chamber lining. 
Alternatively the measurements may be related to a 
rigid referencebeam passing along the axis of the 
chamber and anchored at a distance of not less than 
1 chamber diameter from either end of the chamber 
(Fig. 1). 
PROCEDURE 
7, Preparation 
(a) The test chamber location is selected taking into 
account the rock conditions, particularly the orien- 
tation of the rock fabric elements such as joints, bed- 
ding and foliation in relation to the orientation of the 
proposed tunnel or opening for which results are 
required. 
(b) The test chamber is excavated to the required 
dimensions. 2,6 
(c) The geology of the chamber is recorded and speci- 
mens taken for index testing as required. 
(d) The chamber is lined with concrete) The reaction 
frame and loading equipment are assembled. 
(e) The extensometer holes are accurately marked out 
and drilled, ensuring no interference between loading 
and measuring systems. The extensometers are installed 
and the equipment is checked. 
In Situ Deformability of Rock 209 
A B 
® 0) 
(91 
181 (tO) 
' (161 (21 ", (1) ~ i (151 
J 
i 
~----@ 
Fig. la. Radial jacking test; flat jack loading alternative. 
1. Measuring profile. 2. Distance equal to the length of active loading. 3. Control extensometer. 4. Pressure gauge. 
5. Reference beam. 6. Handpump. 7. Flat jack. 8. Hardwood lagging. 9. Shotcrete. 10. Excavation diameter. 11. Measuring 
diameter. 12. Extensometer drillholes. 13. Dial gauge extensometer. 14. Steel rod. 15. Expansion wedges. 16. Excavation 
radius. 18. Inscribed circle. 19. Rockbolt anchor. 20. Steel ring. 
8. Testing 
(a) The test is carried out in at least three loading 
and unloading cycles, a higher maximum pressure 
being applied at each cycle, v 
(b) For each cycle the pressure is increased at an 
average rate of 0.05 MPa/min to the maximum for the 
cycle, taking not less than 3 intermediate sets of load- 
displacement readings in order to adequately define a 
set of pressure-displacement curves (e.g. Fig. 3). 
(c) On reaching the maximum pressure for the cycle 
the pressure is held constant (___2% of maximum test 
presstlre) recording displacements as a function of time 
until approximately 80% of the estimated long term 
displacement has been recorded (Fig. 4). 8 Each cycle 
is completed by reducing the pressure to near-zero at 
the same average rate, taking a further three sets of 
pressure-displacement readings. 
(d) For the final cycle the maximum pressure is held 
constant until no further displacements are observed. 8 
International Society for Rock Mechanics 
:';. ~i 
Approx 4m 
-:~:..-,,::~ T F,: ~: ..~:,.::r..i!-: "'"a:.' .. . .-... * 
• " ' "" " " "i-'i' ' " • °" " ' "' 
i 
i 
i 
"':.."~ . . . ...r: """ . . ::': : ' ~ : " .~:::..~ ""~ 
LSj:-: ; ' f f ~ . . ~ l%" j "*'q 
II 
, . ' . • , . . , . • . , . . 
[ i ) 
• ~; 5i 
~,o 
" " 7 , 
14 " 
,; j: 
Fig. lb. Radial jacking test equ ipment ; i a l ternat ive loading system using water pressure. 
The cycle is completed by unloading in stages taking 
readings of pressure and corresponding displacements. 
(e) The test equipment is then dismantled, or further 
tests may be required having grouted the rock. 6 
CALCULATIONS 
9. (a) A solution is given only for the case of a single 
measuring circle with extensometer anchors immedi- 
ately behind the lining. This solution, which also 
assumes linear-elastic behaviour for the rock, is usually 
adequate in practice although it is possible to analyse 
more complex and realistic test configurations using 
for example finite element analysis. 
