Description:4. DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to modified correlation of shear strength parameters of coarse and fine grained soils based on SPT (N1)60.

BACKGROUND OF THE INVENTION

Standard penetration test (SPT) is an in-situ dynamic penetration test designed as an indicator of the density and compressibility of granular soils. It is also commonly used to check consistency of stiff or stony cohesive soils.

Standard penetration test is conducted by means of the standard split spoon, furnishes data about resistance of the soils to penetration which can be used to evaluate standard strength data, such as N values (number of blows per 30 cm of penetration using standard split spoon) of the soil. The advantages of test is that it is being carried out in routine exploration borehole of varying diameter and its ability to give other geotechnical properties which may be related to crude but straight forward empirical design rules.

Common Soil Groups: The strength characteristics of natural soils are strongly influenced by the geologic processes of soil formation. Hence it is possible to identify strength characteristics that are common to soils within broadly defined groups. Groups with well-defined characteristics include saturated cohesion less soils, soft saturated cohesive soils, and heavily over consolidated clays etc.

Saturated cohesion less soils: The value of Phi  ranges from about 27 to 45° or more and depends on several factors. For a given soil the value of  increases as relative density increases. For different soils at same relative density, the value of  affected by particle size distribution and particle size. The value of  for a well graded soil may be several degrees greater than that for a uniform soil of the same average particle size and shape. The same is true when a soil composed of angular grains is compared with one made up of rounded grains. The effect of moisture on phi is small and amounts to no more than 1 or 2 ° (Lambe and Whitman 1969, 147-149; Holtz and Kovacs 1981; 514-519).

For every civil engineering Stable structure such as building, bridge, highway, tunnel, dam and towers, a proper foundation soil is necessary. Then for successful evaluation of the suitability of that soil to construct a safe foundation and as construction materials, information about its properties is frequently necessary. Therefore, understanding soils detailed geotechnical, physical, and engineering properties are very much essential.

In the last decade many researchers were performed to correlate the physical properties with the mechanical properties. This approach was adopted for the purpose of time saving and reduces cost of investigations. In addition, it was carried out by the earlier researchers in the field of soil mechanics and foundation engineering.
These correlations were brought out specific to the researcher’s findings in specific geological areas. So, considering the same in general for any construction site needs caution.

Bridge and railway projects are aimed for 100-year period. So, the structures constructed should be so designed keeping in mind. Nowadays the climate change has brought tout many challenges specially for hydro and geotechnical soil formations and sudden changes in soil strata due to flash floods, drought, sudden lowering of water table etc. hence Geotechnical design should be done considering these points and hence the basic shear parameters c and Phi should be very carefully chosen in case, they are not arrived from lab tests.

Thus, there is a need for determination of modified correlation of shear strength parameters of coarse and fine grained soils based on SPT (N1)60.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key or critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

One object of the invention is todetermine a method for modified correlation of shear strength parameters of coarse and fine grained soils based on SPT (N1)60.

Another object of the invention is to reduce the discrepancy between correlated values of soil shear strength parameters based on site SPT N values and actual laboratory test results.

According to one aspect of the present invention, the correlated Phi value (N1)60 values equal to or more than 100 are very high and need to be limited to a certain maximum value. The correlation is used for all granular soil types with majorly fine sand. The phi value of SM soils is influenced by percentage of particles of sand, and gravel present, as well as in-situ density and (N1)60.

The invention may also relate to any alternative methods or processes comprising any combination of the above or below features within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein:

FIG. 1 illustrates relationship between  and N from IS 6403-1981 Fig 1.

FIG. 2 illustrates relationship shear strength, plasticity index and SPT N value from Stroud (1975).

FIG. 3 illustrates relationship between SPT (N1)60 and  values for SM soils with gravel less than 15 % and SPT (N1)60 values<60 with in situ density range 17-20 kN/m3.

FIG. 4 illustrates relationship between SPT (N1)60 and values for SM soils with SPT (N1)60 values>60 and gravel % less than 10 with in situ density range-21.5-22.5 kN/m3.

FIG. 5 illustrates relationship between SPT (N1)60 and  values for SC Soil with SPT (N1)60 values according to one embodiment of the invention.

FIG. 6 illustrates relationship between C value and SPT (N1)60 values Clayey soil with SPT (N1)60 values according to one embodiment of the invention.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present invention in any way.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the present disclosure is not limited in its application to the details of composition set forth in the following description. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

According to one embodiment of the invention, the present invention relates to determination of modified correlation of shear strength parameters of coarse and fine grained soils based on SPT (N1)60.

