1. Hussein H. Karim1, Imzahim A. Alwan2, and Fatima Assad Tayeb3
The 2nd International Conference on Buildings, Construction and Environmental Engineering- BCEE2
17-18 October 2015
Beirut, Lebanon
Delineation Landfill Depth using 2D Electrical Resistivity Imaging (ERI) Technique in Kut City, Eastern Iraq
Hussein H. Karim1, Imzahim A. Alwan2, and Fatima Assad Tayeb3
1-D Resistivity Survey: Schlumberger array is used for resistivity sounding survey. The VES curves can be classified into two groups; the first involves 5 VES points consists of four geoelectrical layers of QH, KQ, QQ and QH. The second group appears three ngeoelectrical layers involving 9 VES points of Q type. Fig. 1 a and b shows resistivity curves for VES 29 and VES 31 as representative curves. The apparent resistivity sections show a decrease in apparent resistivity values with depth, and they give a primary picture about the distribution of deposits.
2–D Resistivity Surveys: The results of this survey study are also used to create 2D images with RES2DINV software. From the analysis of all sections, the maximum depth of investigation was about 34 m and resistivity values are ranging from 1 to more than1000 Ω.m. Fig. 2 shows the inverse models of 2D imaging for the parallel Lines 27 to 31as representative sections.
Fig. 3 shows of isoresistivity map of the landfill layer with values ranging between 30 to more than 170 Ω.m. While, Fig. 4 shows depth of the landfill layer with values ranging between 2 to 15 m. Maximum values of resistivity are concentrated in the NW and NE parts of the area, while minimum values are concentrated in SE of the area. The maximum values of landfill depth appear in NE and SW parts of the area and the minimum values are concentrated in the NW and SE parts of the study area.
1 Professor, Build. & Const. Eng. Dep., Univ. of Technology, Baghdad, Iraq. 2 Asst. Professor, Build. & Const.Eng. Dep., University of Technology, Baghdad, Iraq. ( 3 M.Sc. in Geomatics Engineering. (
Background
Surface geophysical methods afford quick, inexpensive and non- invasive means to help in characterization the subsurface geophysical formation. They provide information on subsurface properties, such as soil and landfill thickness, depth to bedrock, location and distribution of conductive fluids, and fracture zones and faults. However, there are numerous limitations to the information obtained by the geophysical techniques and they shall not be expected to provide reliable results under all circumstances. All geophysical information should be crossed-checked by borings and/or other direct methods of exploration. Electrical resistivity of the soil is considered as an indicator for the variation of soil properties. Electrical Resistivity Survey is carried out to determine the resistivity distribution of earth layers. Electrical current is injected to the ground and then potential difference is measured. This measured potential difference pattern provides information on the subsurface condition and electrical properties of the soil.
Objectives
The main objective of the present study is applying detailed 2D resistivity surveying in the site of investigation to delineate the depth of landfill by correlating resistivity data with geotechnical data taken from boring.
CONCLUSIONS
1. The landfill has been identified as the upper resistive feature (layer) consists of domestic wastes and broken fragments and is characterized by its low N-values.
2. The landfill layer appears at different depths from ground surface to a depth of 8 m and it was recognized with high resistivity ranging from 30 Ω.m to more than 1000 Ω.m.
3. The inversion sections also show a layer with medium resistivity (5-30 Ω.m) represents the clay and layer overlapping with layer by very low resistivity (˂ 5 Ω.m) that represents the silty clay.
4. The outputs interpretation is in agreement geotechnical data obtained from the borehole logs available in the site of the study.
5. The resistivity and depth contour maps show that the resistivity values are ranging between 30 to more than 170 Ω.m and the depth values are ranging between 2 to 15 m.
FIELD WORK
The aim of this work is to identify the landfill depth in the site for engineering purposes. ABEM Terrameter SAS 4000 was used for data collection of ERI. The total area of the site under investigation is about m2. Field work consists two parts, 1-D and 2-D surveys. For 1-D survey, 14 VES points shown in Figure 4 have been investigated along spreads of 50 to 100 m long by using Schlumberger array for sounding technique. For 2D imaging survey, 36 spreads with total length of 3304 m and different electrode spacing have been surveyed using Wenner-Schlumberger array for all spreads.
DATA INTERPRETATION
After the field survey, this step involved converting the apparent resistivity values into true resistivity (for 1-D) and into resistivity model section (for 2-D) that can be used for interpretation