Módulo 2 y 3 Práctica –ensayos in situ...2006/12/01 · Práctica –ensayos in situ (84.07)...

Módulo 2 y 3Práctica – ensayos in situ

(84.07) Mecánica de Suelos y Geología

M. Codevilla: [email protected]

mailto:[email protected]

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A.O.Sfriso Modulo 2 - 2c 2020.docx 20-nov.-20

6.7 ¿Puedo determinar en forma directa LL, LP, #200 en un ensayo PMT?

6.8 A continuación se presentan los resultados de un ensayo S-CPTu efectuados en la localidad de Amherst, Massachusetts. Se pide determinar a los 3m, 6m y 12m de profundidad:

• El tipo de suelo detectado (considerar 9:ba~160=/?@, NF=NTN) en función de la clasificación de suelos propuesta por Robertson (SBT - original).

• La resistencia al corte no drenada _å y la sensitividad † (considerar =úa = 12). • El coeficiente de consolidación Å• obtenido en los ensayos de disipación de presión de poros. • El módulo de corte a baja deformación ]8.

(nota: el piezcono eléctrico tiene un área de 10cm2, relación de área ( = 0.8 y la presión de poros Ç¶ = ÇV)

Figura. Ensayo S-CPTu.

6.9 En base a los datos del ejercicio anterior, ¿a qué profundidad recomendaría fundar una base

aislada de una estructura liviana?

6.10 En base al manual EPRI en lo referente al ensayo PMT (ensayo presiométrico, apéndice C) ¿Qué representan los valores 2ß y 28? ¿Cuál es más grande que el otro? ¿Siempre obtengo los dos resultados en una prueba?

6.11 En base al manual EPRI en lo referente al ensayo VST (ensayo presiométrico, apéndice E), enumere 3 posibles fuentes de error en dicho ensayo y como incide en la medición.

6.12 Un ensayo VST (® = 65?? , ℎ = 130?? , 6 = 2??) efectuado en una perforación a 7m profundidad permitió determinar que el valor de la resistencia al corte no drenada es de 12kPa. Determine el valor del torque máximo aplicado en el ensayo y determine el valor de sensitividad sabiendo que el valor del torque residual fue la 1/5 del valor del torque máximo.

6.13 En un ensayo DMT efectuado a 3m de profundidad en un suelo saturado con 9 = 17.20=/?@ se midieron los siguientes valores: 28 = 940'( , 2p = 2350'(. Se pide determinar los valores ©™, ™́, !™. ¿Se puede estimar si el suelo está normalmente consolidado o preconsolidado en base a los resultados obtenidos?

6.14 En un ensayo PMT efectuado a 8m de profundidad en un suelo con 9 = 190=/?@, sin presencia de nivel freático, se midieron las siguientes presiones durante el ensayo: 28 = 900=/?V, 2I =1900=/?V y 2ü = 2600=/?V. Se pide determinar la presión horizontal in situ del terreno en estudio y su coeficiente de empuje en reposo 8́.

Overview Paper on In-Situ Testing - Singapore Workshop, Nov. 29- Dec. 01,2006 - P.W. Mayne - 9

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Tip Stress, qt (MPa)

Dep

th (m)

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Sleeve fs (kPa)

-0.2 0.0 0.2 0.4 0.6

Porewater ub (MPa)0 100 200 300 400

Shear Wave,VS (m/s)

10 100 1000 10000

Time Rate, t50 (s)

been developed for PMT (Fahey & Goh 1995; Clarke & Gambin 1998) and DMT (Robertson et al. 1998; Marchetti et al. 2001). The most popular CPTù method at present is the strain path method (SPM) solution of Houlsby & Teh (1988), although other available procedures are dis-cussed by Jamiolkowski et al. (1985), Senneset et al. (1988, 1989), Danzinger et al. (1997), Burns & Mayne (1998, 2002), and others. In terms of calibrating an approach, a fairly comprehensive study between lab cv values and piezocone ch values in clays and silts was reported by Robertson, et al. (1992). Assumptions were made between the ratio of horizontal to vertical permeability to address possible issues of anisotropy during interpretation. The study compared laboratory-determined results with the SPM solution (Teh & Houlsby 1991) using data from type 1 piezocones (22 sites) and type 2 piezocones (23 sites), as well as 8 sites where backcalculated field values of cvh were obtained from full-scale loadings. With the SPM approach in practice, it is common to use only the measured time to reach 50% consolidation, designated t50. As such, if dissipation tests are carried out at select depth intervals during field testing, a fairly optimized data collection is achieved by the SCPTù since five meas-urements of soil behavior are captured in that single sounding: qt, fs, ub, t50, and Vs. The results of a (composite) SCPTù in the soft varved clays at the NGES in Amherst, Massachusetts are de-picted in Figure 29. Here the results of a GT sounding are augmented with data from a separate series of dissipations conducted by DeGroot & Lutenegger (1994).

