Standard Penetration Test N-values Research Articles

BEARING CAPACITY ANALYSIS OF SUBSOILS, FOR SHALLOW AND DEEP FOUNDATION IN UYO TOWN, EASTERN NIGER DELTA, NIGERIA.

The Geotechnical properties of soils in Uyo town were analysed to determine the bearing capacity and develop maps for shallow and deep foundation designs, which may serve as field models, for the planning of site investigation programmes for foundation purposes. Eleven boreholes were drilled to a maximum depth of 20 meters each across Uyo town. Standard penetration tests and cone penetration tests were also carried out on the field. Soil samples were retrieved during the field investigation for various laboratory tests including liquid limits, plastic limit, bulk density, shear strength and particle size distribution. The general soil profile consists of silty clays, sandy clays and sand from top to bottom. The silty clays are firm, low compressibility clays with liquid limit and plastic limit percentages between 32%-45% and 10%-45% respectively, cohesion averages of 4˚ to 12˚ and angles of internal friction between 48KN/m2-68KN/m2. Ultimate bearing capacities of this horizon range from 354.6kN/m2 to 866.7kN/m2.The sandy clays are also firm, low to intermediate plasticity clays with liquid limit and plasticity indexes of 29% - 42% and 9%-15% respectively. Their cohesion averages range between 50KN/m2-65KN/m2 and angles of internal friction between 6˚-12˚. The ultimate bearing capacities of this clay range from 482.5KN/m2 to 906.2KN/m2. The sand is a poorly graded, medium dense sand with standard penetration test N-values between 8 to 23. Pile bearing capacities of the sand gave ultimate and allowable bearing capacities between 10262.9KN-11510.2KN and 4105.2KN-4604.1KN respectively. The sand substratum is a suitable termination depth for piles.

Assessment of Ground Movement at Cigombong Bridge by Using Finite Element Analysis: A Case Study in West Java, Indonesia

Ground movement phenomena were detected at abutment A2 of Cigombong Bridge, causing the abutment to hit a girder. A thorough investigation has been performed by inspecting the structure condition and nearby landslide occurrences directly on site. Additional borings with Standard Penetration Test (SPT) were also conducted to evaluate the actual soil condition in the abutment area. Moreover, monitoring of subsurface movement was performed regularly with inclinometers. Such additional borings and inclinometers were located at the road elevation beside the wing wall and the existing ground surface near the abutment footing. During the installation of inclinometer pipes, soil identification and SPT were conducted. Consequently, the soil condition and SPT N-value profiles can be obtained. It was established that the original soil condition is very soft clay with an SPT N-value of 1 to 4 blows/30 cm. Furthermore, the inclinometer monitoring results showed that lateral displacements were identified in both inclinometers. Based on these findings, a 3D finite element analysis was then performed to investigate the effects of ground movement on the abutment and the foundations. The results showed a possibility of pile crack and overstressed pile due to the ground movement induced by compression of soft soil.

Investigation of Soft Layer in between Hard Layer for Sedimentary Rock Formation by using Electrical Resistivity Analysis

This study aims to predict the occurrences of soft layers in between hard layers in sedimentary rock formation based on electrical resistivity analysis. ABEM Terrameter LS Box with 40 electrodes with 2.5 meters spacing in pole-dipole method was used. Standard Penetration Test (SPT) was conducted to obtain the value for the number of blows (N-value). RES2DINV was used to analyse a two-dimensional illustration of the soil layers in the pseudo section diagram. Results show that the groundwater table is located 2.0 meters below the ground surface. Based on the resistivity analysis, the subsurface profile is consists of topsoil, soft silty clay (N0-N4, 6 > Ω > 20 ohm), medium-stiff silty clay (N5-N6, 20>Ω>360 ohm), medium dense coarse sands (N13-N16, 361>Ω>550 ohm), stiff silty clay (N10-N18, 550>Ω>720 ohm), hard silty clay and gravel (N50, 720>Ω>1100 ohm), and moderate weathered and slightly fractured shale stone (N50, Ω>1100 ohm). Although the correlation between resistivity values and SPT N-values shows a very good relationship with R2 ranges from 0.83 to 0.89, electrical resistivity analysis is not suitable to determine the soft layer in between hard layer in a sedimentary rock formation due to the presence of high ground water table.

