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Application and tentative validation of soil behavior
classification chart based on drilling parameter
measurements
Philippe Reiffsteck, Jean Benoit, Matthieu Hamel, Jean-Michel Vaillant
To cite this version:
Philippe Reiffsteck, Jean Benoit, Matthieu Hamel, Jean-Michel Vaillant. Application and tentative validation of soil behavior classification chart based on drilling parameter measurements. ISC’5, 5th international Conference on Geotechnical and Geophysical Site characterisation, Sep 2016, GOLD COAST, Australia. 6 p. �hal-01589854�
1 INTRODUCTION
Correlations of in situ test results with results obtained in the laboratory on test specimens from disturbed and intact samples has helped improving various empirical relationships between field and laboratory properties. However, it would be misleading to say that values de-rived from in situ testing can fully substitute values from laboratory tests. It is difficult to integrate certain aspects of soil behavior such as overconsolidation and effect of fines into these field correlations. However, it has become an increasingly important tool for the prac-titioner to check the consistency and variability of re-sults in the field.
Recently, the French national applications documents of Eurocode 7 for the design of shallow and deep founda-tions proposed using a classification chart based on the results of pressuremeter tests: limit pressure and Menard modulus. Similar to the soil classification de-veloped by Robertson (1990) for the static cone pene-tration test, this tool defines soil classes in a log-log plot using the normalized limit pressure versus the ratio of limit pressure to pressuremeter modulus. A similar approach has been taken and is presented in this paper whereas different drilling parameters are combined and normalized to define similar graphs to those proposed by Robertson (1990) in an effort to develop classifica-tion charts based on drilling measurements.
1.1 Classification and CPT
Following Schmertmann (1978), Douglas and Olsen (1981) and Parez and Fauriel (1988), Robertson sug-gested in 1990, a chart based on the normalized cone penetration resistance, Qt, and the normalized friction
ratio, Fr. These charts have been adopted by
practition-ers as they provide a "reliable" soil classification using the CPT and minimizes the need for sampling. The graph shown in Figure 1 is divided into zones that allow
soil classification according to particle size. The zones reflect the expected behavior of the soils within each zone rather than strictly based on grain size. The zones show a gradual transition from fine soil behavior to that of coarse soil. These two CPT normalized parameters are in fact compounds parameters specific to cone pene-tration.
The 1990 chart from Robertson is an improved version of the initial chart because of the normalization to in situ vertical stresses.
v v t ' -q = t Q (1) 100% v t s r q f F (2)
considering that qt qc(1a)u2 where a is the area ratio correction.
a) Ic= 1,31 Ic= 1,31 Ic= 2,05 Ic= 2,05 Ic= 2,6 Ic= 2,6 Ic= 2,95 Ic= 2,95 Ic= 3,6 Ic= 3,6 1 10 100 1000 0,1 1 10 N o rm a li ze d c o n e r e s is ta n c e Q t
Normalized frition ratio Fr Robertson (1990)
organic soils clayey soils silty soils sandy soils gravelly soils overconsolidated and cemented soils 7 6 5 8 9 3 2 1 4
Application and tentative validation of soil behavior classification chart
based on drilling parameter measurements
P. Reiffsteck
IFSTTAR, Marne la Vallée, Ile-de-France, France
J. Benoît
University of New Hampshire, Durham, New Hampshire, USA
M. Hamel
Fondasol, Cesson, Ile-de-France, France
J.-M. Vaillant
Fondasol, Enghein, Hainaut, Belgique
ABSTRACT: This paper presents an approach for developing a soil classification chart based on drilling pa-rameters. Tentative validation by comparison with a database of these tests leads to conclude on the reliability of the chart and proposes some suggestions for its practical use. A newer and preliminary version taking into account initial stress state of the ground is also presented.
b) 10 3,3 3,3 3 3 2,6 2,6 2,3 2,3 2 2 1,6 100 100 1000 1000 1000 3,6 3,6 1 10 100 1000 0,1 1 p*LM/p0 a pressuremeter chart [ log a/ log p*LM/p0 ]
clay sand silt chalk gravel
Sands & gravels Marl and marly
limestone fissured and wheatered rocks clays & silts
Figure 1. Classification charts (according to Robertson, 1990 and 2009) and chart based on pressuremeter results from current data sets
With
1. Sensitive fine-grained; 2. Clay - organic soil; 3. Clays: clay to silty clay; 4. Silt mixtures: clayey silt & silty clay;
5. Sand mixtures: silty sand to sandy silt;
6. Sands: clean sands to silty sands;
7. Dense sand to gravelly sand;
8. Stiff sand to clayey sand; 9. Stiff fine-grained.
In 2009, Robertson included the index Ic proposed by
Jefferies and Been (2006), which resulted in the circular arcs shown as thick lines in Figure 1a. The index Ic is defined as follows:
2
0,5 r 2 t c = (3.47+log(Q ) +(1.22-log(F )) I (3)The limit between the clayey behavior and sandy be-havior is given for Ic = 2.60.
