VARIATION IN BEARING CAPACITY OF CONTAMINATED LATERITE SOIL. Dr R N Khare

Transcription

1 VARIATION IN BEARING CAPACITY OF CONTAMINATED LATERITE SOIL Dr R N Khare Professor, Civil Engineering & Principal Shri Shankaracharya Engineering College, Bhilai Prashant Pathak Research Scholar, SaiNath University, Ranchi (Jharkhand) INDIA ABSTRACT Soils of Madhya Pradesh and Chhattisgarh are varied in types, and are suitable for production of different crops. However the availability of soil nutrients varies in different areas, posing a large number of problems. This research paper gives detail information with respect to soil nutrient status, problem soils, its bearing capacity, their ground improvement techniques & its management for better crop production. Keywords: Soil, Bearing capacity, Problematic soils and its Ground improvement techniques. 60

2 Introduction This research paper covers a detailed study on the presence of laterite, their various compounds, nature and levels of trace and toxic contaminants of laterite soil of Jabalpur, MP &Bhilai (Chhattisgarh State) India and abroad, causes of laterite in soil and the effect of laterite in soil has been carried out in a large number of soils. Special emphasis has been placed on the characterisations (Strength) of soil for Jabalpur &Bhilai block of Durg district. High alkaline and non alkaline concentrations have been observed at numerous sites around the Chhattisgarh and Jabalpur (MP) region. Tests were conducted to determine the property of soil with variation of water content for soils under different stage of water flow. The soils had varying amounts of plasticity s ranging from low to high plasticity. The unsaturated soil behavior was investigated for different conditions, covering a range of compactive efforts and water contents. Therefore, an experimental study was carried out to determine the geotechnical properties of the contaminated and non-contaminated soil through various tests for Characterization of laterite soil. The bearing capacity is also determined for contaminated and non-contaminated soil for the above areas where the laterite soil is weak because of alkaline contamination. Some treatment through adding sand (varying % of sand),stabilization measures like addition of coconut oil, flyash and solid wastes (silica fume and aluminum sludge) in alkaline contaminants soils are proposed and tested successfully for improving the quality of soil. A comparative computation of bearing capacity considering the value of internal friction and all other facts, for uncontaminated and contaminated soil and keeping all other parameters in account, it shows 1.5 to 2 times reduction in bearing capacity after contamination but after addition of iron and Mn /Zn bearing capacity is being enhanced which is also being further enhanced by addition of sand from 2-6% by wt of soil (report: Yadavetl). The Physico-Chemical Properties Of Alkaline: The most common amendment to increase soil ph is lime (CaCO 3 or MgCO 3 ), usually in the form of finely ground agricultural lime. The amount of lime needed to change ph is determined by the mesh size of the lime (how finely it is ground) and the buffering capacity of the soil. A high mesh size (60 100) indicates a finely ground lime, that will react quickly with soil acidity. Buffering capacity of soils is a function of a soils cation exchange capacity, 61

3 which is in turn determined by the clay content of the soil, the type of clay and the amount of organic matter present. Soils with high clay content, particularly shrink swell clay, will have a higher buffering capacity than soils with little clay. Soils with high organic matter will also have a higher buffering capacity than those with low organic matter. Soils with high buffering capacity require a greater amount of lime to be added than a soil with a lower buffering capacity for the same incremental change in ph. Other amendments that can be used to increase the ph of soil include wood ash, industrial CaO (burnt lime), and oyster shells. White firewood ash includes metal salts which are important for processes requiring ions such as Na + (sodium), K + (potassium), Ca 2+ (calcium), which may or may not be good for the select flora, but decreases the acidic quality of soil. These products increase the ph of soils through the reaction of CO 2 3 with H + to produce CO 2 and H 2 O.Calcium silicate neutralizes active acidity in the soil by removing free hydrogen ions, thereby increasing ph. As its silicate anion captures H + ions (raising the ph), it forms monosilicic acid (H 4 SiO 4 ), a neutral solute. Experimental Observations: COMPARISON OF GEOTECHNICAL PROPERTIES IN ORIGINAL, ALKALINE CONTAMINATED LATERITE SOIL OF DIFFERENT SITE 62

4 Table Sr. Engineering Original Uncontaminated Contaminated soil Contaminated soil After adding 10% No. Properties of soil Soil soil at Lab in site sand in the laterite (2) (3) (Near the site) (4% NaoH by (6% NaOH by soil (4) Wt) Wt) (5) (6) 1.Grain size analysis % Gravel - % Sand % Silt % Clay Atterberg s Limit: %LL %PL %SL %PI Compaction characteristics OMC % MDD (KN/m 3 ) Swelling characteristics: 63

5 Swell (KN/m 2 ) Pressure Diff. Free Swell (%) I.S.I. Classification CH CH CH CH CH Percentage of alkaline removal by Electrokinetic Model Apparatus Allowable bearing pressure in (KN/m 2 ) At a) 1m, when S p = 2.5cm b) 3m, when S p = 3.05cm c) 5 m, when S p = 4.5cm

6 Graphs 1 and 2 shows about the characterization of soil- Result and Discussions: The shear strength of soil is reduces due to the improper Alkanity and Chloride content present in the surface and ground water (alkanity and chloride content was 140 mg/l and 249 mg/l in the ground water/surface water which is less than the permissible value 200mg/l and 250 mg/l respectively and it is responsible for reducing the bearing capacity of soil). to Thixotropy character of soil (strength gainstrength loss process). From plasticity chart and by the observation result it is seen that the classification of soil is SW (Well graded sand as more than half the portion of the soil passes through 4.75 mm sieve, the soil is essentially sandy)) after addition of Ground water/surface water as PI was 5.68 % and 0.7% in the soil respectively. After due course of time soil becomes more plastic in 7days if it is contaminated with surface water/ground water and it is mentioned below is observed: Cu, Cc, LL, PL, OMC, MDD,G and Water content is increases initially if the soil is contaminated with GW/SW and then after 7 days it reduces and again increases after 10 days due Conclusions: It is observed that due to addition of ground water in soil finer particles are absorbing the moisture and it becomes coarser particles. an initially bulk density increases up to 7 days afterwards it decreases if we add more water. It is observed that due to addition of surface water in soil dry density reduces because of 65

7 contamination present in the surface water. It is also concluded that the changes in the particle sizes are irregular and the particles are disintegrated in to the finer particles. The loss of strength due to remolding is partly due to a) permanent destruction of the structure due to in-situ layers and b) reorientation of the molecules in the adsorbed layers. The gain is strength is due to rehabilitation of the molecular structure of the soil, and is due to its thixotropic property. References: 1. Rao A.S. etal (2004), Compression Test on Granular Pile Anchors Embeded in Expansive Soil, IGC,Varangal. 2. Soil mechanics and Foundations by Dr B C Punmia (16 th Edition) 2005,p30,78, Bowles, J.E. Foundation analysis and design Mcgraw hill. Newyork Unified design of piled foundations with emphasis on settlement analysis by { Bengt H. Fellenius, Dr. Tech., P.Eng Alexander Street SE, Calgary, Alberta, T2G 4J3} 66