Comprehension of Conventional Methods for Ultimate Bearing Capacity of Shallow Foundation by PLT and SPT in Southern Bhutan

Shallow foundations are very distinctive in Bhutan since construction of buildings are regulated to 7-8 story and the superstructure loads are not very high compared to high-rise buildings elsewhere. However, the safety of the buildings depends primarily on the stability of the subsoil. This can be evaluated by estimating Ultimate Bearing Capacity (UBC) and it is the measure of the subsoil strength. In the current study, field test such as Plate Load Test (PLT) and Standard Penetration Test (SPT) are conducted in the study area which are most common conventional methods adopted in Bhutan given the typology of infrastructures. Detail analysis is performed for PLT and SPT data collected from southern parts of Bhutan to assess the shear stability characteristics of the subsoil. The field exploration was carried out at embedment depth of 1.5 m in both the tests. PLT directly provides UBC through load and settlement plot. With SPT N-values, UBC are estimated for square footing using empirical correlations proposed by Terzaghi 1943 and Meyerhof 1963. The results are compared to comprehend the design parameters. Both in-situ test resulted close estimation of UBC. In SPT, analysis results indicate Meyerhof's correlation more conservative suggesting safe and economical foundation design. The parametric analysis was performed to deduce and validate correlations among the parameters used. The subsoil lithology was reviewed to validate the subsoil characteristics for the southern belt of Bhutan to which resistivity profiles of the underlying strata of the subsoil in the region have been reported similar to the investigation conducted in this study.

Geotechnical Investigation for Estimation of Liquefaction Hazard for the Capital City of Gujarat State, Western India

Gandhinagar, the capital city of Gujarat state (Western India), is situated in the middle of the moderately active Cambay rift. The region lies under the seismic zone III of the seismic zoning map of India. The city rests on 250–300 m thick flood plain deposits consisting of coarse sand, silt and clay. In this work, liquefaction hazard is assessed using geotechnical investigations. A total of 14 boreholes of 35 to 50 m depth were drilled with sampling at every 1.5 m depth interval (till termination depth) covering entire Gandhinagar city. A standard penetration test (SPT N-value) was conducted at an interval of 3 m depth in every borehole. We used 400 samples for the estimation of index properties of the soil in the study area. The lithological distribution in the city is also mapped based on the soil classification. The liquefaction hazard is estimated by standard methodologies using density, plasticity index, groundwater level, Peak Ground Acceleration (PGA), fine content and Standard penetration test (SPT) N value. The site-specific PGA values at the surface are estimated by carrying out ground response analysis. The study shows that the area comprises of alternate layers of argillaceous and arenaceous soil. We found that in general the area has low liquefaction potential but in case of heavy rainfall the chances of liquefaction may increase as the soils are conducive of liquefaction.

Coupling of SPT and 3D full waveform inversion for deep site characterization

Detailed information of soil/rock variability and properties for the entire volume of supporting materials is crucial for the successful design and construction of deep foundations. Traditional invasive testing methods such as the standard penetration test (SPT) and the cone penetrometer test (CPT) only sample a small volume of soil/rock properties near the device's tip. Surface-based seismic methods can provide overall subsurface conditions but are limited to shallow depths due to the dominancy of surface waves. To address this issue, we present a novel SPT-seismic testing method for deep site characterization. Seismic wavefields generated by SPT blows at various depths are recorded by a 2D grid of geophones on the ground surface, and analyzed by a 3D full-waveform inversion (3D FWI) to extract subsurface material properties. Unlike surface-based wavefields dominated by surface waves propagating near the ground surface, the SPT-seismic wavefields are rich in body waves propagating from great depths that allow extracting detailed material properties at depths. The method is tested on in-depth source synthetic data and SPT-source field data. The results of the synthetic experiment indicate that the method successfully images soil layering with a buried anomaly. Field experiment results provide new insights into its utility as a viable geophysical tool for deep site characterization. 3D subsurface S-wave and P-wave velocities within 9 m around the SPT boring are well characterized, including two deep voids at 14–18 m depth. Comparison with the surface-based 3D FWI method proves the superiority of the presented method in imaging deep structures. S-wave velocity values of the final inverted result are also compared with SPT N-values and a good overall agreement over the whole depth is observed.

