Geotechnical and Hydrological Characterization of Subsurface for Metallic Minerals Mining Operations in Punjab, Pakistan

The study area is covered by alluvium having average thickness of about 200 m that is underlain by the Precambrian basement rock units including iron ore to be mined in future. In this regards, necessary campaign of subsurface investigations including both geotechnical and hydrogeological has been carried. In geotechnical investigations, disturbed and undisturbed samples were collected from five (5) boreholes and hydrological investigations by using water pump out test were conducted to determine the characteristics of aquifer. Rock samples were also collected from already drilled boreholes for iron ore estimation from a depth of more than 200 m. The laboratory testing has classified alluvium as silty sand/sandy silt (SP-SM/SM) and clayey silt/non-plastic silt (CL-ML/ML) as per soil classification criteria having angel of friction of 31.4 38.5 degree with bulk density of 1.461 1.853 g/cc. The initial void ratio (eo) varies from 0.412 to 0.952 with no swell potential in consolidation tests. The chemical analyses of the soil have indicated values of 0.003% 0.006%, 0.0012% 0.0057%, 0.013% 0.030% sulphate, chloride and organic matter contents respectively with pH-value of 6.92 7.56. The strength of the underlying rock was found to be medium strong to very strong corresponding to values of 25 140 MPa in uniaxial compression and indirect tensile strength of 15.66 MPa. Hydrological study reveals that aquifer is unconfined and generally isotropic in nature. The average transmissivity, hydraulic conductivity and storage coefficient are 6038 m/day, 4.0 × 10 m/day and 0.016, respectively that presented aquifer is quite permeable. The cone of influence covered area of 65 m from main production well. For the open pit mining operation, stability analysis is performed by assuming a 4V:1H slope in the bedrock while 1V:1H in the overlying sediments cover using Limit-Equilibrium (LE) analysis in Slide computer program. However, overburden slope was concluded to be unstable with the analyzed slope angle. The How to cite this paper: Akram, M.S., Mirza, K., Ali, U. and Zeeshan, M. (2019) Geotechnical and Hydrological Characterization of Subsurface for Metallic Minerals Mining Operations in Punjab, Pakistan. Open Journal of Geology, 9, 752-767. https://doi.org/10.4236/ojg.2019.911088 Received: September 4, 2019 Accepted: September 27, 2019 Published: September 30, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
The location of the study area is situated in Punjab ( Figure 1) approximately 158 km North-West from Lahore and located on the left riverbank of Chenab near Chiniot town that is bounded with rock outcrops of Kirana and Sargodha. This study emphasized on geotechnical and hydrological characterization of subsurface in view of mining activities for metallic mineral in future. Paige-Green [1] studied distribution parameters of soil particle size. Erguler [2] investigated grain size distribution of soil by using quantitative methods. Giasi et al. [3] studied several equations correlating soil's properties of compressibility to its liquid limit and plasticity index properties. Messad and Moussai [4] tested samples that were prepared by using distilled water with different salt concentrations and results displayed the decrease in pore fluid salinity by using procedure of conventional water content and increase by using method of fluid content. Ogunsanwo [5] investigated characteristics of shear strength of laterite soils of Nigeria influenced by preparation of samples and testing modes. Marsland et al. [6] conducted the site investigation for foundation and earthworks of soil.
This study accentuated the geotechnical investigation, the characteristics of subsurface materials, and the details of field and laboratory testing. The hydrological study is also planned to determine the characteristics of groundwater aquifers and preliminary slope stability analysis is also analyzed by using Limit-Equilibrium (LE) analysis.

Methodology of the Study
The detailed methodology to carry out this study is presented in Figure 2.

Tectonics
Punjab province in eastern Pakistan lies on the northwestern margin of the Indian continental tectonic plate, the slow northward migration of which has resulted

Geology
The field investigation developed the understanding of the study area that is covered by both the loose overburden materials and the rock formations. In Study area, the recent alluvium deposits of unconsolidated and uniform in nature are being deposited by the Chenab River. Sediment deposit is consisting of silt, clay, loam, sandy clay, sand and silty clay. There are two stratigraphic units Hachi Formation, Asianwala Formation are exposed around the study area.

Asianwala Formation
Asianwala Formation is well exposed on the western side of Chenab River. The formation consists of quartzites, slates, phyllites and tuffs. Quartz veins, dolerite dykes and sills are intruded at places [8] [9].

Hachi Group
The lithology of Hachi group comprised of phyllites, quartzites, slates and tuffs.
The light grey color of volcanic breccias is consisting of fragments of rock and

Field and Laboratory Studies
Geotechnical investigations are carried out to define geotechnical conditions of both rock and soil at site for development mining activities in the future. Therefore, five (5) boreholes were drilled up to the depth of 70 m at angle of 90˚ to determine the subsurface properties of strata. The borehole locations are given in Figure 4.

Subsurface Exploration
Straight rotary method was used to drill five (5) (Vallejo 2007). The loose material from boreholes was removed properly before each SPT and by using split spoon sampler disturbed soil samples were gathered.
Total 77 SPTs were carried out at various depths and the data obtained by these tests was used to determine the compactness of sediment cover.

