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PRESSUREMETER AND DILATOMETER TESTS

INTERPRETATION AND RESULTS

1) PRINCIPLES The pressuremeter and dilatometer tests are in situ loading tests executed by expansion of a cylindrical cavity. The stresses are exerted on the walls of the cylinder drilled in soils or rocks by mean of a pressurized fluid acting on one or several inflatable membranes. The relation between the stresses and the obtained deformations, can be analyzed theoretically at the difference of the other in-situ tests, or empirically according to the hypothesis on the properties of the surrounding materials. Hypothesis • The instrument exerts a radial and uniform field of stresses on a given length of the

probe. This hypothesis is the basis of the conception of the Louis Menard tri-cellular probes.

• The deformations of the soil or rock comprise a pseudo-elastic and a plastic phases. • When the determination of the deformation is done by a volumetric mean, the

medium is considered to be isotropic in the test zone.

Figure # 1-PRESSUREMETER TEST

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Tests in the soils and soft rocks • The instruments are called pressuremeters, although initially the name of

pressuremeter was the brand-name reserved to the Louis Menard apparatus. Tests in the rocks • The instruments are called dilatometers. • Several instruments, which exert stresses on a limited section of the perimeter of the

walls as the Goodman Jack, are very difficult to interpret as the rigid surface in contact with the rock change with the pressure. The instruments, which comprise a flexible membrane, exert a uniform field of stresses as the Probex, or sectorial as the Probe of the Colorado School of Mines are easier to interpret.

2) PRINCIPAL TYPES OF INSTRUMENTS 2.1) PRESSUREMETERS There is two types of instruments which differ by the way of measuring the deformations. In the first type this measure is made by measuring the volume injected to dilate the probe and in the second type is directly made by measuring the variations of diameter of the probe. (Figure # 2)

Figure # 2-PRINCIPLES OF THE DIFFERENTS PRESSUREMETERS

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2.1.1) MENARD PRESSUREMETER( type G,G-Am) ( Figure # 3 ) • Tri-cellular probe giving a uniform radial field of stresses in the central third. • Stress controlled test • Radial deformation deducted from the measurement of the injected volume requiring

the determination of the parasitic dilatation. • Coaxial injection tubing to reduce the parasitic dilatations. • Compressed gas is required to run the test. • Need of training to perform a good test. • Very large number of tests already performed in various materials giving references

of the long-term behaviour of structures and confidence in the use of empirical factors.

Figure # 3-G-Am PRESSUREMETER (Type MENARD)

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2.1.2) TEXAM (Figure # 4) • Mono-cellular probe with measurement of the deformations deducted from the

volume of the injected fluid by mean of a manual actuator. Following studies made by the professor J-L Briaud (Texas A&M),the LCPC ( France ) and ROCTEST, it has been proved than when the ratio between the length and the diameter of the probe is above 10,the results are similar to those of a tri-cellular probe.

• Strain controlled test • No need of compressed gas. • Easy use with few risk of bursting the probe. • Less references than the Menard G-Am pressuremeter.

Figure # 4-TEXAM PRESSUREMETER

2.1.3 ) TRI-MOD (Figure # 5) • Mono-cellular probe pneumatically inflated.

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• Measurement of the deformations according to 3 diameters by mean of arms

instrumented with electrical strain gages. • Allows to measure the anisotropy • Few instruments in use.

Figure # 3-TRI-MOD PRESSUREMETER

2.1.4) PENCEL ( Figure # 6 ) • Mono-cellular probe hydraulically inflated as the Texam • Similar to the Menard Pavement Pressuremeter. Driven in place. • Used for the control of compaction. • A special model with hollow probe can be fitted to a static cone.(Figure # 7 )

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Figure # 6-PENCEL PRESSUREMETER

Figure #7-HOLLOW PENCEL PROBE FITTED TO A STATIC CONE

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2.1.5) BOREMAC ( Figure # 8 ) • Adaptation of an hollow G-Am or TEXAM probe ( diameter N ) to be placed in situ

by self-boring • Less disturbance of soils than the conventional bore-holes. • Delicate use requiring a good training

Figure # 8-SELF-BORING PROBES

2.1.6) OTHER INSTRUMENTS • Self-boring pressuremeter of the French LCPC • Conical Probe of Ladanyi

RETRO-JET

BOREMAC

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2.2 DILATOMETERS Remark: These instruments have many common points with the pressuremeters and are therefore just mentioned in this paper for comparison. Their use and interpretation are also just briefly described. 2.2.1) PROBEX (Figure # 9) • Mono-cellular probe hydraulically inflated by mean of a double ram located just

above the probe to eliminate the parasitic dilatation of the tubing and of the surface ram.