3D viscoelastic full waveform inversion of seismic waves for geotechnical site investigation

Full waveform inversion (FWI) methods are becoming efficient geophysical tools for geotechnical site investigation. They rely on a mathematical description of wave propagation phenomena to generate synthetic wave-fields, which are then matched with measured wave-fields for extraction of material properties. Due to the inherent computational challenges in implementing a viscoelastic treatment of the wave propagation phenomena, most of the existing 3D FWI algorithms are based on an elastic treatment, and hence ignore the anelastic behavior of materials. The focus of this study is to account for the anelastic effect of materials in the inversion analysis to improve inverted results. Therefore, a 3D viscoelastic FWI method is developed and tested on synthetic and field datasets. The method is based on an existing solution of 3D viscoelastic wave equations (finite-difference solver SOFI3D) and the adjoint-state inversion approach. The results show that the viscoelastic waveform analysis was able to characterize low- and high-velocity synthetic layers, and real variable soil layers. The S-wave velocity (Vs) profiles from field experiment generally agree with invasive standard penetration test (SPT) N-values, including identification of a low-velocity zone. Vs profiles obtained from a 3D elastic FWI are also included for comparison, and results from the viscoelastic inversion are more consistent with the SPT N-values in both trend and magnitudes.

GEOTECHNICAL PROPERTIES AND STRENGTH CHARACTERIZATION OF NIGERIAN SOILS

Strength characteristics of foundation soils in the six geo-political zones of Nigeria were evaluated based on standard penetration test (SPT) results using some conventional empirical/analytical models and the bearing capacity was predicted by numerical analysis using Plaxis 3D, a finite element application package. The SPT N-values were first corrected to the standard average energy of 60% (N60) before they were used to correlate soil properties. Evaluation of the soil properties were done at foundation embedment depths of 0.6, 2.1, 3.6, 5.1, 6.6, 8.1, 9.6, 11.1 and 12.6 m. The results of overconsolidation ratio, rigidity index, relative density, angle of internal resistance, undrained shear strength and unconfined compressive strength show that the strength characteristics of Nigerian soils is lowest on the average in the South South (SS) geo-political zone, followed by South West (SW), South East (SE), North East (NE), North West (NW) and the North Central (NC) geo-political zone has the highest prediction of strength characteristics. Bearing capacity generally increased with boring depth and having its lowest values in the SS geo-political zone and increased for the remaining zones in the order of SW, SE, NE, NW and the NC geopolitical zone.

Foundation evaluation of underground metro rail station using geophysical and geotechnical investigations

Excavations for underground space developments in a thickly populated urban area are sometimes hindered by unexpected formidable consequences like formation of sinkholes or uneven settlement of foundations. Such troublesome incidences occasionally damage structures in the vicinity of excavations. Although adequate design guidelines and codes of practices are adopted, the disturbance of subsurface regime due to excavation or construction activities often leads to undesired stability issues with resultant appearance of weak zones. The reinforcement of weak zones by grouting is one of the common remedies, without demarcating the weak or the affected zones becomes counter-productive. Excavation at a location in Chennai mega-city for metro rail was severely affected by soil piping with development of sinkholes and weakening of the surrounding strata. Subsequently development of cracks in the adjacent buildings, and caused tilting of the nearby taller structures. The mandated the geophysical and geotechnical investigations were carried out to demarcate the affected area to avoid further deterioration of the site. Cross-hole seismic P- and S-wave velocities were estimated between10-pairs of boreholes up to 20 m depth on both the sides of the excavation. Two electrical resistivity tomography (ERT) profiles (each of 141 m in length) were carried out in the same location. Cross-hole S-wave velocity profiles and resistivity tomograms clearly indicate the presence of weak zones, and possible sinkhole locations. Site specific empirical relationship was established between S-wave velocity and standard penetration test (SPT) N-value. This relationship was further used for determination of SPT N-values from the measured VS values to compare the subsurface conditions identified under pre- and post-excavations. The results confirmed the presence of weak zones, which are responsible for the weakening of the surrounding strata in the foundation. Geophysical and geotechnical investigations, similar to present investigation, can be useful for designing metro rail projects in a subsurface environment comprising alluvium, sand, clay mixed with silt, pebbles and boulders, lying near a region of ground water pocket in a thickly populated urban area.

