SU1502700A1 - Method of determining deformation properties of soils - Google Patents

Abstract

The invention relates to engineering surveys for construction, in particular, to laboratory and field methods for determining the physical and mechanical properties of soils. The aim of the invention is to increase the test performance of various soils. The method for determining the deformation characteristics of soils includes the stepwise application of a compressive load and its exposure at each step, registration during the process of applying the load in equal increments of sediment, the time of the load from the beginning of its application and determining the stabilized sediment at the time of equality of the relationship between subsequent load times from the beginning of its application to previous. 2 tab.

Description

The invention relates to the field of engineering surveys for construction, in particular to laboratory and field methods for determining the physical and mechanical properties of soils.

The aim of the invention is to increase the productivity of testing various soils.

The method is carried out as follows.

Using a load device, a first compressive load is applied to the ground. Under the action of an applied load step, a sediment of the soil occurs, the value of which is monitored by measuring instruments. After every equal increments of sediment (pudge),

e.g. L5 0.005 mm, record the time of the load step from the beginning of its application. After the first three sequences are obtained, the time of action of the load stage (t, t, and tj) is determined by the equality of the relations between the two and x times of the action of the load from the beginning of its application to the previous ones.

or in general (1)

If this equality does not occur, then at the next increment of the precipitation of soil D8 0.005 mm, the next value of the action time of the load stage t is recorded and the equality

Z

Similarly

The following three sequences of the exposure time value of the load stage are recorded at the same time. As soon as equality is established

t-ntt

on test

the soil is applied to the second load stage and the value of the stabilized soil deposition at the first load step is calculated according to the equation of the secondary consolidation of soils, having the following form /

 one

+ a

In,

tn h

(2)

where ST is the value of stabilized sediment, mm; T - time to stabilize precipitation

soil, h

According to equation (2), it is possible to calculate the amount of soil deposition for any time interval from t to T, i.e. at t pc, the first point of observations of the amount of soil deposition and the corresponding time point of action of the load stage from the beginning of its application at the last (third) observation point, mm and h, a is a constant value calculated from observations of the soil deposition at times t ntt mm.

-P

 -n + l

6 s

h-J..2) 1

(3)

Formula (3) is derived as follows. Differentiating equation (2) get

lz

& t

(four)

where l s h -I

the increment of sediment and the corresponding increment of time of the load stage At (h), mm;

the time of action of the load stage from the beginning of its application, part of the formula (4) for time points and tt,

t D8

tnn thti

- t,

From where the arithmetic mean value-a (formula 3) is found.

T is the time during which the load on the stage of stabilization of the soil is not lysed, h

tcT

t

eleven

,

(6)

where is the time of conditional stabilization of soil, taken depending on the type of the tested soil in accordance with the applicable standards, h:

0.01 L8 is the maximum increment of soil deposition during time t, at which, according to current norms, sludge is considered conditionally stabilized, mm / h.

Formula (6) is derived from equation (2) as follows. Substitute into equation (2) different values of the time of action of the load stage, get

T

Sr 5 „, +

aln

Sr - tor S

t n t

t n "Subtracting the second equation from the first one is obtained.

T

ST -S-r -toT aln

S -s

T

-t

-CT

where exp 35

-c-T

bo - n40

be

45

tt

la and

50

55

five)

i expT- (s7)

those. get the formula (6).

Similarly, stabilized sediment is tested and determined at all stages by compressing the load, and then the deformation characteristics are calculated: deformation modulus and compressibility factor.

An example of a specific implementation of this method for compression testing of solid water-saturated clay with a plasticity number of 21%, a degree of water saturation of 0.98, a moisture content of 17%, a density of 2.17 t / m.

In tab. Table 1 shows the results of observations of the actual sediment of the soil sample (punch sediment) at equal increments of L S 0.005 mm until it stabilizes with a compressive load of 0.1 MPa and the corresponding time intervals of the load from the beginning of its application.

The time t is determined from the beginning of the application of the load stage after which the creep strength prevails during the consolidation process and the sediment is described by the equation of secondary consolidation (2).

The onset of such a moment is determined by condition (1).

To begin with, we take as t t, 3.50 h (Table 1). The next increment of precipitation of the stamp 45 0.005 mm occurred at t 5.35 h, and another one at t. 7.35 hours

t-t-tf

  1.37.

-

--- 1.53; t-f

-I4

These ratios are equal with each other with an accuracy of 10.45%. To establish whether such an error is permissible, a stabilized stamp settlement is calculated.

According to equation (3), the load steps, t and,, are constant for the time intervals of action.

.ff 0,0111 mm.

Equation (6) calculates the time it takes for the stamp to stabilize. Since, in this case, the clay was tested for conditional stabilization, they take a sediment rate not exceeding 0.01 mm per ttt 16 h. T 26.9 h.

According to equation (2), the stabilized settlement of the stamp is calculated.

15 li-iy

In - LIS

0.089 mm.

The actual punch stabilized with the sediment is 0.120 mm. The error in calculating the precipitation at the observation points 13.14 and 15 is 25.8%.

Such an error in the calculation of stabilized stamping precipitation is not permissible; therefore, similar calculations continue to be made for the following observation points 14; 15 and 16, etc.

In tab. 2 shows a comparison of the calculated values of the precipitation of the stamp with the actual ones.

Taking into account the fact that at this stage of the load when determining the deformation 2700

soil characteristics, the error of calculating the precipitation is 10%, in this example we are limited to observation points 17, 18 and 19.

From tab. 2 it follows that in order to obtain such an accuracy of calculating the value of the stabilized stamping of the stamp, the tolerance of the equality

relationship

t n

-

 and should

tn "-i

be no more than 0.5-0.8%.

So in this example

after the 19th observation point, in which 19h, the soil test at this load level can be stopped. Since the actual time for stabilization of the precipitate of the stamp is 57 hours, and when using the proposed method it is 19 hours, the productivity is increased 3 times.

The use of the invention at each step of compressive load reduces test time and improves the accuracy of determining the value of stabilized deformation by taking into account the properties and state of the subjects.

soil and thus improve the performance of the use of various soils and the reliability of the determination of deforming parameters.

Claims (1)

Invention Formula The method of determining the deformation characteristics of soils, including the stepwise application of a compressive load and its exposure at each of the steps, the determination of stabilized sediment and the calculation of the deformation characteristics, characterized in that, in order to improve the performance of testing various soils, at each of the steps during the application of the load through equal the increments of the sediment record the load time from the beginning of its application, and the stabilized draft is determined at the time of equality of relations subsequent load times from the beginning of its application to previous ones. t "in person a 1 Comparison of the calculated values of precipitation stamp with the actual Table 1715 20 T2, 20 0.48 0.0188 40.3 0.110 - 8.3