Figure 29. Seismic piezocone test with dissipations (SCPTù) at the Amherst soft clay test site. In lieu of the focus on a single point corresponding to 50% degree of consolidation (U50), other degrees of dissipation can be considered, or even better, an entire range of consolidation data points starting from penetration through the entire testing time. As such, Houlsby & Teh (1988) provided time factors for a range of porewater pressure dissipations. The degree of excess pore-water pressure dissipation can be defined by: U* = ∆u/∆ui, where ∆ui = initial value during penetration. The modified time factor T* is defined by:

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where t = corresponding measured time during dissipation and a = probe radius. The SPM solu-tions between U* and T* for midface u1 and shoulder u2 piezo-elements are shown in Figures 30 and 31, respectively. These can be conveniently represented using approximate algorithms as shown, thus offering a means to implement matching data on a spreadsheet.

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Overview Paper on In-Situ Testing - Singapore Workshop, Nov. 29- Dec. 01,2006 - P.W. Mayne - Page 29

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Shear Wave,VS (m/s)

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Ejercicio 1: repaso ensayo CPTuM

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Ejercicio 1: repaso ensayo CPTuM

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Ejercicio 1: resolución

• Clasificar al suelo según SBT

• Calcular los adimensionales !" # $%

¿ Qué datos utilizamos de la información recibida para calcular cada uno de los parámetros?

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• Clasificación SBT

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datos:

prof. qt fs ub=u2 t50 Vs

(m) (MPa) (kPa) (MPa) (seg) (m/seg)

3 2,6 30 0,025 150 200

6 0,4 5 0,35 600 150

12 0,8 10 0,45 600 140

resolución:

prof. sv s´v qn=qt-sv Qt=qn/s´v Fr=fs/qn Bq=(u2-u0)/qn

(m) (kPa) (kPa) (MPa) (-) (-) (-)

3 48 18 2,55 0,142 1,18% -0,002

6 96 36 0,30 0,008 1,64% 0,954

12 192 72 0,61 0,008 1,64% 0,543

Clasificación Robertson

prof.

(m)

3 1 suelo fino sensitivo

6 1 - 2 suelo fino sensitivo - orgánico

12 1 - 2 suelo fino sensitivo - orgánico

SBT

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• Resistencia al corte no drenada y sensitividad &' − ) ?

• Coeficiente de consolidación *+ ?

• Módulo transversal ,- ?

¿ Qué datos utilizamos de la información recibida para calcular cada uno de los parámetros?

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Ejercicio 1: resoluciónM

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Resistencia al corte no drenada y sensitividadprof. su=(qt-sv)/Nkt su,r=fs(m) (kPa) (kPa)3 213 30 76 25 5 5

12 51 10 5

Coeficiente de consolidación chprof. t50 Qt=qn/s´v ch(m) (min) (-) (m^2/seg)3 2,5 0,142 6,7E-066 10 0,008 1,7E-06

12 10 0,008 1,7E-06

Módulo de corte a baja deformaciónprof. g r Vs G0(m) (kN/m3) (kN.seg2/m4) (m/seg) (MPa)3 16,0 1,631 200 656 16,0 1,631 150 37

12 16,0 1,631 140 32

S

&' =/" − 0123"

) =&'&',%

,- = 5 6 789

*+ = 1.67 10?@ 6 10A?BCD("FG

A HIJ)

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Ejercicio 2: repaso ensayo DMTM

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Ejercicio 2: repaso ensayo DMTM

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Table 1. Basic DMT reduction formulae

SYMBOL DESCRIPTION BASIC DMT REDUCTION FORMULAE p0 Corrected First Reading p0 = 1.05 (A - ZM + ∆A) - 0.05 (B - ZM - ∆B) p1 Corrected Second Reading p1 = B - ZM - ∆B

ZM = Gage reading when vented to atm. If ∆A & ∆B are measured with the same gage used for current readings A & B, set ZM = 0 (ZM is compensated)

ID Material Index ID = (p1 - p0) / (p0 - u0) u0 = pre-insertion pore pressure KD Horizontal Stress Index KD = (p0 - u0) / σ'v0 σ'V0 = pre-insertion overburden stress ED Dilatometer Modulus ED = 34.7 (p1 - p0) ED is NOT a Young's modulus E. ED

should be used only AFTER combining it with KD (Stress History). First obtain MDMT = RM ED, then e.g. E ≈ 0.8 MDMT