• Measurement of the deformations by monitoring of the displacements of the double

piston with a LVDT. • Does not allow to measure the anisotropy. Involves a large volume of rock. • Requires a careful calibration. Easy to use • Used in standard N size (76 mm or 3 inches) boreholes.

Figure # 9-PROBEX-1 DILATOMETER

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2.2.2) MAZIER DILATOMETER ( DMP-R95 model) (Figure # 10 ) • Mono-cellular probe expanded by mean of a compressed gas • Measurement of the deformations of 3 radius disposed at 120 ° by mean of 3 LVDT • Allows to determine the anisotropy of the rock. • Requires a bore-hole with a diameter of 101 mm ( 4 inches) • Can be used at great depth.

Figure # 10-MAZIER DILATOMETER-DMP model.

2.2.3) SECTORIAL DILATOMETER-COLORADO SCHOOL OF MINES. • Probe comprising 2 pairs of membranes forming 4 areas of loading parallel to the

axis, with 2 different pressures. • Allows to determine the anisotropy and the Poisson ratio in situ. • Experimental prototype. 2.2.4) OTHER INSTRUMENTS • Goodman jack

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3 ) METHODS OF SETTING OF THE PROBE. See the figure # 11 3.1) BORE-HOLE The method to do the borehole must be adapted to the type of rock or soil in a way to reduce the risks of disturbance of the walls. I n the case of the dilatometer tests in rocks, the boreholes are almost always made by drilling with a diamond bit. The other methods with percussion drills do not allow to obtain a good calibration of the hole and furthermore create fractures which modify the properties of rock. The small depth boreholes in cohesive soils can be made by mean of an hand or mechanical auger. For most of the other conditions, the best results are obtained by using tricones or fish-tails with teeth in carbide of tungsten and slurry of bentonite. The importance of the disturbance can be detected by looking at the shape of the pressure versus deformation curve and the ratios between the different parameters as discussed in the following chapter regarding the validation of the results. 3.2) SELF-BORING This method of setting the probe requires a large experience to co-ordinate the speed of rotation, the flow of the fluid used to flush the cuttings and the speed of advancement of the tool. If all these parameters are not adequate there is a risk of disturbance by clogging and pushing of the probe. This method is limited to the fine soils and is only used in particular areas. A probe with inverted cutting edge and retro-jetting has been conjointly developed by Louis Menard and Roctest but although the preliminary results were very satisfying has never been completed for commercial use. 3.3) PUSHING AND DRIVING. These methods which evidently disturb the soils are used in the grounds where the conventional boreholes are difficult to do as the gravel below the water table or the fillings made of ungraded materials. The use of the Pencel has been limited to the control of compaction of granular soils at small depth. The driven slotted casing in which a G-Am type probe in inserted is very frequently used for the control of the dynamic compaction and the evaluation of fills containing blocks. In this special case, slotted casings have already been placed before placing of the fill with insertion of inflatable packers to avoid the crushing of the slotted parts during the compaction.

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Figure # 11-METHODS OF SETTING THE PROBE OF THE PRESSUREMETER 4) RESULTS OF THE PRESSUREMETER TESTS. 4.1) PRESSUREMETER CURVE The figure # 13 represents a typical pressuremeter curve. It shows in the case of an instrument with a volumetric measurement as the G-Am or the TEXAM, the injected volumes in the probe versus the pressures. The Menard test called the normalized test must comprise about 10 steps of pressure of equal increment. This procedure requires a previous estimation of the limit pressure to reach. The readings of the deformations are made at each step of pressure 15 seconds,30 seconds and 1 minute after reaching the pressure level. (Figure #12)

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Figure # 12-TESTING PROCEDURE OF A MENARD Type PMT

The pressures versus volumes curve presents 3 phases. • The recompression phase • The pseudo-elastic phase • The plastic phase and rupture. The creep curve is obtained by drawing the deformations between 30 seconds and 1 minute versus the pressures. It presents also 3 phases. With the TEXAM, the test is run with 20 equal increments of volume The pressures are recorded after 30 seconds.