SPT is an in-situ dynamic penetration test designed as an indicator of the density and compressibility of granular soils. It is also commonly used to check consistency of stiff or stony cohesive soils.

Standard penetration test is conducted by means of the standard split spoon, furnishes data about resistance of the soils to penetration which can be used to evaluate standard strength data, such as N values (number of blows per 30 cm of penetration using standard split spoon) of the soil. The advantages of test is that it is being carried out in routine exploration borehole of varying diameter and its ability to give other geotechnical properties which may be related to crude but straight forward empirical design rules.

For this purpose, SPT N values of 40 boreholes along with laboratory test data were collected from an ongoing project of Ministry of Railways, India. The entire procedure can be performed in two steps. Firstly, doing a literature survey including different relevant standards and correlations given in these will be used to estimate the values of followed by a comprehensive evaluation of correlated values based on actual laboratory test results, and finally, determination of modified correlation ofphi values of soils to be considered for design. For this purpose, different regression techniques including linear, multiple, and polynomial regression will be used. Finally, modified correlation between shear strength parameters of soil and SPT N value will be proposed and evaluated for obtaining reliable shear parameters for design.

Around 40 Boreholes of 20 bridges with alternated fine and granular soil layers considered. The phi value from lab data is presented. Lab data is not available for dense silty sand and clayey soils with high SPT (N) values. It is very difficult to collect UDS samples of such soils with high SPT N values. Moreover, any lab test conducted on remolded samples may not give appropriate results which represent the actual sub soil conditions. In such cases the designer must use certain correlations in line with codal provisions as well as methods accepted in global practice to evaluate the shear parameters from available data such as gradation of soil, plasticity index and SPT N value. In this research the shear parameters (phi value and C value) obtained from correlations are compared with available lab data to arrive at more accurate and realistic and reliable values of shear parameters for design of shallow and deep foundations.

According to one embodiment, in the present invention, 40 boreholes from 20 bridge structures are considered for comparing the phi values of correlation with the lab/experimental values from BH data summary. The boreholes are of 30-40 depth and the soil strata is of alternate layers of C-Phi soils. Correlation given using Eqn 1 & 2 used for estimating Phi value. In this study, Regression analysis and mathematical error correction is used for predicting error reduction.

Further, thorough evaluation has been done on usage of certain interpretations for estimation of design shear parameters for SM (SP-SM) & SC Soils and CL, CI & CH soils based on available SPT (N) Values and laboratory (gradation and Atterberg limits) data and comparing the same with available GTI data (shear data from Lab Results) pertaining to the design of shallow and pile foundations.

Thorough evaluation of the available lab data and correlations was required for arriving at the shear strength parameters for SM Soil and SC soils (i.e., Phi- angle of friction) and CL, CI & CH soil (i.e., C value) to be considered in the absence of laboratory shear test results.

Shear Strength is the principal Engineering property which controls the stability of soil mass under loads. It governs the bearing capacity of soils, the stability of slopes in soils, the earth pressure against retaining structures and many other problems. Unfortunately shear strength is the most complex Engineering properties of soils. The current research – brings out the estimation of geotechnical design shear parameters for Granular soil based on available field (SPT N values, (N1)60 values) and laboratory (gradation and Atterberg limits) and comparison with available lab data with shear parameters for similar soil data pertaining to the design of shallow and pile foundations.

The characteristic shear strength parameters of soil are obviously decisive for the geotechnical design. Characteristic parameters are defined as cautious estimates of the soil parameters affecting the limit state. It is shown how geotechnical engineers interpret this cautious estimate. Due to the inherent lack of data in geotechnical investigations there is always a certain degree of subjectivity in assessing the characteristic soil parameters. The range of characteristic shear parameters assigned to the same set of laboratory experiments by 90 geotechnical engineers has been used to design a spread foundation. The resulting geometrical dimensions are remarkably different. It is concluded that geotechnical calculations are rather estimates than exact predictions. Thus, for intricate geotechnical projects a sensitivity analysis should be performed to find out critical scenarios. Furthermore, a continuous appraisal of the soil properties during the construction process is indispensable.

Data obtained from BH at 20 bridge locations of a railway project in Gujarat is considered for present study. The stratification of Gujarat soils at these locations has alternate layers of granular soil to cohesive fine grain soil layers alternately.

