CN114329953A - Method for judging whether screw pile enters bearing stratum or not - Google Patents

Abstract

The invention provides a method for judging whether a screw pile enters a bearing stratum or not, which comprises the steps of installing a torque sensor at the joint of a power head of a spiral drilling machine and a screw, monitoring the torque received by the screw in the drilling process in real time to obtain a relation curve of the torque and the depth, and judging whether the pile tip reaches the bearing stratum or not in the drilling process of the screw pile according to the change characteristics of the relation curve. The method can accurately and intuitively judge whether the pile end reaches the bearing layer or not in time during the construction process of the screw pile, thereby ensuring the foundation reinforcement treatment quality, accelerating the construction progress, effectively controlling the length of the pile while ensuring the bearing capacity of the screw pile and reducing the cost.

Description

A method for determining whether a screw pile enters the bearing layer

technical field

The invention belongs to the field of civil and transportation foundation treatment, and in particular relates to a method for judging whether a screw pile reaches a bearing layer during foundation treatment.

Background technique

In road engineering construction, screw piles and original soil are used to form a composite foundation to achieve the purpose of foundation reinforcement. Due to the long construction route and large construction area, there are more requirements for the number of piles. At the same time, due to the complexity and uneven distribution of the stratum geological structure, it is very difficult to calculate the specific length of each pile according to the single-pile bearing capacity design method, and it requires a lot of manpower and time. However, in the process of screw pile construction, if the pile end reaches a good bearing layer and enters a certain embedding depth as required, it can not only increase the ultimate bearing capacity of the single pile, effectively control the settlement, but also ensure the overall stability of the roadbed. On the other hand, if the length of the pile is too short and the end of the pile does not reach the bearing layer selected in the design, the actual bearing capacity of the subgrade will be greatly reduced, resulting in abnormal settlement or even cracking of the subgrade. If the length of the pile is too long and the depth into the bearing layer is too large, the material consumption of the pile body will be increased invisibly and the engineering cost will be increased. Therefore, it is very necessary to accurately judge whether the pile end has reached the bearing layer selected by the design during the construction of the screw pile.

At present, most of the methods for judging whether the pile end of the screw pile reaches the bearing layer during the construction process remain at the level of experience. The main judgment methods are:

1) Estimate the position of the bearing layer by using the strata reported in the geological prospecting report;

2) Make an empirical judgment on whether the drilled cuttings or slag have reached the bearing rock formation;

3) The depth of the bearing layer of the pile is determined based on the depth of the bearing layer of the adjacent boreholes;

4) Determine whether the bearing layer is reached according to the degree of vibration of the drilling rig (difficulty of drilling);

5) Looking at the ammeter, it is very important for the ammeter to move, which means that the drilling can not go on, and it has reached the holding layer.

However, these judgment methods all have certain defects:

1) Geological survey cannot be done one by one. The undulating rock formations and complex weathering conditions cannot be accurately described in the geological survey report;

2) There are often boulders in the rock formation, and the drilled boulder blocks are similar to the rock of the bearing layer, which is prone to misjudgment and accidents;

3) The strike of the stratum generally has a dip angle, and the variability of the dip angle leads to different depths of the bearing layers of adjacent pile holes;

4) The severity of vibration of the drilling rig and the degree of movement of the ammeter value are judged by the operator of the drilling rig based on experience, which is highly subjective.

Therefore, the methods of judging whether the pile end has reached the bearing layer in current engineering practice are all inaccurate.

Invention patent CN201510878558 provides a method for detecting the bearing layer at the bottom of a mechanically perforated concrete cast-in-situ pile, which includes the following steps: ① uniformly placing several dual detectors along the circumferential direction at the bottom of the large-diameter pile hole; ② using an electric spark source to The elastic wave is artificially excited at the center of the bottom of the pile hole; ③ The reflected waves received by the double detectors at the bottom of the pile hole are recorded by the shallow seismometer; ④ The waveform records are analyzed and studied to determine whether there are karst caves and troughs within a certain range at the bottom of the pile hole Or bad geological conditions such as broken zone. The method of the invention does not need to carry out geological survey drilling at the bottom of the pile hole, so that the detection cost of the bearing layer is greatly reduced and the detection speed is fast.