Figure # 13-NORMAL PRESSUREMETER CURVE-MENARD Type.

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4.2) PARAMETERS OBTAINED FROM A PRESSUREMETER TEST. 4.2.1) LIMIT PRESSURE: Pl. The limit pressure corresponds to the failure of the surrounding soil. It is given by the asymptote of the pressuremeter curve. As this asymptote is not always easy to define, an other definition as been given to the limit pressure which corresponds to the pressure for which the volume of the initial cylindrical cavity has doubled. This value takes into account the pressure of inertia of the probe Pi which is generally very small (Pi< 50 kPa) and is often neglected excepted in the soft clays.(Figure # 14 ) For the normal tests with the standard probes for which the “at rest” volume Vc is 535 cc. , and the injected volume Vo at the contact with the walls is about 100 cc. ,the limit pressure corresponds to an injected volume of about 700 cc.( Vc +2 Vo) To complement the previous method called manual to estimate the abscise of the asymptote of the normal curve, 3 other methods of extrapolation have been developed and are used when the test has reached the plastic phase but not the limit pressure. It must be noted that in fact the test is always interrupted before reaching this pressure to avoid the bursting of the probe. If Vc is the “at rest”volume of the probe and Vo the injected volume necessary to obtain the contact with the walls of the borehole, Vi the initial volume of the cavity is given by Vi = Vc +Vo. If we call V the total injected volume, the 3 methods are defined as follows: (Figure # 15) • The log- log method for which the curve of pressures is drawn in logarithmic

coordonnates in function of V-Vo/Vc+Vo. This curve presents a straight segment in the plastic phase and the limit pressure is reached when the previous relation is equal to 1.

• The relative volumes method for which the curve of the pressures is drawn in function of V-Vo/Vc+V. This curve also presents a straight segment in the plastic phase and the limit pressure is reached when the previous relation is equal to 1/2.

• The method of the inverted volumes for which the curve of the pressures is drawn in function of 1/V.As for the previous methods this curve is a straight line in the plastic phase, and the limit pressure corresponds to V=700 cc for the standard probes. This last method is described in the D 60 general brochure. The figures #16 and 17 show an example of use of this method.

At the obtained value must be subtracted the value of the pressure of inertia Pi,and added the hydrostatic pressure due to the column of fluid filling the tubing between the probe and the measuring instrument located at ground level.

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Figure #14-PRINCIPLE OF DETERMINATION OF THE LIMIT PRESSURE Pl.

Figure # 15-DETERMINATION OF Pl WITH THE LOG-LOG METHOD AND THE RELATIVE VOLUMES METHOD.

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VVcVV

vol.Total cavity V

or 1VVcVV

vol.Initial cavity V 0

0

0 =+

−=

∆=

+−

=∆

0

0

VVcVV

+−

VVcVV 0

+−

15

Figure # 16-DETERMINATION OF Pl.WITH THE INVERTED VOLUMES METHOD (Data )

Figure # 17-DETERMINATION OF Pl.- THE INVERTED VOLUMES

METHOD (data taken from figure # 16)

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4.2.2) PRESSUREMETER MODULUS The pressuremeter modulus E is based on the Lame equation giving the radial increment of a radial cavity in function of the pressure in an elastic medium. The formula which gives the Shear modulus G is: G= Vx ?P/?V where V is the volume of the cavity and P the pressure in this cavity. ?P/?V is the slope of the pressuremeter curve in its linear pseudo-elastic part, taken for the volume Vm, located in the middle of the segment Vo-Vf. Vo is the volume corresponding to the pressure of recompression of the walls of the borehole, which is more or less the “at rest” pressure of the soil. Vf corresponds to the creep pressure. In an elastic medium the relation between the shear modulus G and the Young modulus E is: G = E/2( 1+? ) where ? is the Poisson ratio. In the case of the pressuremeter modulus Em, the Poisson ratio is equal to 0,33. If Vc is the “at rest”volume of the probe, we obtain:

Em =2,66 (Vc +Vm )x ?P/?V ( Figure # 18 )

In the following paragraphs we will write E instead of Em as being the pressuremeter modulus. This is a distortion modulus measured in a deviatoric field of stresses which is different from the oedometric modulus. The figure # 19 shows a calculus of the modulus E.