The SPT N value of granular soil layers picked and SPT (N1)60 calculated by applying the correction factors and the corresponding phi angle from lab data is also noted. Different correlations for calculation of Phi angle are presented in the below section. But here in our current study the phi angle using correlations inEqn 1& 2 is calculated and compared with lab data. It is noticed that lab value of Phi is lower compared to the value obtained from correlations.

The study indicated that the angle of internal friction phi of granular soil type (SM & SC) calculated from correlations from SPT (N1)60Value with Eqn 1 & 2 gives a higher value when compared to the values obtained from lab tests.

Presentation of empirical equations for estimating engineering properties of soils is a simple, low cost and widely used method. One of the major concerns in using these equations is evaluating their accuracy in different conditions and regions which often lead to doubts about obtained results. Most of these equations were derived in special laboratories, different climate conditions and in soil with different geotechnical and geological engineering properties and were generalized to other conditions. The main question is that whether these methods are also applicable to other conditions. Using local equations and narrowing the usage range of various methods based on each region’s properties are appropriate methods to solve these problems. This leads to simplified and faster analysis and high reliability in the obtained results. In this paper, modification, by applying correction factor to Phi values and C values obtained from empirical equations derived from SPT (N1)60 is arrived. The shear parameters (phi values& C values) from empirical equations are compared with Shear parameters (Phi values& C values) obtained from lab tests of 40 Boreholes conducted for 20 Bridge locations in Gujarat region.

Existing correlations using SPT N values:

Granular soils using SPT N values and index properties: According to one embodiment, Fig 1 is 6403 1981 phi value can be obtained using SPT (N) Value N>30 -  is 36° and N>50  is 40°.Correlations of SPT blow counts to cohesion less soil friction angle and unit weight follow Bowles (1977) and are consistent with many of the NHI manuals used by the department.

The correlations use SPT (N) values corrected by overburden and hammer efficiency (N1 (60))
• Use the max value for GW
• Use the avg for GM and SP
• Use the minimum for SC
• Use the minimum+0.5 for ML
• Use the avg +1 for SW
• Use the avg -1 for GW
• Use the maximum -1 for GP

• Wayne C Teng:Engr properties of Granular soils in book “Foundation Design” internal angle of friction  for fine sand with silt is calculated using Meyerhof correlation.

•  = 25 + 0.15 Dr (%) for granular soil with more than 5% fine sand and silt – Eqn (1)

•  = 30 + 0.15 Dr (%) for granular soil with less than 5% fine sand and silt. – Eqn (2)

• Where Dris relative density, which can be estimated using the formula suggested by Skempton (1986) as given in Eqn 9.5 in book “site Investigations” by CRI Clayton, MC Matheews& NE Sinus.

• Dr(%) = 100 X SQRT(N1(60)/60)
• By using Eqn (1) for SPT (N1)60 range 10-70 angle of friction  ranges from 31 to 40°

• By using Eqn (2) for SPT (N1)60 range 10-70 angle of friction  ranges from 36 to 46°

Typical values of the effective angle of shearing resistance of compacted clays.
Soil description Class* φ′ (°)
Silty clays, sand‐silt mix SM 34
Clayey sands, sand‐clay mix SC 31
Silts and clayey silts ML 32
Clays of low plasticity CL 28
Clayey silts, elastic silts MH 25
Clays of high plasticity CH 19

Table 1: effective angle of shearing resistance

FIG. 2 illustrates relationship shear strength, plasticity index and SPT N value according to one embodiment of the invention. The phi value of SM soils is influenced by several variables, including the percentage of particles of sand, and gravel present, as well as in-situ density and (N1)60.

Correlations for fine grained soils Stroud (1975) has established empirical correlations between SPT N value and undrained shear strength. The graph of same is represented in Fig-1.
Cu (kPa) = f1 (N1)60
Where,
f1 = Factor depending on Plasticity Index to be taken from Fig-2
N60 = SPT N value measured based on a system which is to 60% efficient.

The phi values acquired via correlations cannot be utilized directly since they are overstated, as shown by the graphs, which show that they are greater than the phi values obtained from lab tests for SM & SC soils and CL,CI& CH soils. Therefore, various limiting criteria should be gathered and compared based on the local soil data and nearby boreholes. However, since this step is omitted in this case and Phi values are adopted immediately, an effort has been made to produce a modified correlation that incorporates a reasonable correction factor to the current correlation.

