Application seismic refraction method to characterize the building site of Injibara University building site,injibara Ethiopia

Geophysical investigation using seismic refraction method was conducted for engineering characterization of the foundation conditions of Injibara University buildings construction site located in Injibara town of Amhara Regional State, northwestern Ethiopia. The principal objective of the research was studying the suitability of the foundation earth materials underlying the site, where Injibara University is established. The seven refraction seismic spreads, seismic velocity models interpretation have provided valuable geotechnical information incorporated with available geologic information in the study area. Interpretation of geophysical data revealed that the subsurface geology of the area is composed of three layers. The topsoil consisted of clay, silt and sand mixtures having a 1-4 m thickness and 255-510 m/s p-wave velocity ranges are mapped over the whole area. The second layer attributed to the highly weathered and fractured vesicular basalt is characterized by 948-1802 m/s P-wave velocity range and revealed somewhat undulating morphology. The depth extent of this layer varies from about 10m on the North West end and southeastern parts and to about 27m around the central part. The third layer occurred in the depth range of 10-27m is characterized by greater than 2550m/s average high p-wave velocity and it is due to moderately weathered and fractured basaltic bedrock, which is deeper near to the center of the profiles and gets shallower towards North West end and southeastern portions. Besides, analyses of collected data have suggested the possible locations of minor structural discontinuities (maybe local fractures).The geophysical results show that the bedrock is found at shallow depth in the northwestern end and southeastern part of the study area, whereas in the central part of the survey area the bedrock is found relatively at high depth. Therefore, setting the building foundation is more recommended in the southeastern part of the construction site.

Applications of Geophysical Methods in Tunnel and Oil Exploration

Geophysical studies can be utilized adequately to decide the land, hydro geographical and geotechnical properties of the ground mass in which the designing development is occurring. The investigation must be given to the contractor to ensure the information related to soil or to predict the type of equipment to be used and to estimate productivity and cost. This article examined how integrated geophysical methods were carried out for the determination of the degree of fracturing and rigidity of rock mass. Data were collected from different case studies in which comparison is there between different types of methods suited for different type of evaluations. In this paper, methods involved for the explorations are seismic refraction method, electrical resistivity method, magnetic and gravity method for oil explorations. The authors found that gravity and magnetic are best suited methods for the oil sand exploration and because of the high acceptance of designing a lot latest applications expected in future. The techniques used in these methods are relatively cheap and fast finding in comparison to other methods.

Aplikasi Metode Seismik Refraksi dalam Menentukan Lapisan dan Tingkat Kekerasan Batuan di Bawah Permukaan Desa Medana Lombok Utara

The seismic refraction method is one of the geophysical methods which is based on measuring the response of seismic waves in the soil that are fractured along the soil and rock layers. One of the seismic refraction method application is to determine the layers and rocks types below the surface. This study uses a geophone as a catcher for seismic waves that are emitted below the surface. The waves caught on the geophone are converted into seismic data which can be read in a seismograph. Seismic data read by seismographs are already in digital form and stored in the central unit PASI 16S24-P. The results of the data analysis concluded that below the land surface of the village of Medana, there were 3 rock layers with a thickness of the first layer 3-4 meters, the second layer 2-5 meters and the third layer 10-17 meters. The first and second layers are still in the form of soil (less compact), while the third layer is in the form of rock (compact). The level of hardness (density) will be more compact in linear to the depth, the more the depth will be the more compact the rock. The depth in the form of hard rock starts from 16 meters to 23 meters from the ground level of the village of Medana, Central Lombok.

