Highway Research Board Special Report 

About: Highway Research Board Special Report is an academic journal. The journal publishes majorly in the area(s): Soil water & AASHO Road Test. Over the lifetime, 420 publications have been published receiving 8839 citations.

On kinetic waves, II . A theory of traffic flow on long crowded roads

Abstract: This paper uses the method of kinematic waves, developed in part I, but may be read independently. A functional relationship between flow and concentration for traffic on crowded arterial roads has been postulated for some time, and has experimental backing (§2). From this a theory of the propagation of changes in traffic distribution along these roads may be deduced (§§2, 3). The theory is applied (§4) to the problem of estimating how a ‘hump’, or region of increased concentration, will move along a crowded main road. It is suggested that it will move slightly slower than the mean vehicle speed, and that vehicles passing through it will have to reduce speed rather suddenly (at a ‘shock wave’) on entering it, but can increase speed again only very gradually as they leave it. The hump gradually spreads out along the road, and the time scale of this process is estimated. The behaviour of such a hump on entering a bottleneck, which is too narrow to admit the increased flow, is studied (§5), and methods are obtained for estimating the extent and duration of the resulting hold-up. The theory is applicable principally to traffic behaviour over a long stretch of road, but the paper concludes (§6) with a discussion of its relevance to problems of flow near junctions, including a discussion of the starting flow at a controlled junction. In the introductory sections 1 and 2, we have included some elementary material on the quantitative study of traffic flow for the benefit of scientific readers unfamiliar with the subject.

Landslide types and processes

Abstract: THE WHOLE RANGE OF EARTH MOVEMENTS THAT MAY PROPERLY BE REGARDED AS LANDSLIDES IS REVIEWED AND THESE MOVEMENTS CLASSIFIED ACCORDING TO FACTORS THAT HAVE SOME BEARING ON PREVENTION OR CONTROL. THE TERM LANDSLIDE IS DEFINED AS DENOTING DOWNWARD AND OUTWARD MOVEMENT OF SLOPE-FORMING MATERIALS COMPOSED OF NATURAL ROCK, SOILS, ARTIFICIAL FILLS, COMBINATIONS OF THESE MATERIALS. THE MOVING MASS MAY PROCEDE BY ANY ONE OF THREE PRINCIPLE TYPES OF MOVEMENT: FALLING, SLIDING, OR FLOWING, OR BY THEIR COMBINATIONS. MATERIALS ARE CLASSED, FOR FALLS AND SLIDES, INTO BEDROCK AND SOILS. LANDSLIDES ARE CLASSIFIED BY TYPES OF MOVEMENT, BUT IT MUST BE REMEMBERED THAT A RIGID CLASSIFICATION IS NEITHER PRACTICAL NOR DESIREABLE. VARIATIONS IN THE TYPE OF MOVEMENT AND IN THE MATERIALS VARY FROM PLACE TO PLACE, OR FROM TIME TO TIME, IN AN ACTUAL LANDSLIDE. SLUMPS AND SLUMPS COMBINED WITH OTHER TYPES OF MOVEMENT, MAKE UP A HIGH PROPORTION OF THE LANDSLIDE PROBLEMS FACING THE HIGHWAY ENGINEERS. THE MOVEMENT IN SLUMPS TAKES PLACE ONLY ALONG INTERNAL SLOPE SURFACES. SOME OF THE COMMON VARIETIES OF SLUMP FAILURE ARE ILLUSTRATED IN A FIGURE. THE PROCESS OF LANDSLIDING IS ESSENTIALLY A CONTINUOUS SERIES OF EVENTS FROM CAUSE TO EFFECT. IN MANY INSTANCES THE PRINCIPLE CAUSE OF THE SLIDE CANNOT BE REMOVED SO IT MAY BE MORE ECONOMICAL TO ALLEVIATE THE EFFECTS CONTINUALLY OR INTERMITTENTLY WITHOUT ATTEMPTING TO REMOVE THE CAUSE. LANDSLIDES GENERALLY TAKE PLACE UNDER THE INFLUENCE OF GEOLOGIC, TOPOGRAPHIC, OR CLIMATIC FACTORS COMMON TO LARGE AREAS. VERY SELDOM CAN A SLIDE BE ATTRIBUTED TO A SINGLE DEFINITE CAUSE. ALL TRUE SLIDES (EXCLUDING FALLS) INVOLVE THE FAILURE OF EARTH MATERIALS UNDER SHEAR STRESS. THE INITIATION OF THE PROCESS CAN THEREFORE BE REVIEWED ACCORDING TO: (1) THE FACTORS THAT CONTRIBUTE TO HIGH SHEAR STRESS, AND (2) THE FACTORS THAT CONTRIBUTE TO LOW SHEAR STRENGTH. THE PRINCIPLE FACTORS CONTRIBUTING TO THE INSTABILITY OF EARTH MATERIALS ARE: (1) REMOVAL OF LATERAL SUPPORT LEADING TO INSTABILITY AND ACTIONS OF EROSION, GLACIER ICE, WAVES AND LONGSHORE OR TIDAL CURRENTS; CREATION OF NEW SLOPE BY PREVIOUS ROCKFALL, SLIDE, SUBSIDENCE, OR LARGE SCALE FAULTING, AND HUMAN AGENCIES, (2) SURCHARGE WHICH INCLUDES NATURAL AND HUMAN AGENCIES, (3) TRANSITORY EARTH STRESSES WHICH MAY RESULT FROM EARTHQUAKES, VIBRATIONS FROM BLASTING, MACHINERY, AND TRAFFIC, (4) REGIONAL TILTING WHICH CAUSES PROGRESSIVE INCREASE IN SLOPE ANGLES, (5) RE- MOVAL OF UNDERLYING SUPPORT BY UNDERCUTTING OF BANKS, BY RIVERS AND WAVES, SUBAERIAL WEATHERING, SUBTERRANEAN EROSION, HUMAN AGENCY, SUCH AS MINING, AND (6) LATERAL PRESSURE DUE TO WATER IN CRACKS AND CAVERNS, FREEZING OF WATER IN CRACKS, AND SWELLING. FACTORS THAT CONTRIBUTE TO LAW SHEAR STRENGTH ARE DISCUSSED.

