6585844982

Israei

190

Fig. 8 - Modulus of Subgrade Reaction

versus Relative Density

times discontinuous and the sampler fell freely after receiving a number of blows. These "free falls", of up to 60 era, were found especially where a hard thin layer was encountered. This behaviour indica-ted piąte formations with an einpty space or very loose sand layers in between. It is obvious that in such a case the SPT number by itself is meaningless.

In another site, both pressuremeter tests and SPT were performed and large varia-tions occurred in the blow counts from two adjacent borings only two meters apart. In one boring the N values ranged from 10 to 20 and in the other from 10 to 100 throughout a depth of 20 meters. Menard pressuremeter results in the boring with high blow counts showed Iow E_s values_r ranging from 0 to 120 kg/cm².

It is thought that the SPT results were influenced markedly by the presence of thin layers of sandstone and gravel, and did not properly measure the relative density of the sand and gravel.

The use of the standard penetration test as a tool for both the design and con-struction stages of fills under water may be illustrated by the following example.

At one of the Israeli ports an area was reclaimed by dumping a sand and gravel fili behind a sheet pile retaining wali.

The fili was a well-graded materiał ran*-ging from 100 percent finer than 6.3 cm to less than 10 per cent passing the 200-mesh sieve. Maximum dry density was 2130 kg/ra³ and minimum density was 1850 kg/m . The thickness of the fili varied from zero to eight meters. Design loa-dings on shallow foundations were expec-ted to be at least 1 kg/cm² and settle-ments could be critical. Existing dum-ped fili was tested by SPT methods to determine the original density, as placed and the changes after trying out several methods of improving the fili, such as:

a)    placing a surcharge of about 10 ton/ m² on the existing sand and gravel;

b)    compacting the surface of the sand and gravel with 20 passes of a heavy BOMAG vibratory roller, and

c)    using vibroflotation.

The original dumped fili, by interpre-tation of SPT values, had a relative density of about 45 per cent, except near the surface where construction traf-fic had produced dense conditions with a D_r indicated to be morę than 100 per cent

After placeroent of a test fili surcharge SPT results were obtained, as shown in Fig. 9.

No oł Blows S.P. T Ń 0    10 20 30 40 50 60 70

Fig. 9 - SPT Results as Influenced

by Test Fili

They are higher than original values be-cause of.the extra vertical pressure but did not indicate a large increase in the relative density of the deeper fili ma-terials. Measured settlement under the surcharge fili was found to average 6.6 cm of which 3.8 cm'occurred after