6585844969

Penetration testing in Bułgaria    esopt

G. Stefanoff & M. Bejkoff    State-of-the-art report

1* Geologie al b e o k-

g r o u n d

In the oourse of introduotion of the penetration metbods for testing the foun-dation soil in our praotioe it was started first with the statio penetro-meter* As we know it renders possibility for determining the strength oharacte-ristios of the soil in-situ of non-cohe-rent and loose soils in which oase tak-ing of indisturbed sample for laboratory testing is rather hampered and in some instanoes even impossible. In the People’8 Republic of Bułgaria suoh soils are enoountered mostly along the Black 8ea and the Danube river* In many oases these soils are so weak that in order to use them as foundation for oonstruotion purposes hydraulic filia should be oar-ried out with the aid of hydromonitors* The sand filia are also subjeot to testing with statio and reoently with dynaza-io pene tronie tera.

In the oonstruotion of many taillng dumpa and in the first place during the superstructure the penetrometers appear-ed ae the only most adeąuate devioe for testing the properties of the tailing mass*

The silty-sandy character of the Blaok sea bottom ia another wide field for ap-plioation of the penetrometers*

Besides the oases pointed out, owing to the standarda elaborated for interpreta-tion of data from testing both of oohe-rent and no-ooherent soils, equally with statioal and dynamie penetrometers, these devices are applied almost at any plaoe, where the subaoil is not formed of rooks or very hard soils*

For laok of penetrometers in the past in many projects in Bułgaria the foundation soils have not been suffioiently studied or have not been studied at all* This oiroumstanoe most often leads to raising the cost of the foundation due to the over-seoured or not suffioiently seoured oonstruotion* The availability of statio and dynamio penetrometers gradually filie this gap in our researoh praotioe*

2*Desoription of penetrometers used in Bułgaria

2*1* Statio pene tronie ter

The statio penetrometers which are used in the People*s Republio of Bułgaria are with parametera in oomplianoe with the Bulgarian State Standard 8002-70 "Pounda-tions of buildings and Struotures* Statio penetrometers for testing foundation soil* General technical requirements^H • Acoording to this standard the statio pene tronie ter should oomprise the follow-ing parta s

-    penetration oolumn consisting of oon-ioal tip and hollow rod-pipes,

-    measuring system whioh should render possibility for separata reading of the tip resi8tanoe and the skin friotion or the total soil resistanoe,

-    an applianoe for driving the penetration oolumn in the soil*

The tip should be a Steel o one with a cross seotion of 10 omr ( d = 35,7 mm) and 60° angle at the tip, whlle the rod pipes whioh at the lower and hołd the drilllng tip should have eztemal dia-meter also d = 35,7 mm* The internal di ame ter of the rods should seoure the neoessary oonneotion between the o one and the measuring system at whioh the tip resistanoe or the oone is reoorded*

The Bulgarian State Standard 8002-70 al-lows for deviation from the values pointed out for the cone and rod dia-aeter - 0,3 mm, but the deviations of the cone and rods should be equal* Ao-oording to the same standard the measur-ing system should allow for independent measurement of the tip resistanoe and the skin friotion* The error of the peak resistanoe measurement should not exoeed 20% of the value measured and not morę than 10 Jq>/omr and the error of the skin friotion measurement should not exoeed 10% of the value measured*

The driving applianoe may be of diffe-rent oonstruotion allowing for penetration of the oolumn in the soil with a speed from 20 to 40 om/min*

Under the oonditions in Bułgaria as first and most appropriate pene tronie ter was oho sen a oonstruotion of Dutoh-Bel-gium type whioh was used in the State Geoteohnloal Institute in Gent - Belgiom. In our oonstruotion as a souroe of pres-sure foroe i na te ad of hand jaok we in-troduoed hydraulio Jack from "Tatra** truok* Its working stroke of 1*08 m oon-eiderably faoilitates the operation with statio penetrometer*

Sinoe the manuał drive of the hydra ulio pump was not easy the heavy physioal labour was soon replaoed by an internal oombustion engine* At the same time operation was adopted with simultaneous non-interrupted oourse of the rods and tip* The reading of the tip resistanoe and the total resistanoe is oarried out simultaneously on the manometers of the two separate oil ohambers*

The internal di ame ter of the oil ohambers is o ho sen 11*3 cm so that the piston to be preoisely 100 om²* Thus the reading in atmospheres is easily oon-verted into tona and in newtons respeo-tively* Reading of two manometers was adopted both for the tip and total re-