As a result of their dependence on factors such as soil gradation, density, confining pressure (depth from EGL), and fines percentage, the results obtained from lab tests are not clearly defined and are dispersed. The same can be inferred from below interactive chart (fig 3, 4, 5 & 6). However, the graph shows that a variety of phi values exist. The graph shows the range of curved lines where the value of Phi falls. The graph may be used to determine (see) the range for a specific (N1)60value.Firstly, the data is segregated as 2 parts as most of the data has medium to fine grained sand.

According to one embodiment of the invention, correlated data's percent error (average error) is approximated. By multiplying the accuracy percentage (%) (100-avg error percentage (%)) by the correlation, one may derive the modified correlation correction to the correlated phi value. The same produced average errors that were under 2% and individual data errors that were under +/-3.5%. For example the average percentage inaccuracy found in case 1 (SM Soil) is 8.7%. i.e., the associated values are 8.7 % greater than the lab values. But to decrease the individual mistake the correlation value is multiplied by 0.9i.e accuracy is 90% to give the adjusted correlation value to consider for design to reduce the design error. The average inaccuracy is now within 1.0%, whereas the individual error ranges from -7.0% to +3.64%.

Case 1: SM Soil with SPT (N1)60<60 and Gravel <15% Density range 17-20kN/m3
(N1)60 Density (kN/m3) Gravel Sand Silt &
Clay Lab Phi value Correlation Phi value % Error Modified correlation Phi value (corr*0.9) % Error after correction
28 20.30 0 87 13 32 35 9.38 31.5 -1.56
19 17.36 0 63 37 30 33 10.00 29.7 -1.00
17 16.97 2 54 44 0 32 6.67 28.8 -4.00
46 17.46 3 77 20 33 38 15.15 34.2 3.64
49 17.27 1 74 25 34 38 11.76 34.2 0.59
10 17.27 12 53 35 30 31 3.33 27.9 -7.00
24 17.27 7 62 31 30.5 34 11.48 30.6 0.33
53 17.87 7 59 34 35 39 11.43 35.1 0.29
59 17.87 1 55 44 7 39 5.41 35.1 -5.14
60 17.87 4 71 25 37 40 8.11 36 -2.70
55 17.27 0 68 32 36 39 8.33 35.1 -2.50
55 17.27 4 64 32 36 39 8.33 35.1 -2.50
33 17.38 0 75 25 32 36 12.50 32.4 1.25
26 17.21 12 77 11 32 34 6.25 30.6 -4.38
50 17.21 0 73 27 34 38 11.76 34.2 0.59
56 17.46 0 84 16 0 39 14.71 35.1 3.24
53 17.46 1 76 23 0 39 14.71 35.1 3.24
Avg Error (%) 8.70 Avg Error (%) after correction -1.04

Table 2: SM Soil with (N1)60<60 and Gravel <15% Density range 17-20kN/m3

According to one embodiment, in this instance, the average percentage error obtained is 8.7%, meaning that the associated values are 8.7% higher than the lab values. (N1)60<60, Density range 17-20.3kN/m3, However, to get the adjusted correlation value, the correlation value is multiplied by 0.9in order to lower the individual error. To reach the adjusted correlation value, the average error is now within -1.04% and the individual error ranges from -7.0% to +3.64%.

Case 2: SM Soil with SPT(N1)60>60 and Gravel <10% Density range 21.5-22kN/m3
(N1)60 Density (kN/m3) Gravel Sand Silt &
Clay Lab Phi value Correlation Phi value % error Modified correlation Phi value (corr*0.87) % error after correction
100 22.2 0 91 9 35 40 14.29 34.80 -0.57
100 22.1 1 75 24 35 40 14.29 34.80 -0.57
100 22.1 0 87 13 36 40 11.11 34.80 -3.33
100 22 1 84 15 35 40 14.29 34.80 -0.57
100 22.1 0 86 14 36 40 11.11 34.80 -3.33
89 22.3 0 88 12 36 40 11.11 34.80 -3.33
100 21.8 0 88 12 35 40 14.29 34.80 -0.57
100 22 0 79 21 35 40 14.29 34.80 -0.57
Avg Error (%) 13.09 Avg Error (%) after correction -1.60

Table 3: SM Soil with (N1)60>60 and Gravel <10% Density range 21.5-22kN/m3

In this instance with SM soils with N>60 and Density range 22-22,3kN/m2, the average percentage error obtained is 13.09%, meaning that the associated values are 13.09% higher than the lab values. (N1)60>60, Density range 21.5-22.2 kN/m3, However, to get the adjusted correlation value, the correlation value is multiplied by 0.87 in order to lower the individual error. To reach the adjusted correlation value, the average error is now within -1.6% and the individual error is within -3.33%.

