1 DPL OPERATION PRINCIPLE

1.1 Traditional DPL

A DPL apparatus operates with a 10 kg weight, drop height 50 cm, generating the energy of 50 kJ to drive rods and cone to 12 meter depth. The cone, massive, of diameter d = 35.7 mm, tip angle 90º and cross section 10 cm², admits to capture resistance in-formation of the soil.

1.2 DPL NILSSON

The Brazilian modified DPL system, known as DPL NILSSON is an upgraded modification of the tradi-tional DPL, improved by torque measurements to register lateral cone friction. After every meter of penetration, before a new rod is connected, a torque test is made. The DPL NILSSON apparatus is non-motorized, easily dissembled in smaller parts, light and easy to transport and operates with high effi-ciency. One assembly staffed by 2 or 3 persons can advance 50 to 60 meters per day.

1.3 Comparisons

Compared with other field tests, DPL is light and easy to transport. The complete equipment weights less than 100 kg and can be transported in a small car. It is possible to install in small and narrow lo-cals, and is environment friendly. A great vantage obtained by the design is the clearly defined geome-try and constant mass which qualifies the cone as a discreet, measurable object. Different from a sam-pler, the DPL cone is massive and cannot contain air, water or soil, so objective resistant measure is possi-ble.

Figure 1. DPL NILSSON apparatus on campaign at Indaia-tuba/SP, Brazil.

Parameter approach from DPL test

Thomas Nilsson B.Sc. Civil Engineering, M.Sc., Brazil

www.nilsson.com.br

ABSTRACT: The article presents approaches and collections of geotechnical parameters from the port-able field test apparatus DPL NILSSON, manually operated by two persons. The raw parameters are ob-tained by blows and torque test. Some of the obtained geotechnic parameters for dimensioning are tip resis-tance, side friction, compacity and consistence. Significant vantages by this equipment is access to remote sites, high production, transport, low cost and positive ecological aspects..

Figure 2. Comparison in proportional scale between SPT-sampler, DPL cone and CPT-cone.

2 PRIMARY PARAMETERS

2.1 Obtained parameters

The prime raw parameter, obtained from any DPL test is N10 = blows to advance 10 cm. The DPL NILSSON test include torque on the assembled rods and cone. Mmax is the maximal obtained moment, captured instantly before soil rupture, and Mres is the average residual moment on the continuous rotation after rupture.

2.2 Tip resistance

The modified Hiley equation (Thomas Nilsson) gives:

21

22

11

2 mm

mem

ss

hgmakP

elpl

f+

⋅+⋅

+

⋅⋅⋅⋅= (1)

where Pf = tip force; k = correction factor to cover energy deviation, a = hidraulic correction factor, m1 = weight of hammer; m2 = weight of rods, anvil and cone; g = earth gravity; h = fall height of ham-mer; spl = plastic soil displacement; sel = elastic displacement of equipment and soil; e = coefficient of impact.

fA

Pq

c

f

c −= (2)

where qc = tip resistance of cone; Ac = cross section area; f = lateral resistance.

2.2 Lateral resistance

The vertical aligned surface of the cone has the same height as diameter, the nominal contact area with soil = 5πD2/4. For DPL NILSSON, the theoretic ob-tained area of soil contact, 50cm² should be in-

creased to 60cm², as the upper side of the cone has some soil contact. The lateral resistance is obtained by the equation.

LA

Mf

⋅= (3)

M = Moment, L = moment lever. A = Cone surface area in contact with soil The lever is d / 2 for the lateral section and d / √2 for the tip section. The resultant moment lever can be approached to 16mm. Approach the product AL to 100 (cm² x cm), f = 10M. moment in Nm, AL in m x m² and f in kPa.

The interface friction between the cone (steel to soil) is supposed to be less than the inner shear resis-tance of the soil so the received value of f can be used as a safe measure of soil shear resistance.

Figure 3. Raw parameters from DPL NILSSON test: Table and graph of blows N10, graph of lateral resistance f, and graph of tip resistance qc.

3 PROJECT PARAMETERS

3.1 Source

The parameters are acquired from necessary number of blows to penetrate a given distance, from neces-sary moment to rotate the cone and from soil and water print on extracted rods .

3.2 Cohesion and friction angle by DPL NILSSON

The shear resistance can be estimated by DPL side friction, as earlier shown. As expressed by Mohr, it is composed by cohesion and friction angle.

φστ tan'⋅+= cfu (4)

If the soil contains > 40 % clay, it can be considered as a cohesive soil. If > 75 % sand, it should be con-sidered as a friction soil. Joseph Bowles relates the interface friction angle be-tween metallic surface and soil δ = 14° to 22° for fine to coarse sand, and δ = 11° for silt. That is ap-proximately 15° less than the ordinary interior fric-tion angle of the soil. Suppose a torque test in clay, the shear resistance is mastered by cohesion. The cohesion of the soil should be higher than the measured lateral friction between the smooth cone surface and the surround-ing soil, so consider c > f. DPL test in sand is governed by the friction angle. Approaching cohesion to zero, the estimated friction angle can be expressed by the formulae:

'019.0 οϕ

⋅>

f (5)

where σ is the soil tension and f is the measured side friction.

3.3 Allowable load

The resistance value derived from pile driving for-mulas by Bolomey, 1974, gives the Dutch equation:

eAMsS

HMrd

⋅⋅+⋅

⋅=

)(

2

(6)

where M = weight of the hammer; S = weight of the extension rods; s = length of the extension rods; H = height of fall; A = cone cross section area; e = aver-age penetration/blow.

