In this research, change in undrained shear strength 5u due to swelling under co and isotropic stress conditions is investigated for reformed Dhaka clay, collected from BUET campus. The uridrained shear strength of naturally occurring Dhaka clay is predicted using the log linear relationship between 5,/6. Relationship between the coefficient k and overconsolidation ratio and ~ tRe effective angle of internal friction Relationship between undrained shear strength and water content for.
It is therefore useful to represent the undrained shear strength relationships in a simple way using a few parametric constants. The present research was conducted to investigate the relationship between equilibrium water content and consolidation pressure and to determine the relationship between undrained shear strength and relevant soil parameters for normally consolidated and overconsolidated condition of Daka clay. This review is concerned primarily with the undrained shear strength characteristics of saturated clay under normally consolidated and prestressed conditions.
Skempton (1942), Skemptbn and Henkel (1957) noted that the undrained shear strength can be related to the modulus of elasticity. Undrained mOdulus_also depends on the amount of limiting modulus of elasticity of the soil, it depends not only on the undrained shear strength, but also on the plasticity and stress index. 110 is called the critical state pore pressure parameter and is equal to ratio of undrained shear strength to overburden for normal_.
The relationship between water content and shear strength in compression, tests on normally consolidated and overconsolidated samples of saturated Weald clay by Henkel (1959) is shown in Fig.
SID (3
INTRODUCTION
From the literature review it appears that the Engineering Properties of a soil depend on the composite .effect of severa). Similar undrained elastic ~Qdulus and coefficient of horizontal earth pressure at rest can also be expressed from certain soil parameters. The aim of the present research was to investigate the selective edge geotechnical properties of Dhaka clay and to establish the relationship between undrained sheBr strength, undrained elastic modulus and coefficient of lateral earth pressure'~with other soil parameters.
OBJECTIVE
The purpose of the present research was to investigate selected edge technical properties of Dhaka clay and to determine the relationship between undrained sheBr strength, undrained modulus of elasticity and lateral earth pressure coefficient with other soil parameters. equal to the angle of effective friction; overconsolidation ratio, critical state pore pressure parameter and w3ter content at normal value. Soil collected from the Bangladesh University of Engineering and Technology campus from a depth of five meters above the ground was used. The procedure recommended by the American Society for Testing Materials (A5TI~) was used to determine the soil index properties.
The side of the cell body was covered with a thin layer of silicone grease to minimize lateral friction. Two filter papers were placed on the disk located at the bottom of the cell. To check the uniformity, density and water content of the sample, five different species were determined.
After the slurry was poured into the oedometer, a porous stone and a spacer block were placed on top of the slurry. The slurry was then consolidated by gradually increasing the vertical pressure to. the final value.'. The load was applied until consolidation was complete, which was indicated by the constant reading of the strain gauge.
After removing the soil specimen from the brass tube, it was trimmed to a height of 2.8 inches. The top drive assembly 'A' was positioned so that the top of the receiver contacts the center of the cover 'g'. The distance between the driven impeller was the change in length of the specimen due to consolidation.
After the end of the test, the apparatus was dismantled and the specimen was put into the oven for After the final reading, the apparatus was disassembled and the weight of the 'soil' specimen was taken. It is observed that for the same vertical consolidation pressure, the undrained shear strength for the isotropically consolidated samples is higher than that of the k-consolidated samples.
Dhaka, the clay from this figure is found to be 25 • The value of Ao calculated from the equation i-c ./c. 5.6.
Undrained shear strength versus Qver- consolidation ratio for isotrQpieally
The slope of the line thus determined from the graph will henceforth be referred to as. From the experimentally determined values shown in Table 5.5 it can be seen that 110 is for isotropically consolidated samples. The value of ~o for this natural Dhaka clay is 0.958, while the experimentally determined values for reformed Dhaka clay are 0.85 in ko condition.
This discrepancy between natural soils and reshaped soil is probably due to some uncertainties in the estimation of the overconsolidation ratio of the natural deposit. In this model, the overconsolidation ratio is calculated based on the water content versus iog of the consolidation;:pressure v curve shown. in figure 5.13. For example, a point corresponding to .. vertical in-situ stress and soil water content is initially placed at point A.
A line parallel to swelling curve and . through that point corresponding to k state intersects the o . normally loaded state's consolidation curve at point 8. The . .,.,I. VERTICAL CONSOLIDATION PRESSURE lo-v) IN PSI. Similarly, the line corresponding to isotropic state ~from the normal state consolidation comes at another point t, The consolidation . pr'S[11o;ted fromisotrop5,cally conso,U.r.Jated model and k conso . . , 0 . cover decorated mod,eJ. and the strength or ne.tLJra,lsoil' after LJndist'LJr- b'ed s~mplingo nverconsolidation'n. r"tio was determined .. from the water content and the vertical pressure from the general curves for O, a soil shown in Figo 5-14. There is some scatter in the estimated strength of the soil to actual strength which is measured At the same time, further study is also required to obtain more controlled field data with actual field strength tests to verify the applicability of 'the proposed mOBel for Dhaka clay.
5~15' represents water content versus undrained shear strength, for isotropically consolidated and kD consolidated Dhaka clay under normal stress condition. It can be seen from this figure that the curve for the isotropically consolidated Dhaka clay is very close to the normalized curve they plotted. Vertical height of overconsolidation Lateral coefficient of effective specimen at lidation stress on lateral consolidation of consolidation Earth pressure ratio .. dation psi at rest . inch pressure k . dogs 0.
It can be seen from Figure 5.17:b) that the coefficient of lateral earth pressure at rest (k) essentially remains. 5.17(b) Dependence of the opening pressure on the coefficient of co~. k determined when determined when determined when determined e~p erimentall y from empirical from curve from curve. This means that the experimentally determined value of a for Dhaka clay is greater than that recommended by Alpan (1967) and Flavigny (1980).
CONCLUSION AND RECOMMENDATION FOR FUTURE RESEARCH
Undrained test path for firgin compressed
Critical state pore pressure parameters
Mohr-Rankine criterion
It has been seen that the cDhesive sDil, or ratiD vDid Dr dr structure Df soil, Dr bDth ch~nge during the cutting prDcessit and the ratiD.,vDid .vary with the effective stress. Because the rebDund characteristics Df sDils such when subjected tD applied Dr remDv~l Df effective stress, important investigations Dut been performed with Dbject Df determining the variatiDns Df shear strength DfsDil at a cDnstant vDid ratiD. B-1 shows the bond failure rate and the effective stress of a shear, strength, and shear stress.
The effective stress axis is C?mmDn tD bDth figure and refers .this example tD nDrmal stress Dn plaRes failure. RatiD vDid used in this diagram in the vDid ratio at failure in the shear test under nDrmaleffecti0e shDwn stress at the top. In the effective normal stresses represented by the abscissas of the diagram, the.
From a number of test~ it was found that ~ is independent of void ratio log Ceta void ratio becomes Using the equation can be written as.
APPENDIX C
Typical stress condition at the end of ~onsolidation
