UNDRAINED SHEAR STRENGTH OF SELECTED SOILS IN HILLA CITY USING TORVANE DEVICE

This investigation is carried out to study the shear strength of soils using the new Torvane technical device in three selected sites in the studied area, which are Al-Thyala, Al-Bakaerly, and Street 80 in Hilla city. The physical indexes and engineering properties tests were used to determine the natural water content, Atterberg limits, particle size distribution of soils, shear strength of soils by Torvane Technical, moisture-density relationships of soils and unconfined compressive strength. Undisturbed samples were extracted from depths more than 150 cm by cylinder cores. The chemical tests included sulfate content, gypsum content, total dissolved salts and pH value test. The results revealed that shear strength of soils is reduced when the plasticity index and natural moisture content increased. The results from the Torvane technical device tests of the soils revealed that the Torvane technical device is very easy, quick and accepted and it is in demand for engineering uses and may be used in laboratory and field.


INTRODUCTION
In the geotechnical research community, there is widespread agreement that the option of the characteristic undrained shear strength is very important and plays an essential role in the calculation of the design and stability analysis of different geotechnical structures placed in or on soft clay layers.Thus, the option of undrained shear strength, both conservative and non-conservative, could have greater economic (and social) consequences in several projects.However, the effect of the stress history, soil structure, strain rates, Atterberg limits, sampling technique, and sample disturbance is great on the undrained shear strength of soft clays.Consequently, the estimation of the representation of the soft clays has been challenging since the beginning of the concept.A simplified approach is therefore DOI: 10.46717/igj.51.1.5Ms-2018-06-27adopted for design purposes.It needs to be emphasized that (Cu) from the soil is the undrained shear strength that is assumed to be rallied along the slip surface 45° inclined from the major principle stress (Abusharar, 2016).
The undrained shear strength cu profiles with depth are ordinarily determined at some selected boreholes where the information is collected.These cu profiles are later interpolated to the soil volume between the boreholes.Thus, the reliability of a cu profile at the boreholes is fateful because the soil volume between the boreholes depends on the representation of the cu profiles at the boreholes (Das, 2006).
The study area is located in Hilla city, Babylon province, in central part of Iraq within the Mesopotamian Zone, and away of about 100 Km south of Baghdad.It is flat with an average elevation of about 28 m above sea level.It is confined between longitudes 00" 24' 44° -00" 26' 44° and latitudes 00" 30' 32° -00" 32' 32° (Fig. 1).The total area of the city is of about 100 Km 2 (Jubouri, 2002)., 1980).The study area is characterized by sediments of Quaternary (Flood Plain sediment) for each of the Euphrates river and its branches (Al-Kadhimi et al., 1996).
This study aims to determine the shear strength of soils at selected sites in Hilla city, using a modern device of fast technology.The relationships between the measured shear strength and some engineering and physical properties of the soil are presented.
These parameters may be used in determining soil suitability and bearing capacity for the construction of structures, buildings and residential buildings.
There are also sediment of (depression fill sediments) and these sediments resulted from floods, they are composed generally from thin layers of sand and silt, clay and silt loam, the sediment aerobic (aeolian sediments) are found in the eastern portions of the province as there are dry Marsh deposits in different parts of the studied area (Parsons, 1957).
Sediments that exist as a consequence of human activity and that are remnants of ancient channels, Antique small hills, represent ancient residential regional , became represent natural phenomena after long years from disappearing , in addition to being an important geomorphological phenomena of a flat alluvial plain (Al-Jubouri, 2002).

FIELD WORK
The reports, research and some studies on the studied area were collected.The previous result tests of selected sites were analyzed after field reconnaissance and the subsurface investigation about of the city is studied.The three selected sites are: Street 80 area, Althala area and Al-Bakarly area.These sites were identified by Global Positioning System (GPS) (Fig. 1).Samples were taken by hand an auger at a depth does not exceed two meters from the surface to obtain undisturbed samples.A cylindrical tube was inserted pay them firmly within a layer to take the undisturbed samples.
The soil samples were described visually in the field, and put in nylon bags, to keep the samples from damage and to keep the natural moisture content.The soil then moved to a laboratory to conduct the required tests, which were depended by Hijjawi (2003) as shown in Table (1).

THE TORVANE SHEAR TESTER
Vane shear test apparatus modified to be called (Torvane shear tester) as shown in  (Das, 2006).

Fig. 2: Torvane shear tester
Torvane shear tester, which was used in this paper, is mounted manually and presence of pulsed spiral (Spring) within its design is linked to a scale mechanic (Gage) calibrated in advance and this device may be used to calculate the undrained shear strength, both disturbed and undisturbed samples in the laboratory or in the field of the work of investigations and explorations to the soil.This device is used to measure shear strength of the undisturbed samples taken from the selected studied sites.

