Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D1/00—Investigation of foundation soil in situ
  • E02D1/02—Investigation of foundation soil in situ before construction work
  • E02D1/022—Investigation of foundation soil in situ before construction work by investigating mechanical properties of the soil

Definitions

• the invention relates to engineering geology surveys carried out in coping with construction projects and has specific reference to a soil-testing method.
• the tests are needed for ascertaining the consolidation pressure, the bulk modulus of the soil and the rate of settlement of the structure. Thy should meet high accuracy requirements, for any error may lead to structural failure or unjustified expenditures on the project.
• the known method is inapplicable in testing deep layers of a soil with a high moisture content, for the test site may become flooded by the water and accessible therefore with difficulty.
• a high moisture content of the soil may also prevent the slab from contacting the tested soil layer uniformly over its entire surface area and lead to inaccurate results. Difficulties are experienced in installing, statically loading the slab and taking its settlement measurements under these conditions.
• the prior-art method is practically of no avail in testing a deep layer of soft soil, for its strength is impaired by its deformation due to a sideways pressure of the soil en mass above the site after the excavation of the pit.
• this method does not involve flooding or weakening of the tested layer and is therefore applicable to testing deep layers with a high moisture content and deep layers of soft soil.
• a fraction of the lower surface of the blade may become disengaged from the tested soil layer so that no iniform blade-to-soil contact-- indispensable as far as accuracy and reliability of the test data are concerned -- will exist in those cases when the blade descendes with each revolution of the shaft through a distance less than the pitch of the blade.
• Such a condition can be brought about when the sum of the forces which oppose the entry of the shaft and blade into the soil is slightlx greater than the sum of the forcess applied in order to effect this entry.
• the resistance which the soil offers to the descending shaft tip the frictional forces coming into play between the soil and the descending shaft and a vertical upward component of the resistance which the soil offers to the cutting edge of the blade.
• Coming under the latter heading are the downward axial force, the weight of the shaft and blade and the pull of the helical blade.
• the principal object of the invention is to provide a soil-testing method conducive to high accuracy and reliability of test data which are achievable by preventing deformation of the tested soil layer under the condition of a uniform contact between the lower surface of the blade and the tested soil layer.
• This object is realized by disclosing a soil-testing method consisting in screwing a shaft with a helical blade at the lower end thereof into the soil so as to deform a layer of soil overlaying one under the test, discontinuing the screwing on reaching the tested soil layer, aapplying a series of static axial loadings of downward direction to the shaft -- whereby each successive loading exceeds the preceding one by the same amount --and measuring the displacements of the shaft in response to the loadings wherein according to the invention an equalizing axial load is applied to the blade through the shaft if the pressure exerted by the soil on the lower surface of the blade, as measured at a depth which is less than that of the tested soil layer by an amount exceeding the pitch of the blade, differs from the pressure of an undisturbed soil column overlaying the blade.
• the pressure sustained by the lower surface of the blade signifies contact between this surface and the soil, and the helical shape of the lower surface of the blade provides for uniformity of the contact which is a further guarantee of accuracy and reliability of the test.
• Figure 1 illustrates the shaft with the helical blade preparatory to testing a soil which is clay
• Figure 2 illustrates the shaft with the helical blade
• Figure 3 illustrates the shaft with the blade at an instant when the blade is at a depth which is less then that of the tested soil layer by an amount exceeding the pitch of the blade;
• Figure 4 illustrates the shaft with the blade in a position when the blade is at the depth of the tested soil layer
• Figure 5 illustrates the shaft with the helical blade in a position preparatory to testing a soil which is fine compacted sand
• Figure 6 illustrates the shaft with the helical blade
• Figure 7 illustrates the shaft with the helical blade at an instant when the blade is at a depth which is less than that of the tested layer by an amount exceeding the pitch of the blade;
• Figure 8 illustrates the shaft with the helical blade in a position when the blade is at the depth of the tested soil layer.
• the disclosed soil-testing method consists in screwing a shaft with a helical blade at its lower end into the soil so as to deform a layer of soil overlaying one under the test. On reach a depth which is less than that of the tested soil layer by an amount exceeding the pitch of the blade, the pressure of the soil coming on the lower surface of the blade is measured. Should this pressure differ from the pressure of an undisturbed soil column overlaying the blade, an axial load equalizing the two pressures is applied to the blade through the shaft.
• the screwing operation is discontinued as soon as the blade is at the depth of the tested soil layer, and a series of static axial loadings of downward direction is applied to the shaft, whereby each successive loading exceeds the preceding one by the same amount, before measuring the displacements of the shaft in response to the loadings.
• a development of the disclosed invention is adapted to test soil which is, e.g., clay.
• soil which is, e.g., clay.
• This layer 1 is schematically confined between dashed lines in Fig. 1.
• the pressure P1(Fig. 1)/ of an undisturbed column of the soil 2 overlaying the blade 4 is 0.4 MPa at the depth L1.
• Another development of the disclosed invention is adapted to test fine compact sand with a density of 2.1 g/cm3.
• a foundation with a width of 10 m is required for erecting a building in this case. Consequently, the depth L9 (Fig. 5) of the soil layer to be tested is approximately 10 m.
• This layer 8 of the soil 9 is schematically confined between dashed lines.
• the pressure P9 (Fig. 5) of the undisturbed column of the soil 9 overlaying the blade 11 is 0.21 MPa at the depth L9.
• the disclosed invention may be of utility in testing the soil founded whereupon will be important structures such as nuclear units of atomic power stations, hydroelectric plants and large industrial buildings.

Landscapes

• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Soil Sciences (AREA)
• Analytical Chemistry (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Paleontology (AREA)
• Civil Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
• Nitrogen And Oxygen Or Sulfur-Condensed Heterocyclic Ring Systems (AREA)
• Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
• Force Measurement Appropriate To Specific Purposes (AREA)

Applications Claiming Priority (1)

Publications (2)

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ID=21617437

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• 1989
  • 1989-03-27 WO PCT/SU1989/000079 patent/WO1990011411A1/ru not_active Application Discontinuation
  • 1989-03-27 JP JP50519189A patent/JPH03505108A/ja active Pending
  • 1989-03-27 BR BR898907456A patent/BR8907456A/pt unknown
  • 1989-03-27 EP EP19890905478 patent/EP0416104A4/en not_active Withdrawn
• 1990
  • 1990-11-26 FI FI905819A patent/FI905819A0/fi not_active IP Right Cessation

Patent Citations (2)

Non-Patent Citations (3)

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