Case 1: SC Soil with (N1)60 <25-60 and Density range20.5-22.2kN/m3
(N)160 Density (kN/m3) Gravel Sand Silt &
Clay Lab Phi value Correlation Phi value % Error Modified correlation Phi value (corr*0.87) % Error after correction
49 22 0 79 21 34 38 11.76 33.06 -2.76
28 21 16 59 25 31 35 12.90 30.45 -1.77
29 22 2 61 37 34 35 2.94 30.45 -10.44
31 21 0 54 46 29 35 20.69 30.45 5.00
42 21 3 62 35 31 37 19.35 32.19 3.84
60 21 2 72 26 33 40 21.21 34.80 5.45
47 21 0 71 29 32 38 18.75 33.06 3.31
43 20 8 61 31 31 37 19.35 32.19 3.84
50 21 0 78 22 33 38 15.15 33.06 0.18
Avg Error (%) 15.79 Avg Error (%) after correction 0.74

Table 4: SC Soil with (N1)60 <25-60 and Density range20.5-22.2kN/m3

Data error correction follows the same process as is done for SM soils. The associated values are 15.79% higher than the lab values, which has an average percentage error of 15.79%. However, to get the adjusted correlation value, the correlation value is multiplied by 0.87 in order to lower the individual error. The average error is now within 0.74%, while the individual error is between -10% and +5%.

Case 2: SCSoil with (N1)60 Range 60 -100and Density range21.2-22.2kN/m3
(N1)60 Density (kN/m3) Gravel Sand Silt &
Clay Lab Phi value Correlation Phi value % Error Modified correlation Phi value (corr*0.85) % Error after correction
100 22 6 88 6 36 40 11.11 34.00 -5.56
100 22.1 19 61 20 34 40 17.65 34.00 0.00
100 21.2 0 85 15 33 40 21.21 34.00 3.03
100 21.5 10 75 15 34 40 17.65 34.00 0.00
70 21.4 5 76 19 33 40 21.21 34.00 3.03
79 21.3 0 85 15 33 40 21.21 34.00 3.03
Avg Error (%) 18.34 Avg Error (%) after correction 0.59

Table 5: SC Soil with (N1)60 Range 60 -100and Density range21.2-22.2kN/m3

According to one embodiment of the invention, the associated values are 18.34% higher than the lab values, which is the average percentage error found. However, to get the adjusted correlation value, the correlation value is multiplied by 0.85 in order to lower the individual error. The average error is currently0.59%, while individual error ranges from -5% to +3%. The Phi value may be derived by utilizing this adjusted correlation value and employed in the geotechnical design of open and pile foundations.

The correction factor to the correlated value to obtain a reliable angle of shearing resistance can be arrived as represented below for SM & SC soils which can be used in future where lab data is not available.
S. No Soil Type (N1)60 range Gravel % Density range Correction factor for correlation value
1 SM Soil 0-60 0-15 18-20 0.9
2 SM Soil 60-100 0-15 21.8-22.2 0.87
3 SC Soil 25-60 0-16 20.5-22.2 0.87
4 SC Soil 60-100 0-16 21.2-22.2 0.85

For Fine Grained Soils -SPT (N1)60 value is calculated from SPT N value by applying the correction factors. The f1 value from graph is obtained from Plasticity index of soil and C value is calculated from the above correlation. The soil data from almost 40 boreholes of 20 Bridge Structures of a railway project in Gujarat are considered. The soil consisted of alternate layers of granular and cohesive soils. SPT (N1)60 value is calculated using the SPT N value and soil data from Bore holes by applying correction factors. CL, CI & CH soils are considered for this study. Table with “C” values considered from lab tests and “C” value calculated from correlations using SPT (N1)60 and Plasticity Index is given below.

According to one embodiment of this invention, Graphs are drawn with “C” value on X-axis and SPT (N1)60 on Y- axis. As can be seen from graph, the “C” values are almost similar i.e with almost 5-10% variation till SPT (N1)60 is 60. But after that i.e SPT (N1)60> 60 the “C” value from correlations is higher than the “C” values from lab tests. As per data from the lab tests and correlations as inferred from graphs (fig 6) it is noticed that till SPT N value of 100 the C value is within 300. So a limiting “C” value of 300 kN/m2should be considered. Further if SPT N value is more than 100 i.e refusal, “maximum C” value from lab tests is around 450-500 kN/m2. Hence the maximum C value calculated from correlations should be limited to 500kN/m2for SPT N>100. Further the f1 value (obtained from Plasticity index) should be limited to a maximum value of 6. “C” value should be limited to a maximum of 500kpa for SPT N>100 and 300Kpa for SPT N value <100.