Figure # 18-PRINCIPLE OF DETERMINATION OF THE PRESSUREMETER

MODULUS E.

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Figure # 19-EXAMPLE OF CALCULUS OF THE MODULUS E

In the example of the previous figure, we have: Po =150 kPa Pf =800 kPa vo= 150 cc. vf= 250 cc. Vc= “at rest “volume of the probe = 535 cc. ?pi (between vo and vf ) =25 kPa vm= 200cc.

E=2,66 Vm x ? P/? V

Vm =vm+Vc = 735 cc. ? P =? p-? pi = 650-25 =625 kPa. ?V =?v =100 cc.

E = 2,66x735x(625/100) = 12200 kPa.

4.2.3) CREEP PRESSURE Pf This pressure corresponds to the end of the pseudo-elastic phase. Although this value is not used as a parameter to calculate the foundations, it is important to determine it to validate the results.

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4.3) VALIDATION OF THE RESULTS OF A PRESSUREMETER TEST. 4.3.1) SHAPE OF THE PRESSUREMETER AND CREEP CURVES Normal pressuremeter and creep curves comprise 3 well defined parts when the test is run in a bore-hole.(Figure # 13 ) • The phase of recompression of the ground which presents a concavity toward the axis

of pressures for the curve pressure versus volume, and a segment of straight line with a negative slope for the creep curve.

• The pseudo-elastic phase where the pressuremeter curve is a straight line with a

positive slope and a segment of straight line with a small positive slope fo r the creep curve.

• The plastic phase and failure with a concavity toward the axis of volumes and a

vertical asymptote for the pressuremeter curve and a segment of straight line with a large positive slope for the creep curve.

When the test is perfectly realized, the creep curve shows a very well defined point between the 2 last phases which is a confirmation of the validity of the test. 4.3.2) RATIOS BETWEEN THE DIFFERENT PARAMETERS. Statistical data allow to confirm the validity of the results. • The ratio between the creep pressure and the limit pressure must be between 1/2 and

2/3 1/2 < Pf/Pl < 2/3.

• The ratio between the modulus and the limit pressure must correspond to the type of

ground. In over-consolidated soils, this ratio must be between 12 and 30

12 < E/Pl < 30 In the alluvial soils (sand, gravel, silty sand below water) this same ratio is comprised between 5 and 8

5 < E/Pl < 8 4.3.3) CORRELATIONS WITH THE OTHER TYPE OF IN-SITU TESTS. When, other in-situ test have been made in the same ground, as the Standard Penetration Test (SPT) giving the index N, the Dynamic Cone Test giving the index D, or the Static Penetration Test which gives the point resistance Rp, it is possible to compare the obtained results by using the following mean correlations.

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• In clays Rp=3 Pl

• In the fills made of clayey silt.. N=200 to 250 Pl

• In silty sand D=250 Pl Rp=6 Pl

• In the fills made of sand and gravel. N=350 to 400 Pl Rp=9 Pl

• In all types of soils. CBR index=1,7 Pl. In the previous relations, Pl, Rp, are expressed in kPa, and N and D in number of blows.

4.3.4) INFLUENCE OF THE METHOD OF SETTING THE PROBE. Several comparisons have been made between the tests made with a rammed slotted casing and the conventional boring methods with a tri cone or fishtail and a slurry of bentonite. The following observations have been noted. • The modulus and the limit pressure are increased in the compact granular soils above

the water table. • The limit pressure and above all the modulus are reduced for the tests run at shallow

depth and below the water table. An example is given in the table # 1.

SLOTTED CASING METHOD

PARAMETERS FISHTAIL WITH BENTONITE SLURRY

410 kPa Pl 440 kPa 2880 kPa E 3570 kPa

7,0 E/Pl 8,1

Table # 1-INFLUENCE OF THE SETTING METHOD.

The previous tests have been run in a fine silty sand at a depth varying between 1 and 4 meters, below the water table.

