SOIL CLASSIFICATION FOR EARTH-MOVING OPERATIONS
Various classifications have been established properly for soil depending on the purposes of earth-moving operations. Generally speaking, however, detailed classifications of soil are not required for the ordinary earth-moving operations.
Rather, attention is required to be given to whether the soil to be handled is of special ores or contains special
clay minerals. Hereinafter is described the knowledge necessary for earth work planning prior to such operations as digging, loading, hauling, pushing (spreading), rolling compaction, etc., on ordinary terrain.
* Data (figures) to be given hereinafter vary largely depending on various operating and environmental conditions. Consequently, before starting the earth work, tests should be conducted to obtain correct data for operations.
Some knowledge of the weight data per unit volume of materials of their major ingredients is important for their handling or hauling in mines, etc.. The specific weight data of some major types of soil and ingredients are given below.
WEIGHT DATA OF MATERIALS
Hauling Performance of Construction Machines
HAULING PERFORMANCE OF CONSTRUCTION MACHINES
INTRODUCTION
"What Model or type of a tractor is most suitable to pull this trailer?" "Is this bulldozer capable of going up this hill while pulling that scraper loaded full?" In order to give explicit answers to these questions, it is necessary to have the right understanding of the hauling performance of vehicles.
For easy understanding, let us explain the hauling performance with the following machine capabilities and
related elements.
(1) The inherent machine capability
(2) Elements limiting the inherent machine capability
(3) Machine capabilities required for earthmoving operations
INHERENT MACHINE CAPABILITY
1. What is the inherent machine capability?
a) Output power
The engine horsepower of a construction machine is the most essential power of those developed by the machine itself. This can be estimated by multiplying one element (traction force) by another element (a travel speed). Accordingly, where the engine of a machine develops a rated power; the smaller the travel speed, the larger the traction force or drawbar pull will be. On the contrary, the larger the travel speed, the smaller the drawbar pull.
b) Gear-shifting
Gear-shifting is effected to determine the optimum drawbar pull and travel speed required for accomplishing a given job. Therefore, a machine has several gears to be selected by shifting for the optimum travel speed.
2. Direct-drive type tractor
The table below gives the drawbar pull and travel speeds of a direct-drive type bulldozer.
The rated drawbar pull is such a traction force that can be developed at the rated engine power and the rated revolutions (rpm). The rated drawbar pull is normally estimated by taking into account the travelling resistance (which will be explained later) and the mechanical loss of power in its line from the engine to the sprockets.
The maximum drawbar pull is the maximum traction force that can be developed by a machine and is estimated from the maximum engine torque. In other words, the maximum drawbar pull of a machine can be developed by the lugging ability of its prime mover and is practically obtained in a low gear. Consequently, the maximum drawbar pull is shown only at F1 on the specifications.
In a TORQFLOW-drive type tractor, the relationships between the travel speeds and drawbar pull are obtained from the combined performance between the engine and the torque converter. In a TORQFLOW-drive machine, it is difficult to relate both the drawbar pull and travel speeds directly to the engine revolutions. Thus, the hauling performance is indicated by curves. The graph at right gives the hauling performance curves of the TORQFLOW-drive type bulldozer.
ELEMENTS LIMITING THE INHERENT MACHINE CAPABILITY
1. What are the elements limiting the inherent machine capability or power? These are;
a) Traction between the undercarriage (tracks or wheels) and the road surface.
b) Altitude
Altitude in b) will be described in a separate issue and herein is examined the problem of traction between the undercarriage and the road surface.
2. Traction between the undercarriage and road surface
"When a motor vehicle cannot be moved due to slipping on the snow-covered road, what should be done to move the vehicle?"
The answers are;
Solution
(1) Add load to the driving wheels.
(2) Install chain to the wheel tires or replace the tires with the spiked type.
(3) Scatter sand or spread straw mats on the road surface.
Reason
(1) The traction force is increased with the added load.
(2) The undercarriage is made so as to develop more traction.
(3) The critical traction force is increased by the higher coefficient of traction.
