RELATION OF COMPACTION AND OTHER SOIL PROPERTIES TO EROSION RESISTANCE OF SOIL

BY:ARYA RENDI FIRMANA

J1B 008 032

The properties of a soil which govern or dictate its resistance to water erosion are numerous and difficult to understand. Many physical, chemycal and mineralogical properties combine to give a soil its individual characteristics of erosion resistance.

The objective of the study reported in this paper were to determine the effect of campaction and other soil properties on the erosion resistance of the soil.

First, the individual effect of various physical, chemycal, and mineralogical soil properties on the erosion resistance of soil was studied

Secondly, the combined effect of compaction and the various soil properties on the erosive behaviour of soil was

investigated.

EQUIPMENT

Seven Texas soil were chosen for testing. They were select to show various properties cohesion with which the physical, chemycal, and mineralogical properties could be related.

The following soil were use : Amarillo fine sandy loam Houston black clay Reagen silty clay loam Lufkin fine sandy loam San saba clay Lufkin clay ( B-Horizon ) and Lake charles clay

EQUIPMENT

Hydraulic flume, the erosion resistance of the soil

was determine in a 72-ft hydraulic flume which was

2.5-ft wide and 1.33 ft deep. The flume was held at a

constant slope of 0.2 percent. Clear plexiglass sides iun the centre 24-ft

section of the flume permitted visual observation

of the soil during the test.

Sediment sampler, sediment sampler were taken to indicated when soil erosion had begun. A suspended sediment sampler was located at the downstream end of

the test section and consisted of nine vertically spaced sampling tubes. Samples were

wihtdrawn by a siphon arrangement and gave the vertical sediment

distribution in the flume.

PROCEDURESTo obtain comparative values of the erosion resistance of the siol, it was necessary to measure the erosive force acting on the soil when they began to erode. To do this, the tractive force acting on the soil for each flow rate was determine. The tractive force is simply the shear force exerted on the soil by the following water. It is expressed by the product of the slope of the energy gradient and the unit weight of water.

PROCEDURES

Preparation of soil samples

Physical soil testHydraulic test

Preparation of soil samples

Before the soils were tested in the hydraulic flume they were passed trough a 0.2 in, screen. They were then loosely places in the 18-ft test section where they were leveled to a depth slightly higher then the concrete slabs ubstream and downstream from the tes section . This was to allow for settling after wetting. No attempt was made to compact the soil for the first test. The soil was then wetted and allowed to drain for approximately 20 to 24 hr before the hydraulic tests were begun.

Hydraulic tests

The actual hydraulic test procedure consisted of increasing the flow rate by small increments until the soil began to erode at a visable high rate. After each

increase and when the flow had stabilized, sediment samples were taken and the

instrument reading recorded to determine the tractive force. After the soil began

erodin, the flow was increased and additional three to four times to make

certaint complette bed failure had occurred. The actual point at which the bed failed was determine letter by analyzing the

sediment samples obtained during the tests. At the end of the test, replicated soil

samples were taken from the bed to determine the void ratio, which indicated

the degree of soil compaction exiting.

Physical soil tests

The physical tests of the soil were ferformed in accordance with the procedures of the American Society of Testing Materials and with procedures outlined in the Texas A&M University Soil Physics

Laboratory Procedures. The following physical properties were obtained: the percent clay, the

mean particle size, the disperation ratio, the vane shear streangth, and the plasticity index.

DISCUSSION of DATA AND RESULT

The rate at which the channel was eroding during each test was calculated from the concentration of the sediment samples and the rate of flow. The erosion rates were expressed as pound of soil eroded per minute per foot of flume width. The critical tractive force for each test was determined by plotting the channel erosion or degradation rate indicated by both sediment samplers versus the corresponding tractive force. The degradation rate was observed to increase linearly at a very slow rate up to a point. Above this point it increased rapidly with increasing value of tractive force.1. Effect of compaction on erosion resistance of soil.2. Effect of various soil properties on erosion resistance of soil.3. Combined effect of compaction with various soil properties

on erosion resistance of soil

SUMMARY

If we are to protect our soil against water erosion, it is essensial to find the soil propertise which can most accuratly be use in determining the erosion resistance of a soil for any given soil condition. One important condition of a soil which is always subject to change is the degree of compaction. In this study the erosion resistence of Seven Texas soil was determined in a hydraulic flume and was related to various soil properties. Each soil was tested at three degrees of compaction, at three values of void ratio.

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