In order to determine the soil and rock properties related with the slope stability along the East Coast Expressway (km??), field and laboratory work have been conducted in carrying out this research. The field work are conducted in order to obtain the sample and slope orientation (Dip and Strike). The laboratory work will be conducted to check and determine the properties and also the strength of the soil and rock.
The aim of the field and laboratory work is to gather parameter for soil and rock for slope stability. The methodology of the research implemented in order to achieve objective is shown in Figure 3.1. The research is conducted along the slope at Km?? East Coast Expressway.
Figure 3.1: The flow chart of methodology
3.1 Discontinuity Survey
Discontinuity in geological engineering can be defined as a plane or surface that marks a change in physical characteristic in soil or rock mass. The discontinuity survey involved data collection for dip and dip direction along the study slope. The data are used in the discontinuity analysis in order to produce engineering geological map. Stratum Compass or Smartphone was used to measure and take data of dip and dip direction. The method are carried out by walk along the slope and record the data of dip and strike. Dip is the maximum inclination of a structural discontinuity plane to the horizontal while dip direction is the direction of the horizontal trace of the line of dip measured clockwise from north.
The data obtain was then analyzed with the software such as DIPS software to determine the mode of failure of the slope along the stretch. The discontinuity survey also involves with the observation and checking of discontinuity condition such as surface roughness; groundwater at the discontinuity either if flow, dripping etc. The will be used as a parameter for rock mass rating.
Figure 3.2: Definition of geometrical terms (Hoek and Brown, 1980)
Soil sample are taken along the stretch for laboratory test and analysis by using auger. Samples will be collected at different level at different marking point along the study slope. The sample will directly put into the plastic bag once it taken in order to preserved it original moisture contents and condition.
Dynamic Cone Penetrometer
Dynamic Cone Penetrometer (DCP) is an equipment used for the in-situ measurement of the structural properties of existing road pavement constructed of unbound materials. It provides a measure of a materials in-situ material to penetration. The DCP is very simple in design, quick to use, portable and suitable for use in location where access may be difficult.
Test result can be correlated to California Bearing Ratios, in-situ density, resilient modulus and bearing capacity. The DCP applied the same concepts with the JKR Probe or Mackintosh Probe but just different in term and application of method.
3.3 Laboratory Testing
3.3.1 Particle Size Distribution
A sieve analysis is a test are used assess the particle size distribution of soil or granular material. It involves determining the percentage by mass f particle within different size range. Particle size distribution is an index or expression inducting the sizes of the particles resent in that what proportions in the sample particle group to be measured and the particle size can be classified depending on their percentage. The procedure started by weighting each sieve and dry sample. The sample then are placed into the sieve and start shaken around 10 minutes. The mass of retain in every sieve is recorded as percentage amount of the sample. .
3.3.2 Moisture Content
The soil samples collected from the site were immediately stored in the plastic bags after taken in order to prevent moisture loss to the surrounding. The most commonly and standard test used to determine the moisture content is by dry the soil sample in the oven. The different between weight or mass before and after oven dry are used to determine the moisture content in the soil sample.
3.3.3 Atterberg Limit Test
The Atterberg limit test is used to describe the shrinkage limit, plastic limit and liquid limit of fine-grained soil. This test indicates the stiffness of cohesive soil and carried out on the portion of the soil finer than 425?m. In determining the liquid limit, cone penetrometer test was used. This is the preferred method for liquid limit determination. In this test, the soil sample is placed in a 55m diameter, 40mm deep metal cup and will be penetrate by a stainless steel cone weighing 80g and having a 30° angle in 5 second when allowed to drop from position point contact with the soil surface. The test if performed multiple times (4 or more) at various moisture content to determine the fall cone penetration. Then, the relationship between moisture content and cone penetration are plotted to determine the liquid limit where the moisture content correspond to cone penetration of 20mm is taken as soil liquid limit.
Plastic limit test are used to determine the moisture content at which soil begins to behavior as a plastic material and where the thread breaks apart at a diameter of 3mm. The test is carried out by rolling the soil sample into threads of 3mm diameter on a flat, non-porous surface.
3.3.4 Soil and Rock Strength Test
Shear Box Test
The shear box test is used to determine the shearing strength of the soil sample on a predetermined shear plane. The test is performed by placed the sample in a shear box which has two stacked rings to hold the sample. A confining stress is applied vertically to the sample and the upper ring is pulled laterally until the sample fails, or through a specified strain. The value load applied and the strain induced is recorded to determine a stress-strain curve for each confining stress. The shear strength parameters are then acquired from the best line fitting the plotted points.
In many engineering design such as retaining wall, the value obtain from these test which s angle of internal friction and cohesion is very important. For this project, both soil and rock sample will undergo shear box test but different in equipment and loading.
Point Load Test
Point load is used to determine the rock strength indexes. It is widely used in classification for rock, both in the field and in the laboratory. The test is conducted by performing a rock sample to an increasingly concentrated loads until failure occurs by splitting the specimen. The failure load are used to calculate the point load strength. The result from this test will be used as a parameter for rock mass rating.
3.3.5 Mineral and Crystalline Analysis
X-ray Diffraction (XRD) Test
XRD is the primary, non-destructive analytical method for identifying and quantifying the mineralogy of crystalline compound, chemical composition and physical properties in rock and soil. XRD finds the geometry or shape of molecule by hitting the sample with X-rays beam. It start with the projection of monochromatic X-rays onto the sample at an angle diffraction occurs when the distance traveled by rays reflected from successive planes differs by an integer of wavelength. The result will produced a characteristic pattern from the plotted angular positions and intensities of the resultant diffracted peaks. In this research, both sample which is rock and soil are analyzed with XRD in determination of mineral content.
This method are used to determined and identify the mineral content inside rock. In order to conduct this test, the thin section is prepared. The petrographic microscope transmits polarized light through the thin section, in which the thin section are placed between two polarizing filter oriented orthogonally to each other. The mineral content in the thin section will alter the colors and intensity of light as seen by the viewer. Different minerals will produce different color due to different optical properties. This test can be used to identify most of the constituent minerals in a rock and to some extent, mineral composition.
3.5 Software Analysis
SLOPE/W is one of the software uses to analyze and computing the factor of safety of soil and rock slope. SLOPE/W can effectively analyze both simple and complex problem for a variety of slip surface shape, pore water pressure conditions, soil properties, analysis method and loading condition. SLOPE/W use limit equilibrium theory in modeling the heterogeneous soil types, complex stratigraphic and slip surface geometry and variable pore-water pressure condition using a large selection of soil model.
The software using various method of slice for limit equilibrium analysis such as Bishop’s Simplified, Ordinary method of slice, Spencer and Janbu’s simplified. The analysis provide a factor of safety of the slope either it is stable or unstable. The result of particular method can be vary due to different in assumptions and satisfied equilibrium conditions. The parameter of the slope such as unit weight, angle of internal friction and cohesion are obtained from the laboratory testing and previous recorded data during the construction of LPT 1.
DIPS is designed for the interactive analysis of orientation based on the geological data such dip and dip direction. Dip and dip direction data was then analyzed with DIPS software for discontinuity analysis result in the type mode of slope failure. The program is fit for some application and is intended for the occasional user.
DIPS allows the user to analyze and visualize the information or data following the same procedures utilize in manual stereonets. Also, it has numerous computational highlights, for example, mean orientation and confidence calculation. It is designed for the analysis of features related to the analysis of rock structures.