Disturbed and Undisturbed Samples
Total 11 undisturbed samples were conducted from boreholes by using pitcher

Water Pump out Test
The Pump out test is used to determine the characteristics of groundwater aquifers by installing pumping well and observatory wells [17]. Mironenko [19] studied the aquifer properties by pump out test. In this study test was conducted to determining the aquifer properties for mining purpose. The production tubewell upto 76 m depth were installed including three (3)  ( ) Open Journal of Geology s = the drawdown in piezometer at a distance "r" from well. Q = well discharge in m 3 /day. T = the transmissivity of the aquifer in m 2 /day. w(u) = Well function of u and represents an exponential integral. 2 4 U r S Tt = r = distance in meter from the center of the pumped well. S = storativity (dimensionless). t = time since pumping started in days.
Following hydraulic parameters were also measure as discussed below.

Transmissivity (T)
Transmissivity can define the capacity of an aquifer to transmit water and it is a product of the thickness of aquifer (D) and average hydraulic conductivity.

4 T Q s = π∆
Delta can be deduced from time drawdown log.

Laboratory Studies
The number of laboratory tests was performed on collected samples from the boreholes. These tests were performed according to the standard of ASTM and BS [17] [18] [21]. The detailed list of followed standards according to the specific test of soil is given in Table 1.
Similarly, several rock tests were performed by following these standards as mentioned below: • Index Properties Tests (Moisture Content, Porosity and Unit Weight) • Unconfined Compressive Strength Test

Pump out Test
The production well and piezometers were installed to determine the ground- The hydrological study reveals that the water table depth varies from 10 -11 m depth. The electrical conductivity of ground water is <1500 μs/cm that shows good quality of water. The thickness of fresh groundwater is extended to an average The cone of influence covered area of 65 m from the main production well.

Standard Penetration Test (SPT)
The SPT blow counts (N Values) were obtained by all exploratory boreholes.
The uncorrected (N) and corrected (N 70 ) were plotted against depth and presented in Figure 6. The distribution of blow counts with depths was seemed regular. Beyond 30 m depth, the in situ relative density of underneath material feels very dense due to weight of upper covered material. The soil compaction varies between loose to medium dense.

Hoek-Brown Parameters
Hoek-Brown strength criterion is a prevailing empirical tool available in the rock engineering industry for the assessment of rock mass parameters. For this mining project, the rock mass parameters will be mainly required for the underground works. The Hoek-Brown criterion involves the use of uniaxial and triaxial compressive strength testing usually with a set of five samples tested at increasing confining pressure. To date, no triaxial testing has been carried out for which the Hoek-Brown parameters are assumed currently and adopted from the literature review. The Hoek-Brown characterization was performed using the Rocscience software Roclab (Table 2).

Proposed Design Criteria
The mining project would also include several types of structures and geotechnical study is required for the stability of structures foundation as well as excavation • The factor of safety 3 is recommended to secure the foundation by shear failure.
• The angular distortion between two adjacent foundations should not exceed 1/500 in order to avoid differential settlement. • The foundation must stay safe under tensile loading, lateral moment, eccentricity or inclined loading, and vibrational loadings.
Following soil parameters (Table 3) will support engineers to calculate the allowable bearing capacity of various structures and these parameters are based on field and laboratory studies.

Slope Stability Analyses
The accumulation of strain due to excessive deformations for mining leads to the failure of large slopes. Therefore, studying the deformation behavior of geomaterials forms an essential component of designing side slopes of open pit mines.     shown in Figure 10 which shows quite rational patterns of deformation. The maximum deformation is likely to be in order of as high as 700 mm for individual slope riser whereas in the range of 300 to 400 mm for the overall slope. These numbers should become more representative with expanding the geotechnical database for the project and carrying out numerous such analyses with excavation stages since the modulus to elasticity in both soils and rocks is not a constant rather depend on the changing stress and strain.
Following analyses are made at this stage for preliminary understandings when very limited information is available to study the slope stability conditions. Therefore, it is highly recommended that detailed slope stability analyses will be carried out at the stage of detailed design for mining.

Conclusions and Recommendations
This study was conducted to determine the initial geotechnical and hydrological characterization of the study area with the context of infrastructures for mining activities of iron ore in future. Therefore, following points are concluded: • Several samples of soil and rocks were collected to understand the geotechnical properties of the study area. Following laboratory tests of soil and rock  that presented aquifer is quite permeable. The cone of influence covered an area of 65 m from the main production well. • Slope stability analyses were also carried out by using Slide software. The stability analysis is performed assuming a 4V:1H slope in the bedrock while 1V:1H in the overlying sediments cover. 0.79 Factor of safety were calculated according to the assumed water table and other conditions at this very initial stage. The software Phase 2 was used for deformation analysis for mine slopes by finite element method. The maximum deformation is likely to be in order of as high as 700 mm for individual slope riser whereas in the range of 300 to 400 mm for the overall slope.
This study is included an initial understanding of geotechnical and hydrological condition of study area and not recommended for detail design of mining.
At this stage the preliminary information was collected for this study and it is recommended to collect the detailed information to enhance the level of confidence for geotechnical and hydrological design related to mining activities. The depth of geotechnical parameters must be extended to the bedrock in order to collect, examine and test the rock samples as well as soil samples at several depths for more improvement of rock mass characterization information.