K0 Coefficient Earth Pressure in Situ K0,DMT = (KD / 1.5)0.47 - 0.6 for ID < 1.2 OCR Overconsolidation Ratio OCRDMT = (0.5 KD)1.56 for ID < 1.2

cu Undrained Shear Strength cu,DMT = 0.22 σ'V0 (0.5 KD)1.25 for ID < 1.2

ϕϕ Friction Angle ϕsafe,DMT = 28° + 14.6 log KD - 2.1 log2 KD for ID > 1.8 ch Coefficient of Consolidation ch,DMTA ≈ 7 cm2 / Tflex Tflex from A-log t DMTA-decay curve kh Coefficient of Permeability kh = ch γw / Mh (Mh ≈ K0 MDMT ) γγ Unit Weight and Description (see Marchetti 1999a)

MDMT = RM ED if ID ≤ 0.6 RM = 0.14 + 2.36 log KD if ID ≥ 3 RM = 0.5 + 2 log KD if 0.6 < ID < 3 RM = RM,0 + (2.5 - RM,0) log KD

with RM,0 = 0.14 + 0.15 (I D - 0.6) if KD > 10 RM = 0.32 + 2.18 log KD

M Vertical Drained Constrained Modulus

if RM < 0.85 set RM = 0.85

u0 Equilibrium Pore Pressure u0 ≈ p2 ≈ C - ZM + ∆A In freely-draining soils An example of DMT results is shown in Figure 2. The results are used as follows: − ID (Material Index) gives information on soil type

(sand, silt, clay). − M (vertical drained constrained modulus) and cu

(undrained shear strength) in the usual ways. − The profile of KD (Horizontal Stress Index) is

similar in shape to the profile of the overconsolidation ratio OCR. KD ≈ 2 indicates in clays OCR = 1, KD > 2 indicates over-consolidation. A first glance at the KD profile is helpful to "understand" the deposit.

3 DMT vs OTHER PENETRATION TESTS

(a) Comparative studies have indicated that the DMT results (in particular KD) are noticeably reactive to factors that are scarcely felt (especially in sands) by other tests, such as stress state/history, aging, cementation, structure. Such factors are scarcely reflected e.g. by qc (cone penetration resistance from CPT) and by NSPT, and in general, also due to the arching phenomenon, by cylindrical-conical probes (Marchetti 1999a). Yet such factors are of primary importance in determining some basic soil properties, e.g. deformability and (in sands) resistance to liquefaction. (b) The DMT provides two independent parameters, while most of the penetration tests just provide one "primary" parameter (the penetration resistance) for the interpretation. It is known that in situ tests represent an "inverse boundary conditions problem", since such tests measure soil responses instead of soil properties. According to the theory, an in situ test should be able to measure 36 responses, being

Figure 2. Example of DMT results

36 the (variable) coefficients linking the 6 stress components to the 6 strain components. One measurement is a very small fraction of 36. Two measurements are also a very small fraction, yet 100% more than one measurement.

4 DESIGN APPLICATIONS

4.1 Design using soil parameters In most cases the DMT is used to determine "commonly used" geotechnical design parameters, notably the undrained shear strength cu and the constrained modulus M. Comparisons carried out at various National Research Sites by international research groups (see Figs 3-4) have shown quite good agreement between the profiles of cu DMT and MDMT and the profiles determined by other tests.

Totani G. et. al. (2001). Use of the Flat Dilatometer Test (DMT) in geotechnical design

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• Calcular LM, NM # OM en base a la información recibida

• ¿Es PQR < 1.0 o PQR > 1.0 ?

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LM =UA − U-U- − V-

NM =U- − V-0´1-

OM = 34.7(UA − U-)

¿Es PQR < 1.0 o PQR > 1.0 ?13

p0 94 kPap1 235 kPau0 30 kPa presión hidrostáticas´v0 21,6 kPa presión efectiva vertical in situ

Id 2,20Kd 2,96Ed 4,89 MPa

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Ejercicio 3: repaso ensayo PMTM

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Ejercicio 3: repaso ensayo PMT

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• ¿Cuál de las presiones UZ , U[ , U\ hay que utilizar ?

Coef. Empuje en reposo N-Presión horizontal 0´+ - = N- 6 0´1 -

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z 8 mg 19 kN/m3p0 90 kPapf 190 kPapl 260 kPa

s´v0 152 kPaK0 0,59

Módulo 2 y 3 Práctica –ensayos in situ...2006/12/01 · Práctica –ensayos in situ (84.07)...

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