Pre-shaking effects on volumetric strain and cyclic strength of sand and comparison to unsaturated soils

Repeated small shaking events due to earthquakes significantly enhance liquefaction resistance of soils. Analyses of liquefaction case histories show that aged soils in seismically active zones tend to be less vulnerable to liquefaction despite having similar index parameters—such as standard penetration test N-values and shear wave velocities—as young soils. Significant efforts have been devoted to better understand the effects of the cyclic pre-shearing on liquefaction resistance and it was found that this effect depends on the number of cycles and cyclic stress ratio. However, none of these parameters quantify the improvement of liquefaction resistance due to pre-shaking. This study investigates the pre-shearing effects on liquefaction resistance through laboratory tests and centrifuge tests. An attempt was made to explain the effects quantitatively with a single index parameter of the volumetric strain caused by pre-shearing. It was confirmed from triaxial tests that the liquefaction resistance of pre-sheared sand uniquely increased with increasing volumetric strain regardless of the cyclic shear stress ratio and the number of cycles during the pre-shearing. To examine the pre-shaking effects on the liquefaction strength of sand under a level ground condition, centrifuge tests were conducted in this study. Sand models were subjected to small shaking events repeatedly, which were weak enough not to cause liquefaction. It was observed that changes in the index parameters of the models, including soil density (volumetric strain), shear wave velocity, and horizontal earth pressure during the pre-shaking events were very small. At the end of the test, the sand was subjected to a strong shaking event because models that had gone through pre-shaking need larger shaking acceleration to liquefy. Liquefaction resistance was derived from acceleration records with the aid of the cumulative damage theory. The relationship between liquefaction resistance ratio and volumetric strain that occurred in the pre-shaking events coincides with the relationship obtained from the triaxial tests. After the extensive liquefaction event, all index parameters except soil density—K0, Vs, liquefaction resistance—tended to return to their original values (before the pre-shaking).

Prediction of standard penetration test N-value from dynamic probing light N-value using ANFIS and multiple regression models

ABSTRACT Standard penetration test (SPT) is one of the most widely used tools to predict the soil properties. In recent years, the dynamic probing light (DPL) test has been performed more frequently for geotechnical applications because it is more cost-effective and fast. Since the majority of empirical equations of soil properties are related to SPT N-value, it is beneficial to find the best correlation between SPT and DPL N-values. In this study, the adaptive neuro-fuzzy inference system (ANFIS) and multiple regression (MR) are used to predict the correlation between SPT and DPL N-values. To achieve this goal, the soil properties of 64 sample specimens of silty clay were calculated at various depths. Three parameters including depth, total density, and DPL N-value were chosen as the input of the models. Results show that both methods estimate the correlation between SPT and DPL N-values precisely. However, ANFIS predicts more accurately than multiple regression.

Estimating in situ dynamic strength and deformation properties of Niigata East Port sand deposits

The dynamic strength and deformation properties of Niigata East Port sand deposits were examined based on cyclic triaxial tests on samples obtained from two-chamber hydraulic piston samplers with inner diameters of 50 mm and on samples obtained using the frozen sampling method. An economically feasible method of estimating the in situ void ratio, the relative density Dr, the cyclic stress ratio RL20 under 20 uniform stress cycles, and the initial modulus of rigidity GCTX as obtained from cyclic triaxial testing was also developed, and its applicability to samples of sand deposits obtained from Niigata’s East Port, the 3rd Meiji fortress in Tokyo Bay, a port in the Kansai area of Western Japan, Niigata Meike, and Niigata Airport was also assessed. The measured RL20 values ranged from 0.1 to 0.33 and were independent of both Dr and the normalized standard penetration test N-values. The ratios of GCTX to the initial in situ modulus of rigidity calculated using P/S logging during tube sampling ranged from 0.43 to 0.71 and were similar to those obtained by the frozen sampling method. The change in the dynamic strength and deformation properties caused by tube sampling can be adjusted appropriately to reflect the in situ conditions by using the economically feasible method. When combined with the economically feasible method, the tube sampling method can provide a simpler and more economical method of sand sampling than can be achieved using the frozen sampling method.

STRENGTH CHARACTERIZATION OF FOUNDATION SOILS AT FEDERAL UNIVERSITY LOKOJA BASED ON STANDARD PENETRATION TESTS DATA

Strength characteristics of foundation soils in the Permanent site of the Federal University Lokoja in Kogi State were evaluated based on standard penetration test (SPT) results using some conventional analytical models proposed by different researchers. The study was carried out in order to take precise engineering decisions on the type of foundations suitable for the proposed structures and to determine the optimal depth of foundation embedment. The SPT N-values were first corrected to the standard average energy of 60% (N60) before they were used to correlate soil properties. Evaluation of the soil properties were done at foundation embedment depths of 0.6, 2.1 and 3.6 m. Results show that bearing capacity generally increased with boring depth. Based on the Meyerhof allowable bearing pressure estimation method, foundation pressures in the range of 150 – 600 kN/m 2 were evaluated for use in the study area at shallow depths (depths in the range of 0.6 - 3.6 m). http://dx.doi.org/10.4314/njt.v36i3.2