The average error percentage of C value from correlations compared to lab value till SPT (N1)60 <60 is 1.2% which is negligible. But as SPT (N1)60 value ranges between 60-100, the error percentage between correlation and Lab value is almost 13.2%. So this error needs to be corrected to obtain reliable C values for design. The approach of limiting the values of shear parameters obtained from empirical correlations may at times yield to conservative values.

If the lab data at the adjacent boreholes with relevant depth, soil properties and soil type is available, the same can adopted in design instead of calculating it by correlation or correlated value should be compared and lower value should be adopted.

Depth N Soil (N1)60 PI f1 Cohesion Lab Data kN/m2 Cohesion Correlated value kN/m2
0.5 14 CL 9 12 6 48 54
3 7 CL 5 8 6 31 30
9 27 CI 21 22 5.2 141 109
12 42 CI 34 24 4.9 213 167
15 43 CI 34 28 4.5 220 153
18 36 CL 29 19 5.6 143 162
21 40 CL 32 9 6 163 192
0.5 8 CL 5 16 6 49 30
3 11 CL 7 14 6 51 42
9 22 CI 17 27 4.6 117 78
12 28 CI 23 25 4.8 152 110
15 45 CI 36 29 4.4 234 158
18 35 CL 28 18 5.8 159 162
21 60 CL 48 14 6 298 288
24 65 CL 52 14 6 316 312
0.5 9 CL 6 9 6 41 36
3 11 CL 7 8 6 51 42
6 14 CI 11 21 5.3 67 58
9 25 CI 19 29 4.4 130 84
12 34 CI 27 31 4.3 176 116
15 38 CL 30 15 6 186 180
21 55 CL 44 13 6 198 264
24 58 CL 46 11 6 204 276
0.5 11 CL 7 8 6 43 42
3 8 CL 5 9 6 46 30
6 34 CL 26 10 6 159 156
9 24 CL 18 17 6 128 108
12 39 CL 31 14 6 186 186
15 60 CL 48 18 5.8 286 278
18 59 CL 47 12 6 273 282
21 41 CL 33 9 6 186 198
0.5 6 CI 3 28 4.5 22 14
9 45 CI 32 27 4.6 183 147
12 41 CI 31 20 5.4 170 167
15 35 CI 26 23 5 147 130
18 36 CL 27 11 6 147 162
24 100 CI 100 21 5.3 329 530
27 100 CI 92 27 4.6 329 423
30 51 CI 38 29 4.4 205 167
39 100 CI 100 26 4.7 261 470
0.5 14 CL 8 15 6 52 48
3 10 CL 6 15 6 34 36
9 40 CI 29 30 4.4 166 128
12 50 CI 38 19 5.6 193 213
15 37 CI 28 25 4.8 149 134
18 42 CL 32 16 6 164 192
24 88 CH 66 31 4.3 332 284
27 87 CH 65 37 4.2 331 273
30 100 CI 75 31 4.3 349 323
33 68 CH 51 33 4.3 273 219
0.5 8 CI 5 23 5 29 25
3 15 CI 8 25 4.8 60 38
6 23 CI 16 28 4.5 84 72
9 35 CI 25 26 4.7 147 118
12 40 CI 30 22 5.2 166 156
18 43 CI 32 24 4.9 179 157
24 100 CH 75 35 4.2 325 315
27 100 CH 75 39 4.2 302 315
30 100 CI 75 19 5.6 275 420
33 100 CI 75 27 4.6 315 345
39 100 CI 75 33 4.3 359 323
6.5 32 CI 24 23 5 125 120
12.5 95 CL 75 10 6 334 450
15.5 84 CI 67 30 4.4 336 295
21.5 100 CI 100 26 4.7 352 470
30.5 100 CH 100 34 4.3 349 430
33.5 100 CI 100 32 4.3 367 430
36.5 100 CI 100 28 4.5 376 450
0.5 8 CI 5 22 5.2 30 26
3 12 CI 8 25 4.8 41 38
6 6 CL 5 10 6 20 30
15 81 CL 64 10 6 323 384
21 100 CI 100 26 4.7 308 470
24 100 CI 69 18 5.8 347 400
36 100 CI 100 25 4.8 362 480
39 100 CI 100 24 4.9 338 490
6.5 49 CI 37 29 4.4 182 163
18.5 100 CI 100 24 4.9 346 490
21.5 79 CI 63 23 5 319 315
24.5 100 CL 100 9 6 327 600
33.5 100 CI 100 31 4.3 371 430
36.5 100 CH 100 34 4.3 368 430
40 100 CI 100 18 5.8 284 580
0.5 13 CI 8 21 5.3 41 42
3 9 CI 6 25 4.8 37 29
15 97 CI 77 25 4.8 362 370
18 100 CI 100 23 5 370 500
21 100 CI 100 30 4.4 334 440
27 100 CI 100 22 5.2 339 520
33 100 CI 100 21 5.3 337 530
36 100 CI 100 25 4.8 348 480