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5) UTILIZATION OF THE PRESSUREMETER RESULTS. 5.1) BEARING CAPACITY. A pressuremeter is essentially an in situ loading test run up to failure. The theories and numerous experiments have shown that the bearing capacity at failure is proportional to the limit pressure Pl of the ground. The factor of proportionality is function to the relative depth and shape of the foundation and also of the type of ground. If we call Ql the bearing capacity at failure Qo the natural vertical pressure of the ground at the foundation level after construction. Pl the limit pressure Po the “at rest”horizontal pressure of the ground at the test level. K the bearing factor. We have the relation:

Ql-Qo = K (Pl-Po) Rule Ro

To define the factor K, the Techniques Louis Menard have classified the materials in 4 categories (Table #2 )and run a large number of tests on various types of foundations.

RANGE OF Pl in kPa TYPE OF SOIL CATEGORY 0-1200 0-700

CLAY SILT

I

1800-4000 1200-3000 400-800

1000-3000

COMPACT CLAY COMPACT SILT

COMPRESSIBLE SAND SOFT ROCK

II

1000-2000 4000-10000

SAND AND GRAVEL ROCK

III

3000-6000 VERY COMPACT SAND AND GRAVEL

IIIA

Table # 2-CATEGORIES OF GROUND.

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The values of the bearing factor K are given in the D60 manual and shown in the figure #20. The minimum value of K is 0,8 and corresponds to a foundation built on the surface of the ground. We remark that below a given relative depth h/R , where R is the half width of the foundation and h its depth, the K factor becomes constant. This depth is called the critical depth and varies from 4 for the circular or square footings in clays, to 22 for the strip footings in the very dense sands and gravel.

Figure #20-BEARING FACTOR K IN FUNCTION OF THE EMBEDMENT

• HETEROGENEOUS GROUNDS. When the properties of the ground in which the foundation is built vary with the depth,it is necessary to use an equivalent limit pressure Ple. The ground is divided in layers with a thickness equal to half the width of the foundation. If we call Pl’1 the geometrical mean value of the limit pressures of the layers which are between 3R and +3R above the foundation, Pl’2 the geometrical mean value for the layers located between +R and –R (just above and below the foundation level ) and Pl’3 the geometrical mean value for the layers located between –R and – 3R.below the foundation, we obtain: Ple = 3 Pl'3Pl'2Pl'1 ×× For the shallow foundation, Pl’1 is not taken into account and Ple is equal to the square root of the product of the 2 other values.(Figure # 21 )

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3 3'2'1' xPlxPlPlPle =

Figure # 21-DETERMINATION OF THE EQUIVALENT LIMIT PRESSURE

An example of the calculation of the bearing capacity of a footing is given in annex. • BEARING CAPACITY OF DEEP FOUNDATION. ( Figure # 22 ) The bearing capacity of deep foundation comprises 2 elements: -the point resistance which is calculated as previously with the bearing factor K -the lateral friction which comprises 2 values: S1 applied on an height equal to 3 diameters above the basis of the pile S2 applied to the remaining length.

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Figure # 22-BEARING CAPACITY OF A PILE.

Q = Qp + Qf (S1, S2)

In the very compressive soils which still settle under their own weight (see thereafter level of auto-bearing.) the lateral friction becomes negative. It is called S3 and for E <1500 kPa S3 is taken equal to 10 kPa. When extra fill or load are added, the value of S3 is increased in function of Pl.(Figure # 23 )

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Figure # 23-NEGATIVE LATERAL FRICTION.

• LEVEL OF AUTO-BEARING The level of auto-bearing is the value of the characteristics that the soil must reach to avoid settlement under its own weight. This notion is particularly important fo r the recent fills. This level can be defined by its limit pressure and varies with the type of soils. For a layer of 0 to 10 meters the following values have been given for different types of soils:

- clays : Pl = 250 to 300 kPa - silts : Pl = 400 kPa - sands : Pl = 600 kPa - sands with gravel and stones : Pl =800 kPa

5.2) SETTLEMENT. According to the Menard theory, the settlement W of a foundation comprises 2 elements. (Figure # 24) The first called W1 corresponds to a volumetric compression under the influence of the spherical component of the stress field. The second called W2 is due to shear deformation caused by the deviatoric component of the stress field. The equation giving the total settlement of a foundation W = W1 + W2 is called the rule To.

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Figure # 24-PRINCIPLE OF THE SETTLEMENT CALCULATION.