Invention patent CN201711353299 provides a method for determining the bearing layer of cast-in-place piles by high-pressure water spray camera, comprising the following steps: (1) erecting a hoist just above the pile hole, and hoisting the camera group on the hoist through a wire rope; (2) Extend the high-pressure water pipe to and fix it on the camera group; (3) slowly put the camera group into the bottom of the pile hole through the hoist, and spray the high-pressure water into the bottom of the pile hole through the high-pressure water pipe to form a clear water section at the bottom of the pile hole, and pass The camera group observes the rock formation at the bottom of the pile hole and records the hole wall condition; (4) The camera group is taken out through the hoist. In this way, the rock formation at the bottom of the pile hole observed and recorded by the camera group is more intuitive, and it can be clearly judged whether the cast-in-place pile enters the bearing layer in its full section. The method for determining the bearing layer of a cast-in-place pile provided by the high-pressure water spray camera provided by the present invention is used to detect whether the bottom of the pile hole of the cast-in-situ pile reaches the bearing layer in its full section, and has a simple structure and more intuitive judgment.

Invention patent CN201810509888 provides a three-dimensional analysis method for the bearing layer of pile foundation, including step s1: collecting geological survey data and design and construction drawings; step s2: integrating the geological survey data and design and construction drawings into a CAD drawing; step s3: passing the The BIM software performs 3D modeling in combination with geological survey data and design and construction drawings; step s4: intercept any pile in the CAD drawing, and import the pile and several other piles on the same line into the corresponding position in the 3D model. Step s5: Cut the pile and several other piles on the same line in the three-dimensional model to obtain the cut section diagram, and calculate the actual depth of the row of piles entering the bearing layer. Step s6: Optimize the pile length. Compared with the prior art, the invention has simple operation, and can intuitively and quickly perform accurate analysis and correction on each designed pile length and bearing layer depth, thereby saving pile materials.

These methods provide some ideas for the detection of the bearing layer, but these methods still cannot accurately judge whether the screw pile has entered the bearing layer in time. Therefore, there is a need in the art for a new method for judging whether the screw pile enters the bearing layer.

SUMMARY OF THE INVENTION

Torque sensors, also known as torque sensors, torque sensors, torque sensors, and torque meters, are divided into two categories: dynamic and static. Dynamic torque sensors can also be called torque sensors, torque speed sensors, non-contact torque sensors, and rotational torque. sensors, etc. Torque sensors are the detection of torsional torque sensing on various rotating or non-rotating mechanical components. Torque sensors convert physical changes in torque into precise electrical signals.

The invention provides a method for judging whether a screw pile has entered a bearing layer. The method includes installing a torque sensor at the junction of an auger power head and a screw, monitoring the torque received during the drilling process of the screw in real time, and obtaining the relationship between the torque and the depth. According to the change characteristics of the relationship curve, it is judged whether the pile end reaches the bearing layer during the drilling process of the screw pile.

In a specific embodiment, after the relationship curve is obtained, it is judged whether the pile end reaches the bearing layer during the drilling process of the screw pile according to its change characteristics and combined with geological survey data.

In a specific embodiment, the method includes the following steps:

Step 1. Install a torque sensor at the connection between the auger power head and the screw;

Step 2, the auger is in place, starts drilling, and obtains real-time data of the change of torque T with depth h;

Step 3. Obtain the T-h curve through the electronic recording instrument;

Step 4: Divide the soil layer by section according to the change characteristics of the T-h curve to obtain the soil layer where the drill bit is located in real time;

Step 5: According to the real-time soil layer where the drill bit is located, combined with the position of the force-bearing layer in the engineering geological survey data, determine whether the force-bearing layer is reached.

The invention at least has the following beneficial effects: the invention can timely, accurately and intuitively judge whether the pile end reaches the bearing layer during the construction of the screw pile, ensure the quality of the foundation reinforcement treatment, speed up the construction progress, and at the same time ensure the bearing capacity of the screw pile, Effectively control the length of the pile and reduce the cost.

Description of drawings

FIG. 1 is a flow chart of the method for determining whether the screw pile enters the bearing layer according to the present invention.

FIG. 2 is a T-h curve diagram in a specific embodiment.

Detailed ways

In view of the current screw pile construction, the method of judging whether the pile end enters the bearing layer has the defects of slow detection speed, great influence by the experience of the drilling rig operator, and low accuracy. The invention proposes a method of installing a torque sensor at the junction of the auger power head and the screw, monitoring the torque received during the drilling process of the screw in real time, obtaining a torque-depth curve, and judging the screw according to its variation characteristics and combined with geological survey data. The method of whether the pile end reaches the bearing layer during the drilling process of the pile makes the judgment of whether the pile end of the screw pile reaches the bearing layer is more scientific, accurate, timely and intuitive.