39 100 CI 100 24 4.9 352 490
2.75 15 CI 9 30 4.4 46 40
5.75 29 CL 22 15 6 107 132
11.75 100 CI 76 24 4.9 286 372
14.75 100 CI 79 28 4.5 327 356
17.75 100 CI 79 32 4.3 354 340
20.75 100 CI 79 29 4.4 349 348
23.75 75 CI 60 26 4.7 299 282
26.75 80 CI 63 30 4.4 320 277
29.75 100 CH 79 34 4.3 331 340
32.75 100 CH 79 38 4.2 312 332
35.75 100 CH 79 37 4.2 357 332
38.75 100 CI 79 26 4.7 367 371
0.5 8 CL 5 10 6 30 30
3 13 CL 8 16 6 46 48
6 27 CI 21 24 4.9 102 103
9 30 CI 23 20 5.4 110 124
12 57 CI 45 25 4.8 211 216
18 100 CH 65 40 4.2 299 273
21 100 CH 79 36 4.2 241 332
24 65 CH 52 34 4.3 266 224
27 75 CI 60 32 4.3 298 258
30 81 CH 64 41 4.2 323 269
33 75 CH 60 42 4.2 304 252
36 87 CI 69 27 4.6 344 317
39 68 CI 54 31 4.3 283 232
0.5 27 CL 16 12 6 44 96
33.5 100 CI 79 31 4.3 237 340
36.5 100 CI 79 29 4.4 325 348
40 100 CI 79 25 4.8 311 379
0.5 5 CI 3 20 5.4 20 16
3 12 CL 7 17 6 41 42
21.5 100 CI 79 21 5.3 286 419
24.5 100 CI 75 21 5.3 309 398
36.5 100 CH 32 29 4.4 312 141
18 100 CI 50 27 4.6 321 230
21.5 100 CI 79 21 5.3 315 419
24.5 74 CH 79 24 4.9 306 387
27.5 100 CH 79 23 5 325 395
36.5 100 CI 79 23 5 341 395
39.5 100 CI 79 24 4.9 319 387
0.5 5 CL 5 16 6 18 30
3 6 CL 6 15 6 21 36
6 5 CI 5 23 5 19 25
9 13 CI 13 23 5 49 65
15 55 CI 45 30 4.4 217 198
18 40 CI 40 22 5.2 153 208
36 100 CI 100 31 4.3 329 430
0.5 5 CL 5 19 5.6 19 28
3.5 4 CI 4 23 5 15 20
6.5 14 CI 14 27 4.6 49 64
15.5 80 CI 80 24 4.9 309 392
30.5 100 CI 100 27 4.6 314 460
33.5 100 CI 100 27 4.6 330 460
36.5 100 CL 100 37 4.2 317 420
40 100 CH 100 35 4.2 344 420
0.5 21 CI 12 26 4.7 80 56
3 12 CL 7 16 6 44 42
15 100 CI 79 21 5.3 320 419
18 85 CI 67 22 5.2 337 348
21 78 CI 61 27 4.6 317 281
24 90 CI 71 24 4.9 321 348
0.5 14 CL 20 12 6 44 120
6 15 CL 7 14 6 56 42
9 26 CI 13 25 4.8 82 62
15 78 CL 79 18 5.8 277 458
18 100 CI 75 25 4.8 326 360
21 100 CI 45 28 4.5 309 203
24 100 CI 74 26 4.7 267 348
27 100 CI 65 25 4.8 281 312
39 100 CI 79 24 4.9 272 387
0.5 34 CI 8 22 5.2 95 42
3 10 CL 5 12 6 37 30
6 11 CI 10 15 6 44 60
9 18 CI 19 19 5.6 72 106
12 89 CI 35 28 4.5 343 158
15 100 CI 61 27 4.6 337 281
18 95 CI 79 21 5.3 348 419
21 57 CI 79 32 4.3 323 340
24 94 CI 79 26 4.7 314 371
27 83 CI 79 25 4.8 318 379
0.5 10 CL 6 15 6 36 36
6 11 CI 7 11 6 37 42
9 25 CI 19 28 4.5 95 86
18 100 CI 79 22 5.2 337 411
21 73 CH 57 42 4.2 241 239
24 55 CI 43 28 4.5 224 194
27 85 CI 67 28 4.5 316 302
39 100 CI 79 30 4.4 331 348
0.5 9 CL 5 10 6 22 30
3 13 CL 8 14 6 28 48
6 19 CI 14 26 4.7 65 66
9 29 CI 22 18 5.8 108 128
21 62 CL 49 16 6 58 294
6 26 CL 17 19 5.6 37 95
30 92 CI 72 26 4.7 325 338
6 45 CI 45 21 5.3 185 239
2.75 24 CL 15 9.2 6 27 90
2.75 24 CL 15 11.3 6 25 90
0.5 6 CI 4 11.4 6 29 24
3 10 CI 6 15.9 6 33 36
6 27 CL 21 9.6 6 26 126
2.75 10 CI 6 16.5 6 28 36
5.75 27 CI 21 16.8 6 36 126
0.5 17 CL 11 10.1 6 22 66
3 18 CL 11 9.1 6 24 66
2.75 15 CL 9 10.9 6 26 54
0.5 20 CL 12 8.6 6 23 72
0.5 13 CH 8 21.1 5.2 52 42
3.5 32 CI 22 19.4 5.4 37 119
0.5 15 CL 9 11.9 6 22 54
3 24 CL 14 14.3 6 33 84
0.5 17 CI 11 22.4 5 37 55
2.75 32 CL 19 11.7 6 21 114
0.5 4 CL 2 13.3 6 21 12
0.5 5 CL 3 12.6 6 24 18
5.75 26 CL 20 14.8 6 29 120
0.5 13 CL 8 16 6 21 48
0.5 15 CL 9 18 5.8 18 52