RpERo

RpRo

EW 32 5.43

33.1λ

αλ

α

+

=

E is the pressuremeter modulus. Ro is a reference length equal to 30 cm. p is the pressure contact added to the soil in kg/cm2 ( 0,01 kPa.) ?2 and ?3 are the coefficients of shape, function of L/2R R the radius of the foundation a a coefficient of structure The values of a vary between 1 for the over-consolidated clays to 0,25 for the disturbed sands and gravel. (Table # 3 ) The values of ?2 vary between 1 for the square or circular foundations and 2,65 ratio L/2R is equal to 20.( Table # 4 ) The values of ?3 vary between 1 and 1,5 for the previous conditions. All these values are given in the D60 manual.

CLAY SAND SAND-GRAVEL TYPE OF SOIL E/Pl a E/Pl a E/Pl a Over-

consolidated >16 1 >12 1/2 >10 1/3

Normally consolidated

9-16 2/3 7-12 1/2 6-10 1/4

Disturbed or weathered

7-9 1/2 1/2 1/4

Table # 3-STRUCTURE COEFFICIENTS.

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L/2R 1-Circle 1-Square 2 3 5 20 ?2 1 1,12 1,53 1,78 2,14 2,65 ?3 1 1,1 1,2 1,3 1,4 1,5

Table # 4-SHAPE COEFFICIENTS.

The very large number of foundations for which the settlements have been calculated with the previous empirical formula has shown that the results were closed to those observed after construction, exception made of the large rafts on very compressive clays. This observation can be explained by the fact that the expression W2 corresponding to spherical component of the tensor then becomes important and is better evaluated by the oedometric tests. CASE OF THE HETEROGENEOUS GROUND. Generally the pressuremeter modules vary with the depth. To take this variation into account, two equivalent moduli Ea and Eb corresponding respectively to the spherical and deviatoric field of stresses are used to calculate the total settlement W. To calculate Ea and Eb the ground is divided in horizontal layers having a thickness of of R equal to the half width of the foundation, to a total depth of 16 R. If 1 corresponds to the first layer, located in contact with the basis of the foundation, and 16 the deepest layer, we obtain:

À1698,7,65,4,321 5,21

5,211

85,011

4

EEEEE

EB++++

=

The moduli which represent several layers are the harmonical means of the corresponding layers.(See the D60 manual for more details.) • Case of the shallow pressuremeter profiles. When the tests have not been run up to a depth equivalent to 16R, the previous formula giving Eb is simplified as follows: -for the tests run to a depth of 8R

8,7,65,4,321 5,211

85,011

6,3

EEEE

EB+++

=

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-for the tests run to a depth of 5R

5,4,321

185,011

2,3

EEE

Eb++

=

• Case of the two-layers. This is the frequent condition of a raft founded on a soft layer, with a thickness inferior to half the width of the foundation and overlying a substratum regarded as uncompressible as the bedrock. The used formula is named the rule T5 in the manual D60. The formula takes into account the repartition in elasticity of the stresses below the foundation and the moduli corresponding to the same depths, and the coefficients of structure a already defined in addition to a coefficient ß function of the adopted value of the safety factor. This factor is the conventional ratio between the bearing capacity at failure and the effective chosen level of stress, in function of the depth. • Case of the closed or grouped foundations. This problem is complex due to the superposition of the field of stresses of each individual foundation. By example in the case of 3 parallel strip footings, we have to consider 4 elementary fields and the total settlement is the sum of 4 terms corresponding to these 4 fields. This corresponds to add to the settlements of each individual foundation, the settlement of a fictitious foundation with a width equal to the total area covered by the footings and a pressure equal to the mean pressure Pm that the building will impose on a general raft. • Case of the foundation built on the bottom of an excavation. The excavation of ground creates a reduction of stresses in the different underlying layers and a heaving of the bottom of the excavation. The calculus of the settlement comprises 2 phases. -a first phase corresponding to the load exerted by the structure in addition of the pre-existing stress. -a second phase corresponding to the re-establishment of the previous level of stresses existing before excavation and for which is used the alternate modulus Ea. In the case of Ea has not been measured during the pressuremeter tests, the following approximate values are used depending of the type of soil.

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Type of soil Ea/E Clay 2 Silt 3

Sand and gravel 4

5.3) RESISTANCE TO A LATERAL LOAD. Several methods of calculation of the structures submitted to lateral forces require the determination of a modulus of reaction called generally k. This modulus is based on the hypothesis that the deformations d are proportional to the stresses p.