Advantages and Limitations of Seismic Refraction Method Using Hammer Sources

The seismic refraction surveying method uses seismic energy that returns to the surface after traveling through the ground along refracted ray paths. The first arrival of seismic energy at a detector offset from a seismic source always represents either a direct ray or a refracted ray. This fact allows simple refraction surveys to be performed in which attention is concentrated solely on the first arrival (or onset) of seismic energy, and timedistance plots of these first arrivals are interpreted to derive information on the depth to refracting interfaces. this simple approach does not always yield a full or accurate picture of the subsurface. In such circumstances more complex interpretations may be applied. The method is normally used to locate refracting interfaces (refractors) separating layers of different seismic velocity, but the method is also applicable in cases where velocity varies smoothly as a function of depth or laterally.Despite the numerous limitation of hammer seismic refraction survey, the technique is still very much in use due to the various aspects in which it is found advantageous. The most pronounce advantage of the refraction method is that it gives directly the velocities of the refracting beds. Which are needed in the depth interpretation. This this work reveals that even though there are several problem of this technique, there are also a lot of advantages, one of which is that it is the most readily available seismic energy source we can lay hands on.Hammer source is a low energy source whose use is restricted to shallow survey. Due to weak energy generated,only the first few layers of the ground subsurface can be detected. It provides only the picture of the bedrock configuration. When there arises problems such as noise, irregularities in the shallow bedrock surface or eroded and weathered rock surface, anisotropic surface, existence of blind zone, velocity reversal with depth, and when the boundary between the interfaces are non-parallel, then correction measures are necessary to improve on the results obtained. Ambiguities do occur in this technique hence it requires thought, care, a high degree of skill and a good sense of judgment.These shortcomings are not enough to dismiss the use of the hammer source in seismic refraction method as its results has been shown to be useful in solving civil engineering and hydrogeological problems. The method is economical in cost, time and area of coverage. It poses no danger to the environment to which the work is done, or neither personnel nor damage to instruments used. This work has not only enumerated the limitations and advantages of seismic refraction method using hammer source but has also made suggestions to aid in the basic problem of the method, like dipping layers, blind zone, velocity inversion occurrence and noise control.

SEISMIC REFRACTION METHOD IN THE DETERMINATION OF SITE CHARACTERISTICS

Preliminary site properties need geophysical methods to determine it, the same as the large use of the seismic refraction method to detect the layers of soil and the depth reaching the bedrock. This study was conducted to find out the subsurface profile characteristics of a backyard field in UTM, Skudai following the principles of this method. The analysis of seismic data processed using ZondST2D software by determining the first arrival time until we get a block model of 2D shape based on the primary propagation of seismic velocity wave’s in soil layers. It was found that the investigated subsurface profile consists of four layers showing the level of weathering grade ranges from 600–4000 m/s based on the classification of rock mass in Malaysia. It was found that weathering rates decreased at higher depth, with the increase of density for the material and dampness reduction of seismic velocity. It was concluded that the survey of seismic refraction in development can be used only for shallow subsurface profiles and far from noise and disturbance.

ASSESSING THE SUSCEPTIBILITY OF STRUCTURAL COLLAPSE USING SEISMIC REFRACTION METHOD

Seismic refractive survey is a very important geophysical technique used to investigate the characteristics of the subsurface. The rate of building collapse has demanded the acquaintance about the structure of the subsurface especially in area where lands are recovered from water bodies for the aim of building. This paper presents the technique used in determining the thickness of the overburden for quarry prospecting using a geophysical method called as seismic refraction method. Seismic refraction method was used to delineated two distinct layers with the first layer having a weak and incompetent parameter values. The result revealed that the first layer is composed of unconsolidated formation of soft geomaterials and peaty clay that depict the lower values of parameters. This layer is underlain directly by clay, wet sand and sandy clay of soft and weak incompetent consistencies to a depth of 7 m in the subsurface. The second layer was found to have higher parameters than the first layer. The second layer revealed that the geologic formation composed of dry sand and sandy clay of fair to good competent. The geologic formation in the second layer was found to be more competent than the first layer with high allowable capacity and low ultimate failure potential. Geologically, the composition of the first layer is more recent in age of deposition than the second layer, characterized by unconsolidated geologic formation.

Identifikasi Ketebalan Lapisan Lapuk pada Area Rawan Longsor Menggunakan Metode Seismik Refraksi (Studi Kasus: Desa Kalirejo Kabupaten Kulonprogo)

Kalirejo Village, Pengasih District, Kulonprogo Regency, is an area that is prone to landslides. The purpose of this study is to identify the weathering layer thickness, which is one of the triggering factors for landslides. This study was conducted using the seismic refraction method by applying two lines. Line 1 uses 24 geophones, has a distance of 1 meter between geophones, while Line 2 uses 24 geophones, has a distance of 2 meters between geophones. The results showed that the velocity of seismic wave propagation in the weathering layer for Line 1 was 400 m/s, and in the slip surface was 2,300 m/s. The weathering layer thickness on Line 1 is 7.6 - 9.8 meters and the slope is steep so that this location is predicted to have a potential landslide. While the velocity of seismic wave propagation in the weathering layer for Line 2 was 300 m/s, and in the slip surface was 2,200 m/s. The weathering layer thickness on Line 2 is at less than 2 meters, so this location is predicted not to have a landslide potential even though the slope is steep