Soil samples can be of two types:
(i) Disturbed samples.
(ii) Undisturbed samples.
A disturbed sample is that in which the natural structure of soil gets partly or fully modified and destroyed although with suitable precautions the natural water content may be preserved. Such a soil sample should, however, be representative of the natural soil by maintainlng the original proportion of the various particles intact. An undisturbed sampleis that in which the natural structure and properties remain preserved.
The sample disturbance depends upon the design of the samplers and the method of sampling. To take undisturbed samples from bore holes properly designed sampling tools are required. The sampling tube when forced into the ground should cause as little remoulding and disturbance as possible. The design features of the sampler, that govern the degree of disturbance are (i) cutting edge (ii)inside wall friction and (iii) non-return valve.
Fig. 1 shows a typical cutting edge of a sampler, with the lower end of the sampler, with the lower end of the sampler tube.
The area ratio should be as low as possibie. It should not be greater than 25 percent; for soft sensitive soil, it should preferably not exceed to porcent. The inside clearance should lie between 1 to 3 percent and the outside clearance should not be much greater than the inside clearance. The walls of the sampler should be smooth and should be kept properly oiled so that wall friction is minimum. Lower value of inside clearance allows the elastic expansion of soil and reduces the frictional drag. The non-retum valve, invariably provided in samplers, should permit easy and quick escape of water and air when driving the sampler.
Types of Samplers
The samplers are classified as thick wall or thin wall samplers depending upon the area ratio. Thick wall samplers are those having the area ratio greater than 10 percent. Depending upon the mode of operation, samplers may be classified in the following three common types :(i) open drive sampler (including split spoon samplers), (ii) stationary piston sampler and(iii) rotary sampler.
The open drive sampler is a tube open at its lower end. The sampler head is provided with vents (valve) to permit water and air to escape during driving. The check valve helps to retain sample when the sampler is lifted up. The tube may be seamless or it may be split in two parts; in the latter case it is known as split spoon sampler.
The stationary piston sampler consists of a Sample cylinder and the piston system. During lowering of the sampler through the hole, the lower end of the sampler is kept closed with the piston. When the desired sampling elevation is reached, ihe piston rod is clamped, thereby keeping the piston stationary, and the sampler tube is advanced down into the soil. The sampler is then Iifted up, with piston rod clamped in position. The sampler is more suitable for sampling soft soils saturated sands.
Rotatory samplers are the core barrel type having an outer tube provided with cutting teeth and a removable thin wall liner inside. It is used for firm to hard cohesive soils and cemented soils.
Average Daily Traffic (ADT)
The volume during a given time period (in the whole days greater than one day but less than one year) divided by the number of days in that time period and expressed in terms of veh/day.
Average Annual Daily Traffic (AADT)
It is the total yearly volume divided by the number of days in a year.
Design Hourly Volume (DHV)
It is the economic hourly flow of future year, which is used for designing geometric features of roadway.
The vehicle whose weight, dimensions and operating characteristics are used to established the geometric standards of the highway
The design speed is defined as the “maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of highway govern
The capacity of a given section of roadway may defined as the maximum hourly rate at which vehicle can reasonably travel a point or uniform section of roadway during a given period under prevailing roadway, traffic and control conditions
Level of Service (LOS)
Level of service is a qualitative measure that describes operational condition within a traffic stream and their perception by road users.
Lane width usually vary from
A median is the section of a divided highway that separates the lanes in opposing directions
Right of Way
The right of way is the total land area acquired for the construction of the highway
Physical devices which is used to control and guide motorist, prevent vehicles from leaving the roadway and crossing into wrong side, facilitated drainage.
Median and roadside barrier, guardrails/ Guard post, Curbs and Gutters, Island/Channel, Sign, signal, light post
The maximum hourly rate of an approach at a signalized junction/ the maximum rate of discharge for a particular approach
Flow that is generated because of new or improved roadway facility
When demand is at or near or exceeds the roadway capacity and the average rate of flow remains almost constant with time.
When land changing opportunity decreases with increasing traffic volume and drivers are forced to follow slow leaders.
Passenger Car Equivalent (PCE)
It is the method of expressing various types of vehicles having different characteristics in a common equivalent unit. One car is considered as one unit.
In respect to its road occupancy and operational requirements each type of vehicle is equivalent to a number of passenger cars and this is called the Passenger Car Equivalent.
Amber period/Clearance time (a)
To allow vehicles to clear the junction (usually 3 seconds)
Inter-green period (I)
The time from the end of the green period of the phase losing right-of-way to the beginning of the green period
Optimum Cycle Length (Co)
The cycle time which gives the least average delay to all vehicles using the intersection
Lost Time (L)
The time which is effectively lost to traffic movement in a phase because of starting delays and the falling-off discharge rate during the amber period
Effective Green Time (G)
The time during the cycle when the traffic flows freely discharge through green aspect at the maximum rate
All red period
A red period between the amber and red-amber shown to all approaches in order to allow vehicles to clear the junction safely before starting the next phase
Instantaneous speed of a vehicle at a point
Average speed while in motion
Overall speed including stop
The highest overall speed
Free Flow Speed
When drivers face no restriction in driving and can maintain their desired speeds
The speed below 85% vehicle move (85th percentile speed)
The speed below 98% vehicle move (98th percentile speed)
The speed below 50% vehicle move (50th percentile speed)
Speed at the highest frequency
It is a range of speed (usually taken in 10 mph or 15 kmph increment)
Upper limit at 85th percentile speed
Lowe limit at 15th percentile speed