P= kxd This modulus does not take the dimension of the structure into account. The modulus k can be deducted from the pressuremeter tests by dividing the 2 terms giving the total settlement by the pressure p. (Rule To)

1/k=(W2+W3)/p An approximation of the modulus of reaction can also be obtained for the rigid or flexible foundations with the following formula:

k=axE/2R The parameter a varies with the coefficient of structure a of the soil from 1,33 for the soft clays to 2,8 for the sands and gravel. The figure #25 shows the basis of calculation of the rigid foundations submitted to a lateral load.

Figure #25-RIGID FOUNDATION SUBMITTED TO A LATERAL LOAD.

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Kz =Kd (z/D)xb. Where Kz is equal to the modulus of reaction at the depth D. b=0 for an ideal cohesive soil. b=1 for an ideal frictional soil.

5.4) SPECIFIC PARAMETERS. Several studies have been made to deduct the specific parameters as the angle of friction and the cohesion of soils from the pressuremeter tests. Papers with abacus giving these parameters in function of Pl are available but the results are not sufficiently confirmed to use them with confidence in the calculations as the slope stability analysis. However these results can be used with precaution in the case of undrained tests to approximate the total cohesion or in the case of well drained tests to obtain the intrinsic angle of friction of very pervious sand or gravel. 5.5) COMPACTION CONTROL. Excepted for the dynamic compaction and the vibroflotation, the pressuremeter tests have been rarely used for the control of compaction. They, however, present numerous advantages in this field by comparison with the traditional methods of control. -testing in depth -immediate results. -direct measure of Pl and E instead of the density. -very sensitive method.As an example,when the dry density increases only by 4% in the silty sand with gravel,the limit pressure doubles. 6) LIMITATIONS IN THE USE OF THE PRESSUREMETER RESULTS. The pressuremeter tests being in situ loading tests run up to failure, it is recommended to use them in similar applications such as the determination of the bearing capacity of foundations. Furthermore, as a large number of tests on real foundations as footings of limited dimensions and strip footings have been run to measure their bearing capacity and settlement, the use of the pressuremeter is reliable to calculate the settlements. On the other hand, the settlement of large rafts on soft clays must be complemented by laboratory tests. In fact, the French LCPC recommend to do a complementary study with oedometer tests in the case of wide foundations ( rafts or fills ) for all soft soils, peat, and saturated sands and silts when their modulus E is below 5000 kPa, or when the values obtained for the settlement is above 20 cm in the soils of greater modulus. The studies requiring the knowledge of the specific values as the angle of friction or the cohesion must be examined with great care.

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In every case, the pressuremeter profiles must be complemented by detailed geotechnical profiles as the presence of heterogeneity such as a layer of low resistance in a more resistant material modifies completely the field of stresses and invalidate the results obtained with the standard methods. The distance between two tests in a profile must be reduced and in the order of 1 meter, and it is recommended to have a continuous sampling. 7)RESULTS AND USE OF DILATOMETER TESTS. 7.1) PERFORMANCE OF A DILATOMETER TEST. There is no standardized dilatometer test as for the Menard pressuremeter test. The increments of pressure are generally defined in function of the maximum capacity of the instrument, as it is unusual to reach the failure of the rock unless it is a very soft rock. This maximum capacity is given by the manufacturer and is a function of the diameter reached during the test. At each level of pressure, the deformations are registered every minute, or in continue if an automatic data acquisition system is available, and the pressure is kept constant until stabilization of the deformations. In fact as the time required to reach the stabilization can be very long, some users have fixed their own rule to define the procedure. By example, a new increment of pressure can be made when the difference of deformations in the last 2 minutes is less than 5% of the same difference obtained in the first 5 minutes. When the maximum pressure is reached, the unloading cycle is made. The pressure is reduced to the value corresponding to the pressure of contact, by steps as for the loading cycle, until the stabilization is reached. For all types of dilatometers, the calibration tests giving the parasitic dilatation ?v/?p of the instrument (probe, tubing and readout) are very important. This value limits the use of the high-pressure pressuremeter to the soft rocks when the Mazier dilatometer can be used in rocks having moduli of 5000 to 50000 Mpa. 7.2) PARAMETERS OBTAINED WITH A DILTOMETER TEST. The results are presented as a graphic showing a series of loops of hysteresis from which several moduli can be calculated depending of the problem to solve. (Figure # 26 ) • Modulus of initial loading E.

