SITE INVESTIGATION REPORT

DYNAMIC CONE PENETRATION TEST REPORT ROBERTHA Sekyiwa NKRUMAH 10353092 SITE INVESTIGATION REPORT2014

TABLE OF CONTENTCHAPTER ONEINTRODUCTION.. 2CHAPTER TWOBACKGROUND STUDY..... 3CHAPTER THREE METHODOLOGY..4-5CHAPTER FOURRESULTS . 6-7CHAPTER FIVE BEARING CAPACITY ANALYSIS 8CHAPTER SIX CONCLUSION .. 9

1.0 INTRODUCTION1.1 GENERAL This report presents the outcome of the site investigation carried out for the proposed construction site at University of Ghana, Earth Science Department. Ms Robertha S. Nkrumah and her team from Legon Geotechnical Consultant Inc carried out the site investigation on the propose site of the University of Ghana, Earth Science Department. This report provides detailed geological and engineering properties of the proposed site from the tests carried out on the site.1.2 PURPOSE AND SCOPE Investigation of the underground conditions at a site is prerequisite to the economical design of the substructure elements. In general, the purpose of this site investigation was to provide the following: Information to determine the type of foundation required (shallow or deep). Information to allow the geotechnical consultant to make a recommendation on the allowable bearing capacity of the soil. The Dynamic Cone Penetration Test was carried out to achieve the above purpose.

2.0 BACKGROUND STUDY2.1 GEOLOGY AND Rocks of the University of Ghana, Legon are of the Togo structural unit. These are stronglytectonised phyllite, quartzite and serpentinite. The weathered top soil is mainly laterite. 2.2 SEISMICITYHistorical seismicity of southern Ghana shows earthquake events recorded as far back as 1862.The probable causative faults being the Akwapim Fault Zone and the Coastal Boundary Fault. The event with the highest magnitude of 6.5 occurred on 22nd June 1939. It affected most of West Africa and the approximate location of the epicenter was SSE of Accra, about 40km out of sea. The Legon area receives minor shocks during such an event.2.3 OTHER FEATURESThe area is a highly built place with a lot of buildings most of which are more than 30yrs old. Drainage in the area is very good. First class and second class roads surround the area with tall trees along the principal streets.

3.0 METHODOLOGYWe began our investigation by looking out for information on the site. During the desk study, we obtained information about the proposed site from the internet, the Geological Survey Department of Ghana records, topographical maps, and soil research data. After the study, we had information about geology and seismicity of the area as described in Chapter one. We also had an idea of the topography, vegetation and drainage of the area.We then proceeded with a visual inspection of the site to confirm the reality on the ground with respect to drainage topography, present and past land use, groundwater levels from nearby wells and constructions works around the area.We proceeded with the dynamic cone penetration test on the site.3.1 DYNAMIC CONE PENETRATION TEST (DCPT).Cone penetrometer is a versatile tool for soil exploration. The equipment comprise of a cylindrical cone as the tip with a metal rod screwed to it. a The dynamic penetrations is defined as the number of blows per 10 cm penetration are plotted as a function of depth on the pion jar drill hole logs. The dynamic penetrometer testing is terminated where there is an obvious refusal i.e., where the dynamic penetration r exceeds 100 counts. The procedure in getting the dynamic penetration is at follows; After examining the site, we chose three points on the site where the tests will be carried out in a triangular format The metal rod was marked every 10cm so the number of blows per 10cm can be counted effectively. Each rod is about 100cm. The hammer and anvil are put in place as in fig1 below. Then the hammer is then lifted and dropped on the anvil to advance the rod into the ground. The number of blows required for the rod to penetrate 10cm in the soil is counted and recorded on the log sheet as shown in table 1 below. After 100cm without refusal another 100cm rod is added still refusal. At refusal the process is stopped and the process is repeated at the next selected point. fig 1. DCP tool in operation4.0 RESULTSDEPTH (cm)hole Ahole Bhole C

10721

201411

301711

401011

501912

603221

7035010

803059

90931414

1002617

11028

12032

13031

14067

15073

16044

17041

18028

19027

20036

21052

22033

23028

24033

25035

26033

27050

28058

29083

300100

Table 1 DCPT values for the three holes A graph of the numberof blows per 10cm against depth was prepared shown in graph 1 and graph 2 below.

Graph 1 a graph of depth against number of blows per 10cm (r) for hole A and B

5.0 BEARING CAPACITY ANALYSISThe allowable bearing capacity of each hole was approximated as Qall = 30 r where r is the number of blows required to advance the cone by 10 cm.Hole AAt 90cm below the surface; r = 90; Qall =30rQall = 30*93 = 2790 kPaHole BAt 100cm below the surface; r =26Qall = 30*26 = 780 kPaHole CAt 300cm (3m) below the surface; r =100Qall = 30*100 = 3000 kPa

The bearing capacity of the soil increases with depth. At 3m below surface the allowable bearing capacity was 3000 kPa. For example; a square foundation with dimension 3*3m, the allowable bearing load will be 27000kN. A knowledge of the allowable bearing capacity will help in designing a foundation that will be able to bear a design load. The soil at the site it laterite. Various buildings are around the site, most of which have shallow foundations. A new construction work is ongoing near the site. This two-storey building with a basement is sitting on a deep foundation.

6.0 CONCLUSIONAt 3m below the ground surface the allowable bearing capacity at the site is 3000kpa. The bearing capacity of the area increases with increasing depth. The soil will be able to support shallow foundations, but for high rise buildings, a deep foundation to the bedrock is more preferable. Judging by the long life span of other buildings near the site, the soil is able to support structures put on it. Nevertheless, more test must be carried out to know some properties of the soil and groundwater characteristics of the site for a complete evaluation of the bearing capacity of the ground.

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