Correlations between soil parameters and penetration testing results

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1 1 A 1 6 Correlations between soil parameters and penetration testing results Corrélation entre paramètres du sol et résultats de sondage J. FORMAZIN, Director, VEB SBK Wasserbau, KB Baugrund Berlin, Berlin, GDR H. HAUSNER, Research Engineer, VEB SBK Wasserbau, KB Baugrund Berlin, Berlin, GDR SYNOPSIS The article deals with determining in situ soil parameters by means of sounding. The established correlations frequently allow for quickly and reliably finding parameters necessary for designing foundations. INTRODUCTION Penetration testing procedures are providing a host of information about soil properties which have replaced expensive and time consuming drilling and laboratory testing in various cases in recent years. Penetration testing procedures were successfully used in such cases as: Determination of parameters (CPT, L R S, SRS) - Classification - Layer demarcation - Bearing capacity of piles - Drivability - Compaction tests - Tests of homogeneity - Determination of cavities (CPT) (CPT, SRS) (SRS) (SRS) The following chapters will deal with establishing correlations between soil parameters and sounding results. The number of blows per 10 centimetres penen tration is considered a parameter (LRS: SRS: N 1 q ). Cone penetrometers - Cone penetrometer DS-10 (Pushing force 100 kn) - Cone penetrometer DS-20 (Pushing force 200 kn) 1 0 ' The parameters of the cone penetrometers are adapted to international standards (Tokyo 1977). Parameters are q and f, x s PARAMETERS OF COHESIONLESS SOILS Density index The density index 1^ is determined in the following way, irrespective of the depth: SOUNDING DEVICES CPT: ID = ^D (qc > The following devices were used in subgrade investigation: LRS: ID = ID o rh c SRS: ID = ID (N l0 ) Dynamic penetrometers - Light dynamic penetrometer Mass of hammer: 10 kg Height of fall: 50 cm - Heavy dynamic penetrometer Mass of hammer: 50 kg Height of fall: 50 cm LRS SRS These functions are valid for depths > > 1.5 m (LRS) and 2.0 m (CPT, SRS) respectively, There are also functions depending on the depth. Figure 1 shows the relation between cone resistance and density index, respectively and depth

= C (q ) z z c ' for foundations with a base of A S 10 m 2 and static soil pressure d * 50 kn m2.

2 1AI 6 e o. 01 a Cone resistance qc in MN m 2-2D Poorly graded sands and gravels Normally graded sands Modulus of dynamic subqrade reaction Figure 7 shows the function C = C (q ) z z c ' for foundations with a base of A S 10 m 2 and static soil pressure d * 50 kn m2. 2 Values for Cz with A < 10 m are to multiplied by the factor and for ^stat "* knm2 they are to be multiplied by the factor 1 Density index versus cone resistance of cone penetrometer and sounding depth I I ^stat If 50 knm2 Degree of compaction Requirements for compaction are often given as a degree of compaction (quotient of dry bulk density and standard density). Figure 2 shows the plot of the function Allowable soil pressure (recommended value) Figure 8: d = d (n io^ D rivability ZS = XS «c > Figure 9: R = R Bulk density Figure 3 shows the plot of g = g (qc ) Modulus of deformation Figure 4: Eq = Eq (qc ) Effective angle of internal friction Figure 5: cp = (n1 Q ) Critical vibratory velocity Data on the critical velocity (i. e. the v e locity at which compaction by vibration starts under given conditions i. e. the stability of the cohesionless soil is lost), are important for foundations of dynamic structures, such as foundations for machines. Figure 6 shows the function 2 Degree of compaction of poorly graded sands and gravels versus cone resistance of cone penetrometer 4 6 0

1AI 6 Cone resistance qc in MNm2 Bulk density of poorly graded sands and gravels versus cone resistance of cone penetrometer 5 Effective angle of internal friction of poorly graded sands versus

5 m) SP, GP In stationary excited y vcrit instat Stationary excited vcrit stat Coarse sand, gravel Medium sand (3) Fine sand... 1.

3 1AI 6 Cone resistance qc in MNm2 Bulk density of poorly graded sands and gravels versus cone resistance of cone penetrometer 5 Effective angle of internal friction of poorly graded sands versus number of blows of light dynamic penetrometer (Range of application: Depths > 1.5 m) SP, GP In stationary excited y vcrit instat Stationary excited vcrit stat Coarse sand, gravel Medium sand (3) Fine sand Cone resistance qc in MNm Cone resistance qc in MNm2 Modulus of deformation of Holocene, Pleistocene and Tertiary sands and gravels versus cone resistance of cone penetrometer (Depth: 2 m) 6 Critical vibratory velocity of poorly graded sands and gravels which ware excited stationary and instationary by machine foundations versus cone resistance of cone penet rometer 4 6 1

1 A 1 6 o > Q Cone resistance qc in MNm2 Modulus of dynamic subgrade reaction of sands versus cone resistance of cone penetrometer 9 Drivability of poorly graded sands and gravels versus number of

the following values for boulder clay were found in the Berlin area: 2 Cone resistance in MNm Consistency 0.5 to 1.4 very soft 1.4 to 2.5 so ft 2.5 to 4.9 stiff > 4.

4 1 A 1 6 o > Q Cone resistance qc in MNm2 Modulus of dynamic subgrade reaction of sands versus cone resistance of cone penetrometer 9 Drivability of poorly graded sands and gravels versus number of blows of heavy dynamic penetrometer PARAMETERS OF COHESIVE SOILS Consistency index There are correlations between the consistency index and the cone resistance, e. g. the following values for boulder clay were found in the Berlin area: 2 Cone resistance in MNm Consistency 0.5 to 1.4 very soft 1.4 to 2.5 so ft 2.5 to 4.9 stiff > 4.9 very stiff Modulus of deformation The modulus of deformation E o of soft to stiff plastic silts and clays can be given as an approximate linear function of the cone resistance q c of the cone penetrometer: Number of blows n o = F The factor F depends on the natural void ratio as follows: c Allowable soil pressures for ver- ^or en = : F = 3 '~ tically loaded strip foundation on poorly graded sands 'or en = 0.60 : F ~ 7,

1AI 6 Undrained shear strength With water saturated, highly to extremely cohesive normally consolidated soils there is the following approximate relation between the undrained shear strength cu and

CORRELATIONS BETWEEN THE RESULTS OF THE DIFFERENT PENETROMETERS - Correlations are to be considered evaluations in the case of cohesive soils.

5 1AI 6 Undrained shear strength With water saturated, highly to extremely cohesive normally consolidated soils there is the following approximate relation between the undrained shear strength cu and cone resistance q c of the cone penetrometer: ^ c cu 15 This relation is valid for an apparent angle of internal friction < u = 0. CORRELATIONS BETWEEN THE RESULTS OF THE DIFFERENT PENETROMETERS - Correlations are to be considered evaluations in the case of cohesive soils. - Further studies should first of all make correlations more precise and find correlations between the results of penetration testing results and directly measured soil parameters, respectively, in particular for cohesive soils. REFERENCES Technological instructions in the field of penetration testing at VEB SBK Wasserbau - KB Baugrund Berlin - (unpublished) There are correlations between the parameters q n 1Q and so that any comparisons can be made. Since internationally SPT results are often referred to, we give a graphic representation of the results for dynamic penetrometers SRS and LRS-1050 respectively and the SPT penetrometer ( 10). n10 - IRS 10 Relation between number of blows n1q, N 1(j and N 3 0 for sands CONCLUSIONS - Correlations between penetration testing results and directly measured soil parameters present data about the subgrade quickly and economically. - Correlations give reliable results for cohesionless soils

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