(b) If flat jacks are used, the applied load values are 
first corrected to give an equivalent distributed pressure 
Pl on the test chamber lining: 
~b 
Pl = 2 . rc . r 1 .P,.- 
Pl = distributed pressure on the 
lining at radius rl 
p., = manometric pressure in the 
fiat jacks 
b = fiat jack width 
(see Fig. 5) 
The equivalent pressure P2 at a "measuring radius" i" 2 
just beneath the lining is calculated, this radius being 
In Situ Deformability of Rock 211 
O 
® 
I 
l? L - 
Ill l l l Illlllllll 
A B I q ~ 
L "i I 
[- . . . . . . -l, ~ , F - - - 
--i ® 
///I- 1 
A 
~ i IIIIIIIIIIIIlUlIIIII ] 
\ I Y A " / I / 
A = AAI ÷A&2+~A3=AAI +2ABI 
I_ L! 
I 
i 
i 
I 
Fig. 2. Method of superposition to give displacements for equivalent 
uniformally distributed loading (elimination of end effects). 
(c) Superposition of displacements for two "tic- 
ticious" loaded lengths is used to give the equivalent 
displacements A for an "infinitely long test chamber". 9 
A -- AA1 + AA2 + AA3 = AA1 + 2. An1 
(see Fig. 2 to give symbols) 
(d) The result of the long duration test (Ad) under 
A maximum pressure (max P2) is plotted on the displace- 
ment graph (Fig. 3). Test data for each cycle are pro- 
portionally corrected to give the complete long term 
pressure-displacement curve. The elastic component 
(A,,) and the plastic component (Ap) of the total defor- 
mation (A,) are obtained from the deformation at the 
final unloading: 
A t = A p + A , , (see Fig. 3) 
(e) The elastic modulus E and the deformation 
modulus V are obtained from the pressure-displace- 
ment graph (Fig. 3) using the following formulae based 
on the theory of elasticity" 
E - P 2 " r 2 m + 1 
A Ae m 
v - P 2 " r z m + 1 
At m 
where P2 is the maximum test pressure and m is an 
estimated value for Poissons Ratio. 
(f) Alternatively to (e) above, the moduli of undis- 
turbed rock may be obtained taking into account the 
effect of a fissured and loosened region by using the 
outside the zone of irregular stresses beneath the flat 
jacks and the lining and loose rock. 
rl Eb 
P2 = - - " Pl = - - " Pm" 
r 2 2./t . r 2 
following formulae: 
=p2.rz(m__++ l l n r a~ 
E A e \ m r2 / 
9p 
6,0 
3,0 
L Ad I 
A A ' 2 A B I~ -I 
. ,/ 
-17 q . . . . . I , - A 
50 I00 
m m I00 
Fig. 3. Typical graph of applied pressure versus displacement. 
R.M.M.S. 16/3 D 
212 
O/o A 
International Society for Rock Mechanics 
I00 
80 
P 
Prr~x 
f 
/ 
I/A // 
L btime 
Fig. 4. Typical form of graph for displacement versus time at constant 
applied pressure. 
where i" 3 is the radius to the limit of the assumed fis- 
sured and loosened zone, and In is the Naperian 
(natural) logarithm. 
(g) The dimensions of pressure linings can be deter- 
mined directly by graph. 1 Use the load line of the 
greatest displacement as shown in Figs 3, 6 and 7. 
/ 
Fig. 6. Typical graph showing total and plastic displacements as a 
function of direction perpendicular to the test chamber axis. 
/ \ 
\\ J 
b ~ 
P~ 
\ 
/ 
pro' ~ b = p1.2.~,7r 
Pro" 7-b 
q : 2 . T . ~ 
lq 
r I -; q ~! p~: p,' -¢j- 
Fig. 5. Scheme of loading showing symbols used in the calculations. 
IO 
T 
~6 
o. 
E5 
8 
o. 
~o 
P, 
Pi 
A 
=T- 
5 
~5 
i '° 
Pi = Pr + Ps 
(o = gap between steel 
and concrete 
r 
i0 
1.0 
5O 
I I i 
I00 2O0 500 
o~ t 
Fig. 7. Design chart for direct estimation of pressure tunnel lining 
thicknesses (from Lauffer & Seeber, see NOTE 1). 