Figure 1 also shows a dataset from experimental sites where quality PMT, CPT, SPT, FVT tests were con-ducted but in different geological and geographical conditions and locations. The classifications were done using soil descriptions from core drilling and laboratory test specimens.
1.2 Classification using Ménard pressuremeter test Similar to the classification of soils developed from the results of static cone penetration tests, we can envision creating a chart based on soil types and sizes on a graph of standardized limit pressure and the ratio of limit pressure to pressuremeter modulus. The log-log chart proposed by Baud (2005) and Baud and Gambin (2011,
2012), looks promising although the comparison of dif-ferent classifications does not allow to define clear dis-jointed unique areas (Reiffsteck et al., 2013). These same authors proposed a more elaborate version taking into account the initial state of the soil, whose im-portance is known, but it did not solve the problems of inadequate discrimination between soils inherent in this chart. The normalized pressuremeter based chart is shown in Figure 1b and compared to Figure 1a. It shows an average sensitivity of the five soil classes based on data from the experimental sites database. Fi-ne soils are located at the bottom left of the graph and granular soils in the upper right, with the intermediate soils in a central position.
Consequently, the use of curves defining a classification index Ic seems suitable for delimiting these areas. This
index could have the same threshold value of 2.6, sepa-rating the granular and coherent behavior as proposed by Jefferies and Been (2006), but with an opposite de-velopment (1.3 for clays and 3.6 gravel).
0,5 2 2 0 * PMT c p +(1,22-log( )) p log + (1 = I LM a (4)
This chart shows promises in its ability to classify soils where soils are firm (stiff soil, soft rock) and when hav-ing tests with Ménard modulus measured with minimal remoulding of borehole walls and unrestricted by the ar-tificial limit of 5 MPa as defined in the test standard.
2 CLASSIFICATION BASED ON MWD
Conception of a soil classification based on parameters recorded during drilling (VA: penetration rate; PE: net
thrust pressure; Pi: injection pressure; Qi: Drilling fluid
flow; Cr: torque; Vr: rotation speed - italicized are those
which are not usually measured) was attempted by many authors (Girard, 1985; Bourget and Rat, 1995; Ferry, 1996; Colosimo, 1998; Gui et al, 1999; Moussoutheguy, 2002). However, the combination of several compounds parameters with weighting methods and thresholds have not led to a fully reliable method of identification.
Figure 2 shows a graph of penetration resistance (Rp)
and modified Somerton index (Sd) for different soil
types and rock. It can be seen that compact clay and marl give large range of values of penetration resistance and does not allow discriminating between the two ma-terials without direct identification of the cuttings. The distinction between clays and marl is mainly based on the content of CaCO3.
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 0 1 2 3 4 5 6 7 s /0 ,2 m soil 0 5 10 15 20 25 30 35 0 1 2 3 4 5 6 7 PE /√ (VA ) soil
Figure 2. Relationship between the classification and the penetra-tion resistance or modified Somerton index (clay = 1, silt = 2, sand = 3, gravel = 4, chalk = 5, marl = 6, rock = 7)
a) 0 1 2 3 4 5 6 7 8 9 1 10 100 1000 10000 100000 p l (M P a ) s/0,2m clay silt sand gravel chalk marl rock b) 0 5 10 15 20 25 30 35 Frequency ratio (s/0,2m)/pl clay silt sand gravel chalk marl rock c) 0 1 2 3 4 5 6 7 8 9 0 10 20 30 40 p l (M P a ) PE/√ (VA) clay silt sand gravel chalk marl rock d) 0 5 10 15 20 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Frequency ratio 10.pl/(PE/√Va) clay silt sand gravel chalk marl rock
Figure 3. Relationship and histograms of relations between the pressuremeter limit pressure and various compounds parameters
The French national application document of Eurocode 7 for design of shallow foundation NF P94-261 provides in its Appendix A a preliminary soil clas-sification based on ranges of values from two drilling parameters, the penetration resistance Rp and modified Somerton index Sd (Figure 3) which consistently show good differentiation between soil and rock types. These two parameters are defined as follows:
m s 2 . 0 Rp and A E V P d S (bar/(m/h)-0.5) (5) Table 1 — classification of soils according to in situ testing and Rp
and Sd soil classes pl* (MPa) qc (MPa) N(1,60) Su (kPa) Rp Sd clays and silts very soft to soft < 0.4 < 1.0 < 75 < 45 < 2.5 firm 0.4 - 1.2 1.0 - 2.5 75 - 150 45 -138 2.5 - 8 stiff 1.2 - 2 2.5 - 4.0 150 - 300 138 -2308 - 13 very stiff ≥ 2 ≥ 4.0 ≥ 300 ≥ 230 ≥ 13 intermediate soils (silty sands, clay-ey sands, sandy clay) Classification according to figure 1 sands and gravels very loose < 0.2 < 1.5 < 3 < 27 < 1.3 loose 0.2 - 0.5 1.5 - 4 3 - 8 27 - 70 1.3 - 3.3 medium dense 0.5 - 1 4 - 10 8 - 25 70 - 140 3.3 - 6.6 dense 1 - 2 10 - 20 25 - 42 140 - 277 6.6 - 13 very dense > 2 > 20 42 - 58 > 277 > 13 chalks soft < 0.7 < 5 < 64 < 7 weathered 0.7 - 3 5 - 15 64 - 272 7 - 30 sound ≥ 3 ≥15 > 272 > 30 marls & limestones soft < 1 < 5 < 1100 < 6 stiff 1 - 4 5 - 15 1100 - 4400 6 - 26 very stiff > 4 >15 > 4400 >26 rocks weathered 2.5 - 4 4750-7600 50-80 Fragmented > 4 >7600 >80
Similar relationships to those proposed by Robertson (1990) can be developed for characterizing soils and rocks from the information obtained during the penetra-tion of a drilling tool. However, in order to normalize the net thrust pressure it must be divided by the penetra-tion rate (speed) in order to be constant as during pene-tration in CPT testing. The units have also been modi-fied to be in meters per second for penetration and rotational speed. v A v E V P ' Qt MWD (6) ation speed 100% C /V 100% torque/rot F R R r MWD A v E A v E V P V P (7)
To use the expression in Equation 7, the rotation pressure must be converted into torque. This requires knowing the capacity of the machine rotary motor (cm3/rev). 2 CR PCR cylindercapacity (8)
Similarly the rotational speed which is an angular velocity must be expressed in linear speed at the pe-riphery of the tool.