For DPL of standard dimension, this equation can be expressed as a second degree equation, with rd given as a function of the penetration of the driven rods:

102 )44,006,0003,0( Nssrd +⋅−⋅= (MPa) (7)

Table 1. Obtained values, applying the Dutch equation down to 5m. _________________ z rd m MPa _________________ 1 0.35N10 2 0.29N10 3 0.25N10 4 0.22N10 5 0.20N10 _________________

In “Procedimentos de Sondeos”, Jesus Puy Huarte, recommend the allowable load, for footings:

20d

adm

r=σ (8)

For piles:

612d

admd rr

<< σ (9)

4 APPROACHES FROM BLOWS N10

The blows of DPL NILSSON are presented in a graph with the horizontal x-axis graded up to 100 blows N10 , designed as function of depth. The end of DPL penetration, limited to 12 m, is also gov-erned by a maximum soil resistance corresponding to some 25-30 N of blows of SPT.

4.1 Blows vs. compacity

To evaluate the compacity of friction soils, the fol-lowing table gives an idea how to direct interpret DPL values: Table 2. Compacity of granular soils evaluated from DPL ___________________________ Blows Compacity N10 ___________________________ < 1 Very loose < 7 Loose 7 - 83 Medium > 83 Dense ___________________________

4.2 Blows vs. consistence

For classification of consistence in cohesive, unsatu-rated soils, with Plastic Index under medium value, the following table is extracted from the German standard DIN 4094.

Table 3. Consistence of fine soils evaluated from DPL ___________________________ Blows Consistence N10 ___________________________ < 3 Very soft 3 - 6 Soft 6 - 12 Medium 13 - 22 Stiff 23 - 45 Very stiff > 45 Hard ___________________________

A soil of N10 < 7 blows needs a special attention in the project, such as bypass with piles, reinforcement of the soil or other kind of geotechnical engineering solutions. Soils with N10 over 80 blows do generally have medium to high resistance.. Soils with N10 from 3 to 25 are normally easy to excavate.

5 CONCLUSIONS

The number of blows N10 of DPL allows quick ap-proaches of some soil characteristics like resistance, consistence and compacity. From torque tests in the apparatus DPL NILSSON, parameters as friction angle and cohesion can be roughly estimated.

In the choice between expensive and simple tech-nology, some equipments of simple technology gives a positive cost-benefit rate by low operation costs, high test velocity, easy transportation, access to dif-ficult locals and fast interpretation. The technical quality is rather a function of project, raw material and manufacturing than of complexity and hi-tech.

The service quality depends on compatibility with available labor, access, environment and control. Field campaigns are subjected to rude conditions and depend a lot on logistics. A portable equipment like DPL equipment fits good under such conditions.

6 REFERENCES

Bergdahl U., Ottoson E. 1988. Soil Characteristics from penetration test results, Proc ISOPT-1, Or-lando, USA. Bolomey, H 1974. Dynamic Penetration – Resis-tance Formulae. Proc European Symposium on Penetration Testing Vol 2:2, Stockholm 7p. Bolton,M 1979, A guide to soil mechanics, Macmillan Press, London, UK. Bowles, J.1986. Engineering Properties of Soils and Their Measurement Cunha, R, Nilsson. T. 2004. Advantages and equations for pile design in Brazil via DPL tests, ICS

2004, Porto/ Portugal, 20-25 de Setembro de 2004, 7p. DIN – Taschenbuch.1991. Erkundung und Unter-suchung des Baugrunds. Beuth Ireland, H.O. , Moretto, O and Vargas. M. The Dy-namic Penetration Test: A Standard that is not stan-dardized. Geotechnique, Vol 20, 7p ISSMFE 1989. International reference test proce-dures for dynamic probing (DP). Report of the ISS-MFE Technical Committee on Penetration Testing of Soils –TC 16 with Reference Test Procedures. Swedish Geotechnical Society, 49p. Jesus Puy Huarte. 1977. Procedimentos de Sondeos, teoría, práctica y aplicaciones. Publicaciones cienti-ficas de la Junta de Energia Nuclear, Madrid. 549p. Massarsch, R. , Lindholm, P, Mårtensson, O. 1976 . Ny lätt sonderingsmetod. (New Light Penetration testing Method). Royal Institute of Technology, JOB. Rep. No 3, Stockholm Moss, R.E.S., R.B. Seed and R.S. Olsen, "Normaliz-ing the CPT for Overburden Stress," Journal of Geo-technical and Geoenvironmental Engineering, American Society of Civil Engineers, doi:10.1061/(ASCE)1090-0241(2006)132:3(378), March 2006, Vol. 32, No. 3, 10p. Nilsson. T. 2000. Os ”Módulos” de Mecânica dos Solos, 32.d Pavement reunion, Brasilia/ DF. 4p. Nilsson. T. 2000. Ensaios para obtenção de ”Módu-los de Elasticidade”, 32.d Pavement reunion, Brasi-lia/ DF, 6p. Nilsson. T. 2003. Initial Experiences of DPL NILS-SON, I Central Brazilian Plateau Seminar. CD- ROM, 7p. Nilsson. T. 2004. Comparações entre DPL NILSSON e SPT, Geosul 2004, Curitiba/ PR, 20-23 de Maio de 2004, 6p. Nilsson. T. 2004. O penetrômetro portátil DPL NILSSON, SEFE V / BIC II 2004, São Paulo/ SP, 6p.

Triggs Jr. J.F., Liang R.Y.K. 1988. Development of and experiences from a light-weight, portable Penetrometer able to combine dynamic and static cone tests. Proc ISOPT-1, Orlando, USA.

Walter Rodatz. 1992. Grundbau, Bodenmechanik Unterirdisches Bauen. Institut für Grundbau und Bodenmechanik, Braunschweig, Germany. 345 p.