In Situ Deformability of Rock 213 
REPORTING OF RESULTS 
10. The report should include the following: 
(a) A diagram giving all dimensions, photographs 
and detailed description of the test equipment, full de- 
scription of the methods used for test chamber prep- 
aration, lining and testing. 
(b) Geological plans and section of the test chamber 
showing the relative orientations of bedding, jointing, 
faulting and any other features that may affect the test 
results, preferably with index test data to give further 
information on the mechanical characteristics of the rock 
tested. 
(c) Tabulated test observations together with graphs 
of displacement versus applied pressure Ps or P2, and 
displacement versus time at constant pressure for each 
of the displacement measuring locations. Tabulated 
"corrected" values together with details of the correc- 
tions applied. See Figs 3, 4 and Table 1 (graphs are 
usually drawn only for the maximum and minimum 
displacements).(d) Transverse section of the test chamber showing 
the total (At) and plastic (Ap) displacements resulting 
from the maximum pressure (e.g. Fig. 6). The orien- 
tations of significant geological fabrics should be shown 
on this figure for comparison with any anisotropy of 
test results. 
(e) The graphs showing displacements as a function 
of applied pressure (e.g. Fig. 3) should be annotated 
to show the corresponding elastic and deformation 
moduli and data from which these were derived. 
NOTES 
1. For the design of pressure tunnel linings, the lining 
thicknesses in the full scale tunnel may be determined 
directly from the results of the test on the "model" 
tunnel. (Lauffer, H. and Seeber, G. "Design and control 
of linings in pressure tunnels and shafts." 7th Int. Conf. 
on Large Dams, Rome 1961, R91, Q25). 
2. The recommended diameter is 2.5 m, with a loaded 
length equal to this diameter. Blasting is only permitted 
if the test results are applied directly as a "model" test 
to the case of a blasted full scale tunnel (see NOTE 
1). Otherwise the chamber should be excavated with 
as little disturbance as possible. 
3. When testing only the rock, the lining should be 
segmented so that it has negligible resistance to radial 
expansion; in this case the composition of the lining 
is relatively unimportant, and it may be of either shot- 
crete or concrete. Alternatively when it is required to 
test the lining together with the rock, the lining should 
not be segmented and its properties should be modelled 
according to those of the prototype. 
TABLE 1. SUGGESTED LAYOUT FOR TEST DATA SHEET 
1 2 3 4 5 4 + 5 6 7 4 + 5 + 7 
Ad 
NR time P2 AA As A A + A a Ad corr. At 
1 
2 
3a 
3b 
3c 
4 
5 
6a 
6b 
6c 
7 
8 
9a 
o0 
8 9 
Ae Ap 
E - P 2 " r 2 m + 1 
A e m 
v - P 2 " r 2 m + 1 
A t fir/ 
214 International Society for Rock Mechanics 
4. Either flat jacks or a pressurizing fluid may be 
used to apply radial pressure to the test chamber; the 
two alternatives are illustrated in Fig. la and b. 
5. Measurements are usually by means of mechanical 
guages. Particular care is required to guarantee the 
reliability of electric transducers and recording equip- 
ment when used. 
6. To assess the effectiveness of grouting, two test 
chambers are usually prepared adjacent to each other. 
Grouting is carried out after completion of testing in 
the ungrouted chamber, and the equipment is then 
transferred to the grouted chamber. 
7. Typically the maximum pressure applied in this 
test is from 5-10 MPa. 
8. In the case of "creeping" rock it may be necessary 
to stop loading even though the displacements con- 
tinue. Not less than 80Y/o of the anticipated long term 
displacement should have been reached. 
9. This superposition is made necessary by the com- 
paratively short length of test chamber in relation to 
its diameter. Superposition is only strictly valid for elas- 
tic deformations but also gives a good approximation 
if the rock is moderately plastic in its behaviour.