INVESTIGATION OF SHALLOW FOUNDATION SOIL BEARING CAPACITY AND SETTLEMENT CHARACTERISTICS OF MINNA CITY CENTRE DEVELOPMENT SITE USING PLAXIS 2D SOFTWARE AND EMPIRICAL FORMULATIONS

This study investigated the soil bearing capacity and foundation settlement characteristics of Minna City Centre development site using standard penetration test (SPT) data obtained from10 SPT boreholes at 0.6, 2.1 and 3.6 m depths to correlate soil properties. Evaluation of foundation bearing capacity and settlement characteristics for geotechnical preliminary design of foundations was carried out using some conventional empirical/analytical models and numerical modelling. The aim was to investigate and determine the geotechnical parameters required for adequate design of Physical structures of the proposed Minna City Centre, at Minna the capital of Niger state. The SPT N-values were corrected to the standard average energy of 60% (N60) before the soil properties were evaluated. Using the corrected N-values, allowable bearing pressure and elastic settlement of shallow foundations were predicted at 50 kN/m 2 applied foundation pressure. The numerical analysis results using Plaxis 2D, a finite element code, shows the analytical/empirical methods of estimating the allowable bearing pressure and settlements of shallow foundations that provided acceptable results. Results obtained show that an average bearing capacity value of 100 – 250 kN/m 2 can be used for shallow foundations with embedment of 0.6 to 3.6 m on the site.  http://dx.doi.org/10.4314/njt.v36i3.1

STRENGTH CHARACTERIZATION OF FOUNDATION SOILS AT FEDERAL UNIVERSITY LOKOJA BASED ON STANDARD PENETRATION TESTS DATA

Strength characteristics of foundation soils in the Permanent site of the Federal University Lokoja in Kogi State were evaluated based on standard penetration test (SPT) results using some conventional analytical models proposed by different researchers. The study was carried out in order to take precise engineering decisions on the type of foundations suitable for the proposed structures and to determine the optimal depth of foundation embedment. The SPT N-values were first corrected to the standard average energy of 60% (N60) before they were used to correlate soil properties. Evaluation of the soil properties were done at foundation embedment depths of 0.6, 2.1 and 3.6 m. Results show that bearing capacity generally increased with boring depth. Based on the Meyerhof allowable bearing pressure estimation method, foundation pressures in the range of 150 – 600 kN/m2 were evaluated for use in the study area at shallow depths (depths in the range of 0.6 - 3.6 m).http://dx.doi.org/10.4314/njt.v36i3.2

INVESTIGATION OF SHALLOW FOUNDATION SOIL BEARING CAPACITY AND SETTLEMENT CHARACTERISTICS OF MINNA CITY CENTRE DEVELOPMENT SITE USING PLAXIS 2D SOFTWARE AND EMPIRICAL FORMULATIONS

This study investigated the soil bearing capacity and foundation settlement characteristics of Minna City Centre development site using standard penetration test (SPT) data obtained from10 SPT boreholes at 0.6, 2.1 and 3.6 m depths to correlate soil properties. Evaluation of foundation bearing capacity and settlement characteristics for geotechnical preliminary design of foundations was carried out using some conventional empirical/analytical models and numerical modelling. The aim was to investigate and determine the geotechnical parameters required for adequate design of Physical structures of the proposed Minna City Centre, at Minna the capital of Niger state. The SPT N-values were corrected to the standard average energy of 60% (N60) before the soil properties were evaluated. Using the corrected N-values, allowable bearing pressure and elastic settlement of shallow foundations were predicted at 50 kN/m2 applied foundation pressure. The numerical analysis results using Plaxis 2D, a finite element code, shows the analytical/empirical methods of estimating the allowable bearing pressure and settlements of shallow foundations that provided acceptable results. Results obtained show that an average bearing capacity value of 100 – 250 kN/m2 can be used for shallow foundations with embedment of 0.6 to 3.6 m on the site.  http://dx.doi.org/10.4314/njt.v36i3.1

Surface soil assessment in the Ubhur area, north of Jeddah, western Saudi Arabia, using a multichannel analysis of surface waves method