Some temperature effects on soil compressibility and pore water pressure

Abstract: DATA ARE PRESENTED TO SHOW THAT HEATING A COHESIVE SOIL INCREASES ITS COMPRESSIBILITY AT LOW LEVELS OF APPLIED STRESS AND ALSO PRODUCES VOLUME DECREASES. THE VOLUME CHANGES ASSOCIATED WITH TEMPERATURE INCREASES ARE SHOWN TO BE RELATED TO THE DEGREE OF OVER-CONSOLIDATION OF THE SOIL, DECREASING AS THE OVERCONSOLIDATION RATIO INCREASES. COOLING THE SOIL ALTERS ITS STRESS-STRAIN CHARACTERISTICS AND CAUSES IT TO BEHAVE AS IF IT WERE OVER-CONSOLIDATED. SECONDARY COMPRESSION RATES ARE SHOWN TO BE AFFECTED ONLY SLIGHTLY BY HEATING AND SIGNIFICANTLY BY COOLING. TEMPERATURE-INDUCED PORE WATER PRESSURES IN UNDRAINED TRIAXIAL SPECIMENS ARE SHOWN TO BE RELATED TO THE STRESS HISTORY OF THE SPECIMEN AND, FOR SOME MATERIALS, PREDICTABLE FROM THE RESULTS OF TRIAXIAL CONSOLIDATION TESTS. /AUTHOR/

Thermal Properties of Soils

Abstract: CALCULATION OF DEPTH AND RATE OF FROST PENETRATION OR DEPTH AND RATE OF THAW OF FROZEN SOILS REQUIRES A KNOWLEDGE OF THE THERMAL PROPERTIES OF SOILS. THESE PROPERTIES INCLUDE THERMAL CONDUCTIVITY, SPECIFIC HEAT AND VOLUMETRIC HEAT CAPACITY, AND THERMAL DIFFUSIVITY. DEFINITIONS ARE PRESENTED OF THESE TERMS, WITH THE UNITS USED IN THE PAPER. THE IMPORTANT ASPECT OF TEMPERATURE ON THE THERMAL CONDUCTIVITY OF SOIL IS WHETHER THE SOIL IS FROZEN OR NOT. THE DIFFERENCE IN CONDUCTIVITY OF FROZEN AND UNFROZEN SOILS IS CHIEFLY DEPENDENT ON MOISTURE CONTENT. TESTS HAVE SHOWN THAT AN INCREASE IN THE DRY DENSITY OF A SOIL, THE PERCENTAGE OF MOISTURE REMAINING THE SAME, RESULTS IN AN INCREASE IN THERMAL CONDUCTIVITY. IF SOILS OF DIFFERENT TEXTURE ARE TESTED AT EQUAL MOISTURE CONTENTS AND DENSITIES IT WILL BE FOUND THAT THE COARSE-GRAINED MATERIALS, SUCH AS GRAVELS AND SANDS,WILL HAVE HIGH CONDUCTIVITY; FINE-GRAINED SOILS SUCH AS SILT LOAMS AND CLAYS, LOW CONDUCTIVITY; AND INTERMEDIATE-TEXTURED SOILS VALUES BETWEEN THESE TWO. DIFFUSIVITY VALUES ARE OF INTEREST IN FROST CALCULATIONS SINCE THEY INDICATE THE RATE AT WHICH A SOIL WILL CHANGE TEMPERATURE WHEN THE TEMPERATURE OF THE SURROUNDING MEDIUM CHANGES. IN CALCULATIONS INVOLVING THE FREEZING OR THAWING OF A SOIL IT IS NECESSARY TO TAKE INTO ACCOUNT THE LATENT HEAT OF FUSION OF THE ICE. NUMERICAL VALUES OF THE VARIOUS CONSTANTS PERMIT MATHEMATICAL CHECKS OF VARIOUS HEAT-TRANSFER PROBLEMS IN CONNECTION WITH FROST ACTION IN SOILS. THE NUMERICAL VALUES OF SPECIFIC HEAT AND THERMAL CONDUCTIVITY PRESENTED WITH WHICH DIFFUSIVITIES MAY ALSO BE CALCULATED, ARE OFFERED FOR USE IN SUCH CALCULATIONS.