UNDRAINED SHEAR STRENGTH TEST
The Torvane is pushed into the soil and then rotated until the soil fails (Fig. 3).The untrained shear strength can be read at the top of the device from the scale (Gauge) Calibrated dial, and thus the advantage of this device is that it is easy and quick to use and give results for the shear strength in situ and laboratory and with a simple technique (Das, 2006).
This test represents a primary purpose of the search terms were calculated the undrained shear strength (Cu) for three samples of soil by (Torvane) after they have been taken samples is confused by taking Cores by cylinder metal has been processed, from specific locations and brought to the laboratory for purpose of test by device the (Torvane) and calculate the shear strength for each specific samples, where it was the work of measurement on the form in more than one location at the center of pulp and when aspects of the homogeneity of the test in all locations of surface-to-door samples and after test the shear strength was calculated water content directly at three sites per core, of the top and the middle and bottom of the core one.Atterberg Limits, which are the Liquid limit (LL), it represents the nature content which turns soil from the case of plasticity to the liquidity situation by using a Gasagrande apparatus (Lambe, 1951).Three samples were taken within the studied area to identify each sample Liquid limit (LL), plastic limit (PL), and also plasticity index (IP) mathematically calculated by the following relationship.(I.P = L.L -P.L).
Where these limits were carried out according to standard ASTMD 4318-84.
Grain Size Analysis, this examination of raw soil was conducted by using the method used by the American Society of tests and materials (ASTMD 422-84).The test was conducted by washing approximately 200 gm of soil in a sieve No.200, and drying the remains on the sieve No.200 and a sieve analysis a number of sieves as softer at the bottom to get the sand and gravel rate and transit sieve 200 taken from 50 gm of dry soil, and treated with dispersant Material is material Hex-met-phosphate sodium, being his hydrometer analysis to get the proportion of clay and silt.

Engineering tests
Engineering tests were conducted in the National Center for Construction Laboratories (NCCL) in Hilla city, as well as a Laboratory in the Department of Applied Geology, Science college, Babylon University and About fifteen soil samples were taken from these sites at various depths and the performed engineering tests included following: untrained Shear Strength test, it was conducted using the device Torvane (Das, 2006).Three samples from the field were tested with undrained shear, often used to determine the shear strength of the soft clay soil with high humidity by Vane Shear Test (Chandler, 1988).
Moisture-Density Relationships, to determine the maximum dry density and optimum moisture content to three soils, testing was conducted according to standard ASTMD 698-78.
Unconfined Compressive Strength test, to determine the compressive strength of three Soils, the testing was conducted according to standard ASTMD 2166-82.

D = dilution
Gypsum content, which is calculated mathematically by multiplying the proportion of sulfate to the soil × 2.15, as follows: Gypsum = proportion of sulfates × 2.15% ………………….3 PH-value, the concentration values of pH in natural soils of the study areas were identified on the way provided for (Eades and Grim, 1966).

RESULTS AND DISCUSSION
1. Atterberg Limits, Table (2) shows that Index values for soils in the studied sites are close together because the convergences of the percentages of the components are simple in terms of the soil (gravel, sand, silt, clay).(5, 6 and 7) and Table (2

Fig. 1 :
Fig. 1: Satellite image for the locations of the samples in the study area

Figure ( 2
Figure (2).Where the measured shear strength in a manner vane shear test laboratory and on site, and can determine the shear strength in other ways using the principle of the same method to cut the vane shear test including screening device the (Torvane shear tester) in addition to device (Pocket Penetrometer) to the soil(Das, 2006).

Fig. 3 :
Fig. 3: A process to test the shear strength by device Torvane PHYSICAL, INDEX AND ENGINEERING TESTES These tests were carried out on the three soil samples representing the three areas, namely, (Street 80, Althayla and Al-Bakaerly, and these tests were conducted according to specifications of the American Society for Testing and Materials (ASTM) and included the following tests: 100% ……. 1 The total weight of the sample Total soluble salts Test (TSS %) was to find depending on the method mentioned in the Earth manual in ASTM moisten the soil sample weight of 10 gm distilled water weighing 500 gm (i.e., by 1 -50) gm and the use of vibrators and duration intermittent per hour for a period (four days) and filtered on filter paper (1), and calculates the following equation.of salts Salt Content difference between the weight of Albeckr empty and filled with a weight.
) show the percentages of soils and their distribution by size distribution curves and these percentages denote the deposition original of the study area.

3.
Shear Strengths, Table (2)  shows that the values of shear strength for both tests performed are almost convergent values and the difference is due to the testing method used and this proves the significance of the Torvane device.

Fig. 5 :
Fig. 5: Grain size distribution curve of sample for Thayla area