Ten boreholes drilled in Ubhur area up to the depth of bedrock indicted the shallow depth of bedrock where the average depth ranges between 10 and 15 m. The standard penetration test N-values of these boreholes were measured and averaged. Based on N-values to the depth of bedrock, Ubhur area can be classified as site class C and D. Multichannel analysis of surface waves technique has been applied along seventy six profiles using 24-channel geophone array and 4.5Hz vertical geophones with 1m geophone spacing and sledgehammer and/or weight drop as seismic energy sources. Values of shear wave velocity to 30 m are calculated and then averaged (Vs30) where it ranges between 310.08 m/s and 1139.8 m/s. Therefore, Ubhur area can be classified into site class B, C and D based on site classification of the national earthquake hazards reduction program (NEHRP) recommendations. Accordingly, the greatest part of the study area falls in site class C while class B and D covered limited areas in the western and the eastern parts respectively. Depending on the shallow depth of bedrock in the study area, the Vs30 parameter is not applicable in the study area so the average values of Vs for the soil thickness, excluding the bedrock, have been calculated and mapped for site class C and D only. So Vs30 approach is not applicable for areas with shallow depth of bedrock which gives higher classification.

Index Properties of Coastal Plain Soils of Southeastern Virginia

Abstract The Coastal Plain soils of Virginia generally comprise recent marine and fluvial deposits. It is widely accepted that grain size, plasticity, and water content of the soil are indices that can be used to geotechnically characterize fine-grained soils. The objective of this study was to determine whether the soils from a specific geologic formation have consistent or similar index properties. The data from a previously performed extensive field exploration in the Coastal Plain soils of Virginia were used in the study. The data were divided by local geology and subdivided into separate groups based on the soil fines content (FC) and density. Mean values for water content, Standard Penetration Test N-Value, Atterberg limits, FC, and pocket penetrometer tests were then determined for each geology. The statistical analysis of soil index properties was performed for soils in different formations. The results allow better identification of soils in different formations from index property testing.

Predicting standard penetration test N-value from cone penetration test data using artificial neural networks

Standard Penetration Test (SPT) and Cone Penetration Test (CPT) are the most frequently used field tests to estimate soil parameters for geotechnical analysis and design. Numerous soil parameters are related to the SPT N-value. In contrast, CPT is becoming more popular for site investigation and geotechnical design. Correlation of CPT data with SPT N-value is very beneficial since most of the field parameters are related to SPT N-values. A back-propagation artificial neural network (ANN) model was developed to predict the N60-value from CPT data. Data used in this study consisted of 109 CPT-SPT pairs for sand, sandy silt, and silty sand soils. The ANN model input variables are: CPT tip resistance (qc), effective vertical stress (σv′), and CPT sleeve friction (fs). A different set of SPT-CPT data was used to check the reliability of the developed ANN model. It was shown that ANN model either under-predicted the N60-value by 7–16% or over-predicted it by 7–20%. It is concluded that back-propagation neural networks is a good tool to predict N60-value from CPT data with acceptable accuracy.

Predictive Relationship for Estimation of Vs30 Using Shallow Bore Logs for Karachi

Standard Penetration Test (SPT) is one of the most widely adopted methods for determination of the average shear wave velocity for the top 30 m of soil at a given site, Vs30. However, in many cases, the bore logs do not extend to the required depth of 30 m. In such scenarios, Vs30 needs to be predicted using the average shear velocity of shallow bore logs (depth <30 m), Vsd. This paper investigates the relationship between the average shear wave velocity for a shallow bore log and the average shear wave velocity for the top 30 m of soil at a given site for Karachi. To this end, a large dataset of bore logs is congregated which includes 140 deep bore logs with the depth extending up to or exceeding 30 m and 1,350 shallow bore logs with the depth below 30 m. The most suitable relationship is selected from the literature for conversion of the SPT N-values to corresponding shear wave velocity. Utilizing the deep bore logs, a predictive relationship is developed herein to correlate the average shear wave velocity for the shallow bore log with Vs30. A comparative analysis of the relationship developed in this paper is carried out with two existing methods, namely the extrapolation assuming constant velocity and extrapolation using the regression coefficients proposed for California. Based on the statistical study, it is noted that the extrapolation assuming constant velocity and extrapolation using regression coefficients proposed in this work produce better estimates of Vs30. Finally, Vs30 maps are generated for Karachi.