The main objective of the present invention is to assess the effect of soil parameter uncertainties on the reliability of RC bridges, through the consideration of soil–structure interaction. To achieve this goal SPT N values to estimate the shear strength properties of soils, such as cohesion (c) and angle of internal friction (ɸ), of coarse-grained and fine-grained soils. In the absence of laboratory test data, researchers/practitioners used SPT N value correlation to estimate the c and ɸ of soils for obtaining the Shear Parameters. Around 40 Boreholes of 20 bridges with alternated fine and granular soil layers considered. In this research, thorough study/evaluation has been done on usage of certain interpretations for estimation of design shear parameters for SM (SP-SM), SC, CL,CI& CH Soils based on available SPT (N) Values and laboratory (gradation and Atterberg limits) data and comparing the same with available GTI data (shear data from Lab Results) pertaining to the design of shallow and pile foundations. Thorough evaluation of the available lab data and correlations was required for arriving at the shear strength parameters for SM & SC Soil (i.e., Phi- angle of friction) and CL, CI & CH Soil (i.e., C Value) to be considered in the absence of laboratory shear test results.

It will be recognized that the above described subject matter may be embodied in other specific forms without departing from the scope or essential characteristics of the disclosure. Thus, it is understood that, the subject matter is not to be limited by the foregoing illustrative details, but it is rather to be defined by the appended claims.

While specific embodiments of the invention have been shown and described in detail to illustrate the novel and inventive features of the invention, it is understood that the invention may be embodied otherwise without departing from such principles.
, Claims:WE CLAIM

1. A method for determination of modified correlation of shear strength parameters of coarse and fine grained soils based on SPT (N1)60, for Gujarat soils
characterized in that
the correlated Phi value (N1)60 values equal to or more than 100 are very high and need to be limited to a certain maximum value.

2. The method as claimed in claim 1, wherein the correlation is used for all granular soil types SM & SC and fine grained soil types (CL, CI & CH) with majorly fine sand.

3. The method as claimed in claim 1, wherein the phi value of SM & SC soils is influenced by percentage of particles of sand, and gravel present, as well as in-situ density and (N1)60.

4. The method as claimed in claim 1, wherein the error in prediction of angle of shearing resistance of soil (Phi) for coarse grained soils adopted from correlations based on relative density used for Bridge foundation design.

Dated this the 14 th day of March 2023.

Anugu Vijaya Bhaskar Reddy, IN/PA-2420