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Penetration testing in Netherlands    esopt

W.J. Heijnen    State-of-the-art report

The atatic penetration is in use in the Netherlands sińce 1930. Soil conditions are very favour-able for the application of this type of test. Results are mainly used for the estimation of the bearing capacity of piles_r but they also furnish information with regard to the ccmposition of the foundation soil.

The State of the art report gives a review of the application of the dutch cone test in the Netherlands.

1. IOTRODUCTION

The static penetration test is employed in the Netherlands sińce 1930. Prandtl's theory on the penetration resistance of a wedge shaped body into a soil mass is to be considered as the theoretical background of this method.

For a cone shaped body of smali size Keverling Buisoan assumed that the penetration resistance is governed by the following eąuation which is practically identical to the bearing capacity formula for a smali strip foundation at the surface of a soil mass.

%_c = ^Vb ■ ^pb ⁺ Vć • ^{c    (,)}

The bearing capacity coefficients and are functions of the angle of internal frictión of the soil.

It is not possible to derive theoretical values for these coefficients. Its relation has to be established by laboratory tests.

The penetration resistance of the cone depends also on the compressibility of the soil.

Frora simplified calculation regarding this phe-nomena Keverling Buisman established the following approximate relation:

q_cc * 2/3 E    (2)

The penetration resistance caused by pure com-pression of the soil skeleton is to be considered as an upper limit for the ultimate penetration resistance q^_c of the cone.

Within certain limits with respect to the diameter of the cone shaped body the penetration resistance only depends slightly on the size of the cone. Therefore the results of a penetration test may be extrapolated to the larger pile toe diameters.

The above considerations also hołd for the case of a penetration test below the surface of a soil mass.

This leads to the conclusion that an analogy ex-ists between a penetration test with a smali size diameter cone and a pile at the moment of failure. Therefore a sounding may be considered as model pile test.

In the case of a homogeneous soil the results of the penetration test, further referred to as the "dutch cone test" can be applied directly for the calculation of the ultimate bearing capacity of a pile toe.

It is obvious that the assumption of a homogeneous soil is not applicable for most cases of pile foundations.

On the contrary, a soil profile is normally com-posed of layers of different soil types. These layers vary in thickness and strength consider-ably.

In conseąuence of this the results of the sounding tests have to be transformed by means of model rules into bearing capacity values for a pile toe.

In the Netherlands this is normally done by a simple computation method which is based on the conformity of the slip linę patterns in the soil around the cone and the pile-toe.

The method was adjusted empirically by comparing the results of the calculations with special pile load tests.

Soil conditions in the Netherlands are very favourable for the application of static penetration tests.

Consequently this testing method is employed on a large scalę throughout the country.

Each year approximately 30,000 soundings are ex-ecuted by several soil mechanical consulting firms.

Its application is not restricted to pile foundation only but it is also used in connection with tests on undisturbed soil samples in the laboratory, for the prediction of the behaviour of shallow foundations, earth and road works and other structures.

The application of dynamie penetration tests in the Netherlands is restricted to a very few special cases.

Therefore no reference to this type of test will be madę in this report.

2.    SOIL CONDITIONS

In generał the Netherlands can be divided in two regions with respect to soil condition.

In the western and northern region a sand stratum of pliocene origin is covered by alluvial de-posits consisting of soft clay and peat layers. The thickness of this deposit varies from a few metres to 15 m and morę.

In the eastern and Southern region the sand stratum reaches to the soil surface.

It is obuious that this geological condition is very suitable for the application of the dutch sounding method.

With normal sounding equipment sufficient penetration can be obtained in order to get adequate information for the design of deep foundations.

3.    PENETRCMETERS USED IN THE NETHERLANDS

Since the first application of the dutch cone test in the field no revolutionary development has taken place with respect to either the method or the test procedurę.

In principal the method consists of pressing down into the soil a Steel cone shaped element with a top angle of 60° and a base-area of 10^ rem2.

Originally this was done by means of rods that can be moved free from the soil inside the so-called sounding tubes (see figurę 1).

The force needed for the penetration of the cone into the soil was measured at the surface by means of a roanometer on an oil pressure celi.

Normally these measurements were taken at inter-vals of 0.2 m downwards.

Cone and sounding tubes were pressed down either directly by hand or with a simple manuały operat-ed sounding press.