Working principle: During the drilling process of the screw pile, the feed force and torque generated by the auger engine are transmitted to the special screw, so that the screw can impact and cut the soil, thereby achieving the effect of drilling into a hole. During drilling, under a certain feed force, the torque in the same soil layer changes with the increase of depth, and the change trend is linear as a whole; for different soil layers, due to the differences in physical and mechanical properties, the torque will inevitably change with the There are obvious changes with the change of the soil layer, and there are different linear relationships in different soil layers. Therefore, stratum feature identification can be realized by analyzing the variation trend of torque with depth and the mapping relationship of soil layers.

Through the torque sensor installed at the junction of the auger power head and the screw, the torque of the screw during the drilling process is monitored in real time, and it is displayed and recorded by the electronic measuring and recording instrument to obtain the T-h curve. In the same soil layer, when the feeding force is constant, the torque changes with the drilling depth are consistent. For different soil layers, due to the different physical and mechanical properties of the soil, this change with depth Variation characteristics can be significantly different. The T-h curve is reflected as follows: in the same soil depth range, the variation trend of torque T with depth is linear. In the sections with different soil depths, there are obvious differences in the variation trend of torque T with depth. Therefore, by reading the changing characteristics of the T-h curve, it can be divided into different soil layer sections, and it can be judged that the drill bit reaches the soil layer under the surface in real time when drilling, and combined with the approximate position of the bearing layer of the geological survey data, it can be accurately real-time. It can be judged whether the pile end has reached the bearing layer during the drilling process of the screw pile.

During the drilling process, the feeding force remains relatively stable. Under this condition, the variation trend of the torque T with the depth is examined, that is, the position of the bearing layer can be basically determined by examining the T-h curve, and the bearing force can be basically determined by combining the geological survey data of the project. The approximate position of the layer can accurately determine the depth of the bearing layer at this position. For example, in the embodiment shown in Fig. 2, the variation trend of the torque T with the depth h is given. The multiple black dots in Fig. 2 represent the real-time torque values measured at different depths. It can be seen from Fig. 2 that during drilling When the depth is 0 to 3.65 meters, the torque value does not fluctuate much up and down, and the fitted line is a straight line that slopes slightly upward to the right, and is corresponding to sandy loess. When the drilling depth is above 3.65 meters, the torque value increases rapidly, and the fitted straight line is a straight line that slopes sharply to the upper right, and the corresponding coarse round gravel soil. It can be preliminarily determined that the position is the holding layer. Combined with the geological survey data, it can be further judged and confirmed that the pile end has reached the bearing layer during the drilling process of the screw pile.

The above embodiments are only examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the embodiments of the present invention. Under the condition that the basic idea and essence of the present invention are not changed, any transformation or modification of other equivalent technical features shall fall within the protection scope of the claims of the present invention.

Claims (3)

1. A method for judging whether a screw pile enters a bearing stratum or not is characterized by comprising the steps of installing a torque sensor at the joint of a power head of a spiral drilling machine and a screw, monitoring the torque received by the screw in the drilling process in real time to obtain a relation curve of the torque and the depth, and judging whether the pile end reaches the bearing stratum or not in the drilling process of the screw pile according to the change characteristics of the relation curve.

2. The method for determining whether the screw pile enters the bearing stratum according to claim 1, wherein after the relationship curve is obtained, whether the pile tip reaches the bearing stratum during the drilling process of the screw pile is determined according to the change characteristics of the relationship curve and geological survey data.

3. A method for determining whether a screw pile enters a bearing stratum according to claim 1 or 2, comprising the steps of:

step one, a torque sensor is arranged at the connection position of a power head and a screw of a spiral drilling machine;

secondly, the spiral drilling machine is put in place, drilling is started, and real-time data of the torque T changing along with the depth h are obtained;

step three, obtaining a T-h curve through an electronic recording instrument;

dividing soil layers according to the T-h curve change characteristics and sections to obtain the soil layer where the drill bit is located in real time;

and fifthly, judging whether the drill reaches the bearing stratum or not according to the real-time soil layer of the drill and the position of the bearing stratum of the engineering geological exploration data.

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