Engineering and Technology Journal

This paper investigates the impact of the fly Ash addition on the Geotechnical properties of soft soil as well as chooses the optimum percentage added of fly ash. To understand the behavior of fly ash mixed with soil, a number of laboratory experiments testing conducted on clayey soil-fly ash mixture in several percentages (5,10,15,20,25, and 30%) as Atterberg test, Specific gravity test, compaction test, California Bearing Ratio (C.B.R) Test, Unconfined Compressive Strength (UCS) Test, Consolidation Test. Test results indicate rising in plastic limit and liquid limit as fly ash adding. Specific gravity decreased essentially by adding fly ash. Whereas there was falling on the Dry unit weight value with the contract to the decreasing in the water content. The CBR and UCS values were increased with increasing fly ash content. 20% was the optimum fly Ash content. This study also benefits the effective use of fly ash and thus a cost-effective method for improving the soil properties.

This research aims to study the behavior of the sand columns stabilized with silica fume (as an additive with different percentages) and driven in soft soil bed with undrained shear strength (cu) between 16 – 21 kPa. Holesin the shape of columns with diameter 50 mm and length 300 mm have been drilled in a soil bed and backfilled with sand mixed with several proportions of silica fume with 7-days curing. A rigid circular footing with diameter 64.6 mm was located on each column and loaded axially till failure. The results analysis of the model tests indicated an encouraging improvement in load carrying capacity of the columns and considerable reduction in the settlement compared to the conventional stone columns. The bearing improvement ratio and settlement reduction ratio exhibited by the sand columns are 1.18 and 0.71, respectively. The best possible addition of silica fume content in sand–silica fume columns is 7% giving bearing improvement ratio and settlement reduction ratio of 1.56 and 0.5 respectively.

Stone or sand columns are most widely used to improve the engineering properties of soft saturated soils. In principles, sand columns technique is very close to the well-known stone columns technique and the only difference is the backfill materials.
The present work focuses on implementing sand columns in soft soil of different diameters, different relative densities considering both floating and end bearing types.
The model tests were performed inside a steel container (600mm x 600mm and 500mm in height). Sand columns of diameters ranging between 22mm to 50mm were constructed in beds of soil of undrained shear strength ranging between (15-20) kPa. Each individual sand column was loaded vertically through a rigid circular footing of diameters between 28.6mm to 64.7mm provided an area replacement ratio (as) of (0.6),the ratio of column depth to the column diameter (L/D) was (6).
The model test results revealed good improvements of the load carrying capacity of the columns ranging between (1.3 to 1.9) and significant reduction in the settlement over the untreated soil ranging between (0.18 to 0.47). End bearing columns exhibited better results than floating columns and the diameter of column has no effect on bearing capacity as the (as) and (L/D) are constants

The present work investigates the settlement behaviour of weak soils which cover the middle and southern part of Iraq. Physical and chemical properties were studied for weak soil brought up from Baladroz city, Dyalah Governorate. To decrease the excessive settlement of soft soil under study, reed materials which are widespread at Iraq marshes and geogrid materials were selected as reinforcement materials. For this purpose, steel container with dimensions (500 ×250 ×20 mm)
and square footing (80 × 80 mm) were used.To prepare the soil with same
properties of soft soils, the quantity of water was calculated using the liquidity index formula with LI equal to (0.42) corresponding to undrained shear strength of (10 kPa). This value of liquidity index was chosen according to the previous studies which showed that the liquidity index of such soil is ranging between (0.2 – 0.5).
The results of soil model under the applied stress (5, 10, 15, 20, and 25 kPa) marked that the maximum settlement reduction (S/B) is get when the reed mat or geogrid mat is used directly under the footing and this value decreases with increase of the distance between the surface layer and position of the reinforcement. Also, the settlement improvement (St/Sunt) can be clearly seemed for all cases of improvement compared with settlement of untreated soil It is worth noting, that to achieve the durability of the reed in the soil, asphalt coating must be used to prevent the reed decay.