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• Modulus of unloading Er. The ratio between the first loading modulus and the unloading modulus E/Er varies generally between 1 and 3 and can even reach 5 in heavily fractured rocks.

• Hysteresis.

Figure # 26-DILATOMETER TEST.

7.3)UTILIZATION OF THE RESULTS. The dilatometer tests are used to evaluate the deformations of rocks according to their different variations of the field of stresses. The moduli calculated from the test results are generally used in elasticity analysis or with the finite elements analysis in the following applications: • Deformations of the foundations of a concrete dam. • Deformations of the walls and roof of underground excavations such as underground

power-plant and tunnels.

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• Design of pressurized penstocks in rock. • Deformations of the supports of bridges or other large structures as the arches of the

biodome in Montreal. REMARKS. In the soft rocks the high-pressure pressuremeter tests allow to obtain a good approximation of the loading and cyclic moduli. The pressuremeter tests run in rocks require the use of high-pressure equipment and in particular of tubing in Tecalan instead of Rilsan as for the standard apparatus. Special calibration tests are run to determine the parasitic dilatation. They are made by placing the probe in a thick wall steel tube. The parasitic deformation is then calculated: a=?v/?p. The formula giving the pressuremeter modulus becomes:

E= 2(1+?)/(?V/?P-a)

We can see that to obtain a significant test in rock the value of “a” must be small and repetitive. When the saturation of the pressuremeter (apparatus, tubing and probe)is perfectly done the maximum significant modulus is in the order of 2,5 millions of kPa.. Additional information regarding the use and the interpretation of the pressuremeter in rocks can be found in the manuals D3, D21, and D35 of the Techniques Louis Menard. The tables #5 and 6 give a comparison of the moduli obtained with a pressuremeter and those obtained with a Goodman Jack (Peace River-Site C ) and Plate Loading Tests ( dam of Chulac-Guatemala)

MODULUS OF DEFORMATION in MPa GOODMAN JACK

BOREHOLE

?=45°(Hustrulid) ?=30°(Salem) PRESSUREMETER

1 1430 900 1120 2 1720 1100 1030 3 2270 1440 1030 4 1080 690 450 5 2720 1730 1560

Table # 5-COMPARISON BETWEEN THE MODULI OBTAINED WITH THE

PRESSUREMETER AND THE GOODMAN JACK.

Project: Peace River-Site C-Canada Type of rock: weathered shale.

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MODULUS IN MPa TYPE

OF TEST Maximum Minimum Mean PRESSUREMETER 4500 900 2300 PLATE LOADING 3600 400 2000

Table #6-COMPARISON BETWEEN THE MODULI OBTAINED WITH THE

PRESSUREMETER AND PLATE LOADING TESTS

ANNEXES

ANNEXE-1 Example of calculation of the bearing capacity of a foundation with the pressuremeter tests. Square footing with a length of 2 meters. Depth of foundation: 3,5 meters. Type of soil: sand and gravel with the properties as shown on the figure # 27, where Pl and E are given in kPa.

Figure #27-EXAMPLE OF CALCULATION OF A BEARING CAPACITY

490600x400Pl1 ==

10901000x1200Pl2 ==

1340150012003 == xPl

890134010904903 == xxPle

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Ql=K (Ple-Po)+Qo Ple=890 kPa Qo=?h=2,0x350=700 kPa Po=KoxQo=0,5 x700=350 kPa h/R=3,5 Soil category: III K=3

Ql=3(890-350)+700=2635 kPa

ANNEXE-2 Example of calculation of the settlement of a foundation with the pressuremeter tests. Conditions as described in the previous annexe 1 (Figure #26) p=1/3 Ql=850 kPa square footing -R=100 cm -Ro=30 cm ?2=1,12 ?3=1,1

RpEARo

REB

w 32 5.4xpRo

333.1

λα

λα

×+

•=

a=1/3 (sand and gravel with E/Pl>10)

EB= kPa116001

85,011

2,3

5,4,321

=++

EEE

EA=E1=950 kPa

W=1,51+0,73=2,24 cm