30
VRr (9)
A first calibration was performed on the IFSTTAR database (Figure 4) which unfortunately does not com-pletely cover the experimental sites used on the two graphs in Figure 1. 1,31 1,31 2,05 2,05 2,6 2,6 3,5 3,5 5 5 0,0001 0,001 0,01 0,1 1 10 100 1000 0,01 0,1 1 10 100 1000 Nor m al iz ed p en et ra ti on r es is ta n ce Qt M W D
Normalized friction resistance Fr MWD
clayey soils silty soils sandy soils gravelly soils chalky soils marly soils rocks
Figure 4. Classification chart based on the proposed drilling pa-rameters with sites data set
Figure 4 shows that stiff soils and rocks are located in the lower right part, granular soils are in an approxi-mate central position and clay soils are spread over the entire range. At this time, the influence of over-consolidation or cementation of clays has not been completed. Similarly, soils classified as clayey or sandy are mostly intermediate soils with this second classifi-cation not yet defined.
An attempt to introduce a classification index to re-fine the soil classes is shown in Equation 10 and repre-sented in the graphs of Figures 4 and 5.
2
0,5 MWD r 2 MWD c (3.47+log +(1.22 log( )) I QtMWD F (10)The chart has been tested with a database collected by Fondasol using their project data (Hamel and Vaillant, 2014). It has 18 sites mainly in the Paris re-gion and around 100 boreholes from 15 to 30 m deep, leading to 121,730 values (Figure 5).
It can be observed, in spite of the dispersion associ-ated with the inherent variability of tested geologic ma-terials, the test procedures and the potential classifica-tion errors or other approximaclassifica-tions, a fair posiclassifica-tioning of classes of soils on parallel axes going from (1; 10) to (1000 ; 0.01).
The clay materials are situated on an Fr MWD zone =
10 and Qt MWD ranging from 0.1 to 1. The marly clays
are found closer to hard soils as they are similar to cal-careous marl. The percentage of limestone is indeed not defined (Ic MWD > 5).
Granular materials are along high values of Fr MWD
for Qt MWD close to unity. Some of the silt is also located
on this part of the diagram (Ic MWD ≅ 5).
Indurated materials such as limestone, calcareous marl and marl are positioned on two lines: a high line ((1; 10) (1000, 0.01)) and a low line ((1; 0.02) (100; 0.001)). The cluster of points for calcareous marl, marly clay and limestone are located in an area where Fr MWD
= 1 and Qt MWD varying between 1 and 10 (Ic MWD <3.5).
Figure 5. Classification chart based on the proposed drilling pa-rameters with the dataset of sites provided by Fondasol
3 CONCLUSIONS
Drilling parameters measurements or instant logging parameters have greatly improved the quality of
drill-ing. The use of the recorded drilling parameters has been used in this paper to suggest a new application to classify soil using a classification chart similar to what Robertson proposed for the CPT. However, the results obtained to date can not be used as is for the following reasons:
- Greater data variation than for the CPT and the pressuremeter,
- Heterogeneity of the drilling machines used to de-velop the database,
- Possible interrelationship of the various parameters and factors influencing the recorded responses.
Identification and classification of soil and rock is normally a matter of EN ISO 14688-1 and EN 14688-2 and also the 14689-1 standards. The idea is to use in combination the information from these techniques with those of conventional reconnaissance (sampling, pene-tration or expansion tests), to improve the image of the subsurface and better manage the overall risk generat-ing a geotechnical model of the site richer qualitatively and quantitatively.
4 ACKNOWLEDGEMENTS
The authors thank P. Sauvage and B. Tcherniawsky for the information they were able to provide them on the drilling machines used in this study.
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