The above facts can also be applied to a crawler tractor. Now, let us look at the coefficient of cohesion and the critical traction force or traction used in the above table. The critical traction is the maximum traction available depending on the cohesive condition of the road surface. This can be estimated by the following formula.
MACHINE CAPABILITIES REQUIRED FOR EARTHMOVING OPERATIONS.
1. What are the elements limiting the machine capabilities required for earthmoving operations?
When a truck is traveling on the road or going uphill, the following phenomena will be encountered as a matter of course.
Phenomenon
(1) The travel speed of a truck with load on the flat road should vary when the same truck with the same load travels on the rugged or rutted surface.
(2) When traveling on the flat road or going uphill in the same operating gear, the travel speed should vary as a matter of course.
Influential element
(1) Rolling resistance
(2) Grade resistance
2. Rolling resistance
When a vehicle is traveling on the ground or road, the retarding force of ground against wheels or tracks should take place. Such a resistance varies depending on the ground or road surface conditions. The rolling resistance is measured in the ratio to the vehicle weight and can be estimated by the following formula.
Wr = μr•G
Where,
Wr: Rolling resistance (kg)
μr: Coefficients of rolling resistance
G: Vehicle operating weight
The coefficient of rolling resistance can be selected from among those given in the table below, according to the ground or road surface conditions. The coefficient of rolling resistance can be selected from among those given in the table below, according to the ground or road surface conditions.
In a crawler tractor, too, the rolling resistance should vary depending on the type of applied soil. The representative values of rolling resistance, however, are taken into account in preparing the curves for drawbar pull and hauling performance of crawler tractors. Therefore, the varying rolling resistance may practically be ignored.
Conditions
- Uphill traveling
- Traveling on flat, level surface
- Downhill traveling
Haul resistance
- Rolling resistance + grade resistance
- Rolling resistance.
- Rolling resistance – grade resistance
Example (6) What is the hauling resistance against the D60-6 tractor going uphill at 4° in a dry, loose terrain, while pulling an RS08 scraper with maximum load?
Solution:
The gross weight of the RS08 with maximum load is 18870 kg.
The rolling resistance factor is 0.045.
Thus, the rolling resistance is 0.045 × 18870 = 850 kg
The weight of the D60-6 tractor is 12550 kg.
The gross weight of the RS08 is 18870 kg.
Then, the total weight of both machines is 31420 kg
Consequently, the grade resistance is 0.07 × 31420 = 2200 kg.
Thus, the hauling resistance is 850 + 2200 = 3050 kg.
SUMMARY AND APPLICATION
1. Summary
2. Application
Example (7) Assume that the D65 tractor is used to pull a wheeled wagon (the empty weight: 17 tons) with a 50-ton load in a dry, loose terrain. What are the operating gears and the corresponding approx. travel speeds available on a flat, level ground? What is the degree of a hill climbable under the same condition?
Solution:
The rolling resistance
Weight of the wagon (empty): 17000 kg
Payload: 50000 kg
Total weight: 67000 kg
Coefficient of rolling resistance: 0.045
Consequently the rolling resistance against the wagon is 67000 × 0.045 = 3015 kg
TRAFFICABILITY
In general, traffic-ability is indicated by a cone index No. (The method of measuring a cone index No. will be
described later.). The larger the cone index number becomes, the higher the traffic-ability of the machine will become. In other words, on the soil larger in cone index No., a construction machine will be able to travel easier. The minimum cone index numbers required for various types of construction machines to perform digging, hauling operations, etc. are given below.
NOTE:
In determining a cone index, apply the cone penetrometer at 3 or 4 points at least to average the variations in the measured values.
* Cone index numbers (qc)
A cone index number is measured by means of a cone penetro-meter in a cone penetration test.
A rod with a cone at the tip is pushed into the soil by hand.
The pressure required to advance the cone at a slow constant rate is known as the penetration resistance.
The penetration resistance is read out on the dial gauge.
Thereby, the shearing strength of soil can be estimated.
Then, a cone index number can be obtained by referring the estimated